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A series of complex parhelia displays in Rome in 1629, and again in 1630, were described by Christoph Scheiner in his book Parhelia, one of the earliest works on the subject. It had a profound effect, causing René Descartes to interrupt his metaphysical studies and led to his work of natural philosophy called The World.
On 20 February 1661 the people of Gdańsk witnessed a complex halo display, described by Georg Fehlau in a pamphlet, the Sevenfold Sun Miracle, and again the following year by Johannes Hevelius in his book, Mercurius in Sole visus Gedani.
On 18 June 1790 Johann Tobias Lowitz, in Saint Petersburg, Russia, observed a complex display of haloes and parhelia which included his Lowitz arcs.
Late modern era to current day
In 1843, winter in the British Colony of Newfoundland was referred to as the 'Winter of Three Suns' and was unusually cold with 15 days of temperatures between 3–10 degrees below zero.
"Part of the time we marched in the teeth of a biting storm of snow, and at every hour of the day the sun could be discerned sulking behind soft grey mists in company with rivals, known in the language of the plains as 'Sun-dogs', whose parahelic splendors warned the traveler of the approach of the ever-to-be-dreaded 'blizzard'."
On 14 February 2020, the people of Inner Mongolia Autonomous Region witnessed a different complex halo display called the Five-fold sun miracle, in which all five sun halos were linked to each other by rays, forming a circle among them. | Sun dog | Wikipedia | 334 | 323221 | https://en.wikipedia.org/wiki/Sun%20dog | Physical sciences | Atmospheric optics | Earth science |
Napa cabbage (Brassica rapa subsp. pekinensis, or Brassica rapa Pekinensis Group) is a type of Chinese cabbage originating near the Beijing region of China that is widely used in East Asian cuisine. Since the 20th century, it has also become a widespread crop in Europe, the Americas, and Australia. In much of the world, it is referred to as "Chinese cabbage".
Names
The word "napa" in the name napa cabbage comes from colloquial and regional Japanese, where nappa () refers to the leaves of any vegetable, especially when used as food. The Japanese name for this specific variety of cabbage is hakusai (), a Sino-Japanese reading of the Chinese name báicài (), literally "white vegetable". The Korean name for napa cabbage, baechu (), is a nativized word from the Sino-Korean reading, , of the same Chinese character sets. Today in Mandarin Chinese, napa cabbage is known as dàbáicài (), literally "big white vegetable", as opposed to the "small white vegetable" that is known in English as bok choy.
Outside of Asia, this vegetable is also referred to as Chinese cabbage or sometimes celery cabbage. It is also known as siu choy (Cantonese ), wombok in Australia and wong bok or won bok in New Zealand, all corruptions of wong ngaa baak (Cantonese ). In the United Kingdom this vegetable is known as Chinese leaf or winter cabbage, and in the Philippines as petsay (from Hokkien, ) or pechay baguio. Another name used in English is petsai or pe-tsai. In Ukraine it is called (), and in Poland - , literally "Beijing cabbage". In Sweden it is known as (salad cabbage) or sometimes (china cabbage). | Napa cabbage | Wikipedia | 390 | 14447311 | https://en.wikipedia.org/wiki/Napa%20cabbage | Biology and health sciences | Leafy vegetables | Plants |
Origin
The first records of napa cabbage cultivation date back to the 15th century in the Yangtze River region in China. From China it later spread to Korea and Japan. Beginning in the 19th century with the Chinese diaspora, it was distributed to the rest of Asia, Europe, America as well as Australia. During the 19th century napa cabbage was first introduced to America from Europe and the supply of seed materials from Europe continued until World War I. After the blockade of the European seed supply, US government research institutes and the seed industry developed new seed stocks for vegetable crops. Oregon and California were the cabbage seed production areas during that time. Today it is cultivated and eaten throughout the world.
Napa cabbage might have originated from natural hybridization between turnip (Brassica rapa subsp. rapa) and pak-choi (Brassica rapa subsp. chinensis). Artificial crosses between these two subspecies, as well as molecular data, strengthen this suggestion.
Description
The leaves, which are the harvested organ, lay side by side densely, are lime green coloured with white leaf veins and have a smooth surface. The vegetable has an oval form and weighs . The leaves are organized in basal rosettes. The flowers are yellow and have a typical Brassicaceae cross-linked arrangement, hence the name Crucifereae, which means “cross-bearing”. Because the plant is harvested in an earlier stage than flowering, normally the flowers are not visible on the field.
It develops similar to other head-forming leaf vegetables, for example cabbage lettuce. The chronological stages on the BBCH-scale are germination, leaf formation, vegetative growth (head-forming), appearance of the sprout that bears the flowers, flowering, fruit development, seed ripening and senescence.
Napa cabbage is an annual plant that reaches the generative period in the first year. It must be consumed in its vegetative period, so there is a challenge in cultivation not to reach the stadium of flowering. The stadium of flowering can be initiated by cold temperatures or the length of the day. Napa cabbage reproduces mainly by allogamy. Napa cabbage produces more leaves, bigger leaves and a higher biomass under long day conditions than under short day conditions.
Uses
Culinary | Napa cabbage | Wikipedia | 460 | 14447311 | https://en.wikipedia.org/wiki/Napa%20cabbage | Biology and health sciences | Leafy vegetables | Plants |
Napa cabbage is a cool season annual vegetable which grows best when the days are short and mild. The plant grows to an oblong shaped head consisting of tightly arranged crinkly, thick, light-green leaves with prominent white veins. Innermost layer leaves feature light yellow color.
Napa cabbage belongs to the family Brassicaceae, commonly called the mustard or cabbage family. As a cruciferous plant it is closely related to species of Brassica like broccoli, bok choy and cauliflower.
Napa cabbage is widely used in China, Japan, and Korea. Napa cabbage is used as a sign of prosperity in China, and often appears as a symbol in glass and porcelain figures. The Jadeite Cabbage sculpture of Taiwan's National Palace Museum is a carving of a napa cabbage variety. It is also found in North American and Australian cities after Asian immigrants settled in the regions.
Fermented Napa cabbage (suan cai/sauerkraut) is a traditional food in Northeast China.
In Korean cuisine, napa cabbage is the main ingredient of baechu-kimchi, the most common type of kimchi, but is also eaten raw as a wrap for pork or oysters, dipped in gochujang. The outer, tougher leaves are used in soups. It can be used in stir-fry with other ingredients, such as tofu, mushroom and zucchini. It is also eaten with hot pot meals. Napa cabbage is particularly popular in South Korea's northern Gangwon Province. In European, American and Australian kitchens, it is more common to eat it cooked or raw as salad.
The vegetable is rich in vitamin C (26 mg/100g) and has a fair amount of calcium (40 mg/100g). It tastes mildly aromatic.
Cultivation
Napa cabbage can be cultivated in many different areas of the world, the main area of diversification represents Asia.
Soil requirements
Napa cabbage requires deeply loosened medium heavy soil. There must not be any compaction due to plowing. The crop achieves particularly high yields on sandy loam. Extremely sandy or claylike soils are not suitable.
The crop prefers a pH range from 6.0 to 6.2, a high organic matter content and good moisture holding capacity of the soil. Lower pH or droughty soil can lead to calcium or magnesium deficiency and internal quality defects. | Napa cabbage | Wikipedia | 487 | 14447311 | https://en.wikipedia.org/wiki/Napa%20cabbage | Biology and health sciences | Leafy vegetables | Plants |
Climate requirements
Napa cabbage needs much water during the whole growth period. Often an irrigation system is needed, especially for August and September. The required amount of water depends on the stage of crop growth, weather conditions, and soil type. The most critical stage after establishment is when the head is forming. Inadequate water at this time will result in reduced uptake of calcium. This condition causes dead leaf tips within the head which makes it unmarketable. During head formation, of water per week is needed to maintain sustained growth rates.
Temperature requirements are low. Temperatures below are tolerated for short time periods; persistent frosts below are not endured. Too low temperature can induce premature bolting. The plants perform best under temperatures between , but depending on the cultivar.
Seedbed requirements & sowing
Napa cabbage has very small seeds with a thousand kernel weight of about 2.5 to 2.8 g. For professional cultivation it is recommended to use disinfected seeds to prevent onset diseases. With the single-grain sowing technique, about 400 to 500 g of seeds per hectare is required; with the normal sowing technique, about 1 kg per hectare. If the normal sowing technique is used, the seedlings must be thinned out after two to four weeks. The seeds should be deposited deep, with a row width of and distance between the seeds.
The seedlings can be grown in the greenhouse and then transplanted into the field after two to three weeks. Earlier harvest can be achieved with this method. Seventy thousand to 80,000 seedlings per hectare are required. The transplanting method is normally used for the spring crop and the seeding technique for the fall crop.
Fertilization, field management
The nutrient removal of napa cabbage is high:
150–200 kg N per hectare
80–120 kg P2O5 per hectare
180–250 kg K2O per hectare
110–150 kg Ca per hectare
20–40 kg Mg per hectare
Fertilizer recommendations are in the range of the nutrient removal. Organic fertilizer must be applied before sowing due to the short cultivation time of napa cabbage and the slow availability of organic fertilizers. Synthetic N fertilizer should be applied in three equal doses. The last application must happen before two thirds of the cultivation time is over to avoid quality losses during storage.
Weeds should be controlled mechanically or chemically.
Harvest, storage and yield | Napa cabbage | Wikipedia | 487 | 14447311 | https://en.wikipedia.org/wiki/Napa%20cabbage | Biology and health sciences | Leafy vegetables | Plants |
Napa cabbage can be harvested 8–12 weeks after sowing. The harvest work is mostly done by hand. The plant is cut above the ground. It is usual to harvest several times per field to achieve consistent cabbage quality. Cabbages will keep in good condition for three to four months in cool stores at and 85 to 90 percent relative humidity. Napa cabbage achieves a yield of 4 to 5 kg/m2.
Breeding
Brassica rapa species are diploid and have 10 chromosomes. A challenge for breeding of napa cabbage is the variable self-incompatibility. The self-incompatibility activity was reported to change by temperature and humidity. In vitro pollination with 98% relative humidity proved to be the most reliable as compared to greenhouse pollination.
A lot of work has already been done on breeding of napa cabbage. In the 21st century, 880 varieties of Napa cabbage were registered by the Korea Seed and Variety Service.
Breeding of napa cabbage was started by the Korean government research station of horticultural demonstration in 1906 to overcome starvation. As napa cabbage and radish are the main vegetables for kimchi, research focused on increasing yield. The most important person for this process was Dr. Woo Jang-choon who bred hybrid cultivars with self-incompatibility and contributed to commercial breeding by developing valuable materials and educating students. The main purpose of the hybrid cultivar was high yield and year-round production of napa cabbage after 1960.
To enable year round production of napa cabbage, it has to be modified to tolerate high and low temperatures. Normally, sowing in the late summer and harvesting in late autumn can produce high quality vegetables. As an example, a summer cultivar called “Nae-Seo-beak-ro” was developed 1973 by a commercial seed company. It tolerates high temperatures, could endure high humidity in the monsoon, and showed resistance to viral disease, soft rot and downy mildew. The low temperature in early spring reduces the quality of the vegetable and it cannot be used for kimchi. In the 1970s the developing of winter cultivars started. The majority of new cultivars could not endure the cold winter conditions and disappeared. The cultivar “Dong-Pung” (meaning “east wind”) was developed in 1992 and showed a high resistance to cold temperature. It is mostly used in Korea, where fresh napa cabbage is nowadays cultivated year round. | Napa cabbage | Wikipedia | 495 | 14447311 | https://en.wikipedia.org/wiki/Napa%20cabbage | Biology and health sciences | Leafy vegetables | Plants |
In the 1970s, one seed company developed the rose-shape heading variety while other seed companies focused on the semi-folded heading type. As a result of continuous breeding in the commercial seed companies and the government research stations, farmers could now select what they wanted from among various high quality hybrids of Chinese cabbage. The fall season cultivar 'Yuki', with white ribs and tight leaf folding, gained the RHS's Award of Garden Merit (AGM) in 2003.
In 1988, the first cultivar with yellow inner leaf was introduced. This trait has prevailed until today.
A very important breeding aim is to get varieties with resistance to pests and diseases. There exist varieties with resistance to turnip mosaic virus but as mentioned above, there exist numerous other diseases. There have been attempts to breed varieties with clubroot resistance or powdery mildew resistance but the varieties failed due to bad leaf texture traits or broken resistances.
Pests and diseases | Napa cabbage | Wikipedia | 191 | 14447311 | https://en.wikipedia.org/wiki/Napa%20cabbage | Biology and health sciences | Leafy vegetables | Plants |
Fungal diseases
Alternaria diseases are caused by the organisms Alternaria brassicae, Alternaria brassicicola and Alternaria japonica. Their English names are black spot (not to be confused with midrib 'pepper spots' which are physiological in origin and often result from improper storage), pod spot, gray leaf spot, dark leaf spot or Alternaria blight. The symptoms can be seen on all aboveground plant parts as dark spots. The infected plants are shrivelled and smaller than normal. Alternaria diseases infect almost all brassica plants, the most important hosts are oilseed brassicas.
The fungus is a facultative parasite, what means that it can survive on living hosts as well as on dead plant tissue. Infected plant debris is in most circumstances the primary source of inoculum. The spores can be dispersed by wind to host plants in the field or to neighbouring brassica crops. This is why cross infections often occur in areas where different brassica crops are cultivated in close proximity. The disease spreads especially fast when the weather is wet and the plants have reached maturity.
Alternaria brassicae is well adapted to temperate regions while Alternaria brassicicola occurs primarily in warmer parts of the world. Temperature requirement for Alternaria japonica is intermediate.
There exist some wild accessions of Brassica rapa subsp. pekinensis with resistance to Alternaria brassicae but not on commercial cultivars. These resistances should be included to breeding programmes. Alternaria epidemics are best avoided by management practices like at least 3 years non-host crops between brassica crops, incorporation of plant debris into the soil to accelerate decomposition and usage of disease-free seeds.
Anhracnose is a brassica disease caused by Colletotrichum higginsianum that is especially damaging on napa cabbage, pak choi, turnip, rutabaga and tender green mustard. The symptoms are dry pale gray to straw spots or lesions on the leaves. The recommended management practices are the same as for Alternaria diseases.
Black root is a disease that infects mainly radish, but it also occurs on many other brassica vegetables inclusively napa cabbage. It caused by the fungus Aphanomyces raphani. The pathogen can persist for long times in the soil, therefore crop rotations are an essential management tool. | Napa cabbage | Wikipedia | 492 | 14447311 | https://en.wikipedia.org/wiki/Napa%20cabbage | Biology and health sciences | Leafy vegetables | Plants |
White leaf spot is found primarily in temperate climate regions and is important on vegetable brassicas and oilseed rape. The causal organism is Mycosphaerella capsellae. The symptoms are white spots on leaves, stems and pods and can thus easily be confused with those of downy mildew. The disease spreads especially fast with rain or moisture and temperature is between .
Yellows, also called Fusarium wilt, is another Brassica disease that infects oilseed rape, cabbage, mustards, Napa cabbage and other vegetable brassicas. It is only a problem in regions with warm growing seasons where soil temperatures are in the range of 18 to 32 °C. The causal organism is Fusarium oxysporum f. sp. conlutinans. Napa cabbage is relatively tolerant to the disease; mostly the only external symptoms are yellowing of lower, older leaves. The disease is soil borne and can survive for many years in the absence of a host. Most cruciferous weeds can serve as alternate hosts.
Damping-Off is a disease in temperate areas caused by soil inhabiting oomycetes like Phytophthora cactorum and Pythium spp. The disease concerns seedlings, which often collapse and die.
Other diseases that infect napa cabbage:
black leg or phoma stem cancer: Leptosphaeria maculans
clubroot: Plasmodiophora brassicae
Downy mildew: Hyaloperonospora brassicae
Powdery mildew: Erysiphe cruciferarum
Rhizoctonia solani
Sclerotinia sclerotiorum
Bacterial diseases
Bacterial soft rot is considered one of the most important diseases of vegetable brassicas. The disease is particularly damaging in warm humid climate. The causal organisms are Erwinia carotovora var. carotovora and Pseudomonas marginalis pv. marginalis. The rot symptoms can occur in the field, on produce transit or in storage.
Bacteria survive mainly on plant residues in the soil. They are spread by insects and by cultural practices, such as irrigation water and farm machinery. The disease is tolerant to low temperatures; it can spread in storages close to 0 °C, by direct contact and by dripping onto the plants below.
Bacterial soft rot is more severe on crops which have been fertilized too heavily with nitrogen, had late nitrogen applications, or are allowed to become over-mature before harvesting. | Napa cabbage | Wikipedia | 505 | 14447311 | https://en.wikipedia.org/wiki/Napa%20cabbage | Biology and health sciences | Leafy vegetables | Plants |
Black rot, the most important disease of vegetable brassicas, is caused by Xanthomonas campestris pv. campestris.
Virus diseases
source:
Cucumber mosaic virus
Radish mosaic virus
Ribgrass mosaic virus
Turnip crinkle virus
Cardamine chlorotic fleck virus
Turnip mosaic virus
Turnip yellow mosaic virus
Insect pests
source:
large white butterfly (Pieris brassicae)
cabbage root fly (Delia radicum)
cabbage seed weevil (Ceutorhynchus assimilis)
cabbage looper
cabbage beetle (Colaphellus bowringi)
diamondback moth
small white butterfly (Pieris rapae)
aphids
cucumber beetles
stink bugs
Vegetable weevils
Mole crickets
cutworms
Other pests and diseases
Aster yellows is a disease caused by a phytoplasm.
Nematodes are disease agents that are often overlooked but they can cause considerable yield losses. The adult nematodes have limited active movement but their eggs contained within cysts (dead females) are readily spread with soil, water, equipment or seedlings.
Parasitic nematode species that cause damage on napa cabbage:
Heterodera schachtii
Meloidogyne hapla
Nacobbus batatiformis
Rotylenchulus reniformis | Napa cabbage | Wikipedia | 270 | 14447311 | https://en.wikipedia.org/wiki/Napa%20cabbage | Biology and health sciences | Leafy vegetables | Plants |
Palaeotheriidae is an extinct family of herbivorous perissodactyl mammals that inhabited Europe, with less abundant remains also known from Asia, from the mid-Eocene to the early Oligocene. They are classified in Equoidea, along with the living family Equidae (which includes zebras, horses and asses).
Morphology
Palaeotheres ranged widely in size, from small species like Palaeotherium lautricense, which is estimated to have only weighed to large species like Palaeotherium magnum, which are comparable in size to living equines, with body masses over . Their teeth are brachydont (low crowned). According to Danilo et al. 2013., paleotheriids are distinguished from other equoids by one unambiguous synapomorphy "the nasal notch opening distally to the canine, above the postcanine diastema" and two unambiguous character state changes "an average metaconule on [the fourth premolar]" and "an oblique metastyle on [the first and second molars]".
Taxonomy
Palaeotheriidae is generally divided into the subfamilies Palaeotheriinae and ‘Pachynolophinae'. The two groups are distinguished by the morphology of their upper molars, with mesostyles being at least moderately developed in those Palaeotheriinae, but generally weakly developed or absent in those of 'Pachylophinae'. 'Pachylophinae' is controversial with regards to its definition and phylogenetic placement. 'Pachylophinae', along with the genus Pachynolophus has been argued to be a paraphyletic group that is ancestral to Palaeotheriinae.
Ecology
Early members of the family are suggested to have been frugivores, with later, larger members suggested to be browsers.
Extinction | Palaeotheriidae | Wikipedia | 399 | 10802532 | https://en.wikipedia.org/wiki/Palaeotheriidae | Biology and health sciences | Perissodactyla | Animals |
Evidence suggests that palaeotheriids went extinct in Eurasia during the Early Oligocene, approximately 33 Ma, as part of a faunal turnover event known as the Grande Coupure. The Eocene-Oligocene transition marked a significant global cooling event caused by the onset of Antarctic glaciation. This resulted in drier and more open habitats dominating the early Oligocene, and the loss of the dense forests that characterised the Eocene epoch. This environmental change, coupled with the arrival of new and better-adapted mammalian groups from Asia, triggered a decline in endemic European mammal groups such as Palaeotheriidae and Anoplotheriidae. In the Hampshire Basin of southern England the last record of Palaeotheriidae is from the Lower Hamstead Mbr. of the Bouldnor Formation, dating to approximately 33.6 Ma.
Fossil distribution
Creechbarrow Hill Site, Dorset, England
Geiseltal, Mittelkohle, Zone III, Saxony-Anhalt, Germany
Egerkingen, Alpha & Beta fissures, Baselland, Switzerland
La Debruge, Provence-Alpes-Côte d'Azur Region, France
The Caucasus Mountains in Georgia | Palaeotheriidae | Wikipedia | 244 | 10802532 | https://en.wikipedia.org/wiki/Palaeotheriidae | Biology and health sciences | Perissodactyla | Animals |
Protoceratidae is an extinct family of herbivorous North American artiodactyls (even-toed ungulates) that lived during the Eocene through Pliocene. While early members of the group were hornless, in later members males developed elaborate cranial ornamentation. They are variously allied with Ruminantia or Tylopoda.
Classification
Protoceratidae was erected by Othniel Charles Marsh in 1891, with the type genus Protoceras and assigned to the Artiodactyla. It was later assigned to Pecora, and more recently to Ruminantia or Tylopoda. However, recently a relationship to chevrotains in the infraorder Tragulina has been proposed.
Morphology
When alive, protoceratids would have resembled deer, though they were not directly related. Protoceratids ranged from 1 to 2 m in length, from about the size of a roe deer to an elk. Unlike many modern ungulates, they lacked cannon bones in their legs. Their dentition was similar to that of modern deer and cattle, suggesting they fed on tough grasses and similar foods, with a complex stomach similar to that of camels. At least some forms are believed to have lived in herds.
The most dramatic feature of the protoceratids, however, were the horns of the males. In addition to having horns in the more usual place, protoceratids had additional, rostral horns above their noses. These horns were either paired, as in Syndyoceras, or fused at the base, and branching into two near the tip, as in Synthetoceras. In life, the horns were probably covered with skin, much like the ossicones of a giraffe. The females were either hornless, or had far smaller horns than the males. Horns were therefore probably used in sexual display or competition for mates. In later forms, the horns were large enough to have been used in sparring between males, much as with the antlers of some modern deer.
Genera by epoch
Eocene
Heteromeryx
Leptoreodon
Leptotragulus
Poabromylus
Pseudoprotoceras
Toromeryx
Trigenicus
Oligocene
Protoceras
Miocene
Paratoceras
Lambdoceras
Prosynthetoceras
Synthetoceras
Syndyoceras
Pliocene
Kyptoceras | Protoceratidae | Wikipedia | 492 | 10802893 | https://en.wikipedia.org/wiki/Protoceratidae | Biology and health sciences | Other artiodactyla | Animals |
An arroyo ( (from Spanish arroyo (, "brook"))) or wash is a dry watercourse that temporarily or seasonally fills and flows after sufficient rain. Flash floods are common in arroyos following thunderstorms. It's akin to the Catalan rambla, which stems from the Arabic rámla, "dry river".
Similar landforms are referred to as wadi (in North Africa and Western Asia), chapp in the Gobi, laagate in the Kalahari, donga in South Africa, nullah in India, fiumare in Italy, and dry valley in England.
The desert dry wash biome is restricted to the arroyos of the southwestern United States. Arroyos provide a water source to desert animals.
Types and processes
Arroyos can be natural fluvial landforms or constructed flood control channels. The term usually applies to a sloped or mountainous terrain in xeric and desert climates. In addition: in many rural communities arroyos are also the principal transportation routes; and in many urban communities arroyos are also parks and recreational locations, often with linear multi-use bicycle, pedestrian, and equestrian trails. Flash flooding can cause the deep arroyos or deposition of sediment on flooded lands. This can lower the groundwater level of the surrounding area, making it unsuitable for agriculture. However a shallow water table lowered in desert arroyo valleys can reduce saline seeping and alkali deposits in the topsoil, making it suitable for irrigated farming. | Arroyo (watercourse) | Wikipedia | 300 | 1519419 | https://en.wikipedia.org/wiki/Arroyo%20%28watercourse%29 | Physical sciences | Hydrology | Earth science |
Natural
The Doña Ana County Flood Commission in the U.S. state of New Mexico defines an arroyo as "a watercourse that conducts an intermittent or ephemeral flow, providing primary drainage for an area of land of or larger; or a watercourse which would be expected to flow in excess of one hundred cubic feet per second as the result of a 100 year storm event." Research has been conducted in the hydrological modeling relative to arroyos.
Natural arroyos are made through the process known as arroyo-cutting. This occurs in arid regions, such as New Mexico, where heavy rains can lead to enlargement of rivers cutting into surrounding rock creating ravines which are dry under normal weather conditions.
It is argued, however, whether these excessively stormy periods are the sole cause of arroyo-cutting as other factors such as long-term climate changes must also be taken into account. Further, overgrazing by livestock throughout the 20th century and today has removed vast amounts of surface vegetation which decreases ground infiltration of precipitation and increased runoff, increasing speed and energy of high flow rain events. Coupled with groundwater pumping this increases downcutting in arroyos as well. Arroyo cutting which occurred in the 1900s in the southwestern United States caused serious farming issues such as a lowered water table and the destruction of agriculture lands.
Constructed
In agricultural areas in climates needing irrigation, farmers traditionally relied on small constructed arroyos, acequias, zanjas or aqueduct channels and ditches for the distribution of water.
An example of larger constructed arroyos is in Albuquerque, New Mexico. There are several miles of open-air concrete lined drainage channels that drain an area into the main North Diversion Channel, a tributary of the Rio Grande joining upstream of Albuquerque. After the San Juan Project Water Treatment Plant here, the Rio Grande's flow exceeding that needed for the river's silvery minnow habitat is available for municipal water supply diversion. Signs are posted at the constructed arroyos warning to keep out due to danger of flash flooding.
The Arroyo Seco and Los Angeles River are more famous examples in Southern California of former natural arroyo seasonal watercourses that became constructed open drainage system arroyos. | Arroyo (watercourse) | Wikipedia | 439 | 1519419 | https://en.wikipedia.org/wiki/Arroyo%20%28watercourse%29 | Physical sciences | Hydrology | Earth science |
The common seadragon or weedy seadragon (Phyllopteryx taeniolatus) is a marine fish of the order Syngnathiformes, which also includes the similar pipefishes, seahorses, and trumpetfishes among other species. Adult common seadragons are a reddish colour, with yellow and purple striped markings; they have small, leaf-like appendages that resemble kelp or seaweed fronds, providing camouflage, as well as a number of short spines for protection. As with seahorses and the other syngnathids, the seadragon has a similarly tubular snout and a fused, toothless jaw into which it captures small invertebrate prey at lightning speed. Males have narrower bodies and are darker than females. Seadragons have a long dorsal fin along the back and small pectoral fins on either side of the neck, which provide balance. Weedy seadragons can reach in length.
The seadragon is the marine emblem of the Australian state of Victoria.
Range and habitat
The common seadragon is endemic to Australian and insular coastal waters of the eastern Indian Ocean northern Southern Ocean and the southwestern Pacific Ocean. It can generally be found along the entire southern coastline of the Australian continent, including Tasmania and other offshore islands. It can be observed regularly from around Port Stephens, New South Wales to Geraldton, Western Australia, as well as off the coast of South Australia and the Great Australian Bight.
The common seadragon inhabits coastal waters down around to deep. It is associated with rocky reefs, seaweed beds, seagrass meadows and structures colonised by seaweed.
Biology
The seadragons are slow-moving and, like most of their relatives, rely on excellent camouflage—the mimicry of seaweed, in this case—as a defense against predators. They lack the prehensile tail that many seahorses and pipefishes have evolved as anchors, to clasp and steady themselves; seadragons, instead, drift in the water among kelp and seaweed masses, which they blend-into with their leafy-looking appendages. | Common seadragon | Wikipedia | 445 | 1520435 | https://en.wikipedia.org/wiki/Common%20seadragon | Biology and health sciences | Acanthomorpha | Animals |
Individuals are observed either on their own or in pairs, feeding on tiny crustaceans and other zooplankton by sucking prey into their toothless mouths. As with most other syngnathids, seadragon males are the sex that cares for the developing eggs. Females lay around 120 eggs onto the brood patch located on the underside of the male's tail. The eggs are fertilised and carried by the male for around a month before the hatchlings emerge. The young are independent at birth, beginning to eat shortly after. Common seadragons take about 28 months to reach sexual maturity, and may live for up to six years.
Mating in captivity is relatively rare since researchers have yet to understand what biological or environmental factors trigger them to reproduce. The survival rate for young common seadragons is low in the wild, but it is about 60% in captivity.
The Aquarium of the Pacific (in Long Beach, California) and the Tennessee Aquarium (in Chattanooga, Tennessee), in the US, and Melbourne Aquarium in Melbourne, Australia are among the few facilities in the world to have successfully bred common seadragons in captivity, though others occasionally report egg-laying. In March 2012, Georgia Aquarium (in Atlanta) announced a successful breeding event of common seadragons. In July of the same year, Monterey Bay Aquarium, on California's central coast, successfully bred and hatched-out common seadragons, on-exhibit. Most recently, Birch Aquarium (in La Jolla, San Diego, California) successfully bred and hatched common seadragon fry in early 2023.
Aquarium keepers must make adjustments to the water, food, tank setup, and captivity procedures, as many studies have shown that sea dragons are prone to diseases and infections such as scuticociliatosis, myxozoanosis, fungal infections, intestinal coccidiosis, neoplasia, and swim bladder issues, which can result from parasites growing in their bodies due to their captive environment.
Threats
The common seadragon is classified as Least Concern (LC) on the IUCN Red List. While the common seadragon is a desired species in the international aquarium trade, the volume of wild-caught individuals is small and therefore not currently a major threat. Instead, habitat loss and degradation due to human activities and pollution threaten common seadragons most. | Common seadragon | Wikipedia | 485 | 1520435 | https://en.wikipedia.org/wiki/Common%20seadragon | Biology and health sciences | Acanthomorpha | Animals |
The loss of suitable seagrass beds and loss of canopy seaweed from inshore rock reefs, coupled with natural history traits that make them poor dispersers, put the future of seadragon populations at risk. This species is not at present a victim of bycatch or a target of trade in traditional Chinese medicine, two activities which are currently a threat to many related seahorse and pipefish populations.
More recent research suggests that the weedy seadragon may be far more endangered than initially assumed as a result of climate change-induced marine heatwaves on the Great Southern Reef. Edgar et al (2023) documented a population decline of 59% between 2011 and 2021, a period of frequent and extensive marine heatwaves. This would be enough to classify it as Endangered on the IUCN Red List.
Conservation
It is illegal to take or export these species in most of the states within which they occur. A database of seadragon sightings, known as 'Dragon Search' has been established with support from the Marine Life Society of South Australia Inc., ('Dragon Search' arose as the logical progression of a similar project initiated by the MLSSA, which was the first community group or indeed organisation of any type to adopt the common seadragon's close relative, the leafy seadragon, as part of its logo), the Marine and Coastal Community Network (MCCN), the Threatened Species Network (TSN) and the Australian Marine Conservation Society (AMCS), which encourages divers to report sightings. Monitoring of populations may provide indications of local water quality and seadragons could also become an important 'flagship' species for the often-overlooked richness of the unique flora and fauna of Australia's south coast.
Captive breeding programs are in place for the weedy seadragon, headed up by Sea Life Melbourne Aquarium. The dragon has been difficult to breed in captivity, though in 2015, research observing the creatures in the wild and trying to replicate the conditions in captivity had researchers making changes to the light, water temperature and water flow proving to be key.
In December 2015, the Melbourne aquarium hatched eggs and the aquarium's weedy seadragon population significantly increased. The aquarium reported in March 2016 that 45 fry were still going strong, a 95% survival rate. | Common seadragon | Wikipedia | 467 | 1520435 | https://en.wikipedia.org/wiki/Common%20seadragon | Biology and health sciences | Acanthomorpha | Animals |
Related species
The common seadragon is in the subfamily Syngnathinae, which contains all pipefish. It is most closely related to the other member of its genus, the ruby seadragon (Phyllopteryx dewysea), and also the leafy seadragon (Phycodurus eques). Haliichthys taeniophorus, sometimes referred to as the "ribboned seadragon" is not closely related (it does not form a true monophyletic clade with weedy and leafy seadragons).
The common seadragon was previously the only member of its genus until the description of the ruby seadragon in 2015.
Ongoing research
In the November 2006 issue of National Geographic magazine, marine biologist Greg Rouse is reported as investigating the DNA variation of the two seadragon species across their ranges. | Common seadragon | Wikipedia | 179 | 1520435 | https://en.wikipedia.org/wiki/Common%20seadragon | Biology and health sciences | Acanthomorpha | Animals |
The Caribbean plate is a mostly oceanic tectonic plate underlying Central America and the Caribbean Sea off the northern coast of South America.
Roughly in area, the Caribbean plate borders the North American plate, the South American plate, the Nazca plate and the Cocos plate. These borders are regions of intense seismic activity, including frequent earthquakes, occasional tsunamis, and volcanic eruptions.
Boundary types
The northern boundary with the North American plate is a transform or strike-slip boundary that runs from the border area of Belize, Guatemala (Motagua Fault), and Honduras in Central America, eastward through the Cayman trough along the Swan Islands Transform Fault before joining the southern boundary of the Gonâve microplate. East of the Mid-Cayman Rise this continues as the Walton fault zone and the Enriquillo–Plantain Garden fault zone into eastern Hispaniola. From there it continues into Puerto Rico, and the Virgin Islands. Part of the Puerto Rico Trench, the deepest part of the Atlantic Ocean (roughly ), lies along this border. The Puerto Rico Trench is at a complex transition from the subduction boundary to the south and the transform boundary to the west.
The eastern boundary is a subduction zone, the Lesser Antilles subduction zone, where oceanic crust of the South American plate is being subducted under the Caribbean plate. Subduction forms the volcanic islands of the Lesser Antilles Volcanic Arc from the Virgin Islands in the north to the islands off the coast of Venezuela in the south. This boundary contains seventeen active volcanoes, most notably Soufriere Hills on Montserrat; Mount Pelée on Martinique; La Grande Soufrière on Guadeloupe; Soufrière Saint Vincent on Saint Vincent; and the submarine volcano Kick 'em Jenny which lies about 10 km north of Grenada. Large historical earthquakes in 1839 and 1843 in this region are possibly megathrust earthquakes. | Caribbean plate | Wikipedia | 380 | 1521467 | https://en.wikipedia.org/wiki/Caribbean%20plate | Physical sciences | Tectonic plates | Earth science |
Along the geologically complex southern boundary, the Caribbean plate interacts with the South American plate forming Barbados, Trinidad and Tobago (all on the Caribbean plate), and islands off the coast of Venezuela (including the Leeward Antilles) and Colombia. This boundary is in part the result of transform faulting, along with thrust faulting and some subduction. The rich Venezuelan petroleum fields possibly result from this complex plate interaction. The Caribbean plate is moving eastward about per year in relation to the South American plate. In Venezuela, much of the movement between the Caribbean plate and the South American plate occurs along the faults of Boconó, El Pilar, and San Sebastián.
The western portion of the plate is occupied by Central America. The Cocos plate in the Pacific Ocean is subducted beneath the Caribbean plate, just off the western coast of Central America. This subduction forms the volcanoes of Guatemala, El Salvador, Nicaragua, and Costa Rica, also known as the Central America Volcanic Arc.
Origin
The usual theory of the origin of the Caribbean plate was confronted by a contrasting theory in 2002.
The mainstream theory holds that it is the Caribbean large igneous province (CLIP) which formed in the Pacific Ocean tens of millions of years ago, perhaps originating at the Galápagos hotspot. As the Atlantic Ocean widened, North America and South America were pushed westward, separated for a time by oceanic crust. The Pacific Ocean floor subducted under this oceanic crust between the continents. The CLIP drifted into the same area, but as it was less dense and thicker than the surrounding oceanic crust, it did not subduct, but rather overrode the ocean floor, continuing to move eastward relative to North America and South America. With the formation of the Isthmus of Panama 3 million years ago, it ultimately lost its connection to the Pacific.
The more recent theory asserts that the Caribbean plate came into being from an Atlantic hotspot which no longer exists. This theory points to evidence of the absolute motion of the Caribbean plate which indicates that it moves westward, not east, and that its apparent eastward motion is only relative to the motions of the North American plate and the South American plate. | Caribbean plate | Wikipedia | 438 | 1521467 | https://en.wikipedia.org/wiki/Caribbean%20plate | Physical sciences | Tectonic plates | Earth science |
First American land bridge
The Caribbean plate began its eastward migration (Ma) during the Late Cretaceous. This migration eventually resulted in a volcanic arc stretching from northwestern South America to the Yucatán Peninsula, today represented by the Aves Islands and the Lesser and Greater Antilles. This arc was the subject of constant tectonism and sea-level fluctuation, but lasted until the mid-Eocene and intermittently formed a land bridge along the eastern and northern boundaries of the Caribbean plate. What would eventually become present-day Central America, part of the western plate boundary, was still isolated in the Pacific.
, during the Late Paleocene, a local sea-level low-stand assisted by the continental uplift of the western margin of South America, resulted in a fully operative land bridge over which several groups of mammals apparently took part in an interchange. For example, specimens have been assigned to xenarthra, didelphidae, and phorusrhacidae from Eocene North America and Europe (although these have been criticized), and Peradectes from Paleocene South America.
Great American Interchange
The Great American Interchange in which land and freshwater fauna migrated between North America and South America via the uplifted western margin of the Caribbean plate (Central America) was a later event, which peaked dramatically around 2.6 million years (Ma) ago during the Piacenzian age. | Caribbean plate | Wikipedia | 279 | 1521467 | https://en.wikipedia.org/wiki/Caribbean%20plate | Physical sciences | Tectonic plates | Earth science |
Epsilon Canis Majoris is a binary star system and the second-brightest star in the constellation of Canis Major. Its name is a Bayer designation that is Latinised from ε Canis Majoris, and abbreviated Epsilon CMa or ε CMa. This is the 22nd-brightest star in the night sky with an apparent magnitude of 1.50. About 4.7 million years ago, it was the brightest star in the night sky, with an apparent magnitude of −3.99. Based upon parallax measurements obtained during the Hipparcos mission, it is about 405 light-years distant.
The two components are designated ε Canis Majoris A, officially named Adhara – the traditional name of the system, and B.
Nomenclature
ε Canis Majoris (Latinised to Epsilon Canis Majoris) is the binary system's Bayer designation. The designations of the two components as ε Canis Majoris A and B derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).
ε Canis Majoris bore the traditional name Adhara (sometimes spelled Adara, Adard, Udara or Udra), derived from the Arabic word عذارى 'aðāra', "virgins". In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire star systems. It approved the name Adhara for the star ε Canis Majoris A on 21 August 2016 and it is now so included in the List of IAU-approved Star Names.
In the 17th-century catalogue of stars in the Calendarium of Al Achsasi al Mouakket, this star was designated Aoul al Adzari (أول العذاري awwal al-adhara), which was translated into Latin as Prima Virginum, meaning First of the Virgins. Along with δ Canis Majoris (Wezen), η Canis Majoris (Aludra) and ο2 Canis Majoris (Thanih al Adzari), these stars were Al ʽAdhārā (العذاري), 'the Virgins'. | Epsilon Canis Majoris | Wikipedia | 480 | 1522271 | https://en.wikipedia.org/wiki/Epsilon%20Canis%20Majoris | Physical sciences | Notable stars | Astronomy |
In Chinese, (), meaning Bow and Arrow, refers to an asterism consisting of ε Canis Majoris, δ Canis Majoris, η Canis Majoris, κ Canis Majoris, ο Puppis, π Puppis, χ Puppis, c Puppis and k Puppis. Consequently, ε Canis Majoris itself is known as (, ).
Physical properties
ε Canis Majoris is a binary star. The primary, ε Canis Majoris A, has an apparent magnitude of +1.5 and belongs to the spectral classification B2. Its color is blue or blueish-white, due to the surface temperature of . It emits a total radiation equal to 38,700 times that of the Sun. This star is the brightest source of extreme ultraviolet in the night sky. It is the strongest source of photons capable of ionizing hydrogen atoms in interstellar gas near the Sun, and is very important in determining the ionization state of the Local Interstellar Cloud. Its rotation period is estimated to be about 5 days.
The exact evolutionary status of is uncertain. Spectroscopically it has been given the class B2 II, with the luminosity class of II indicating that is a bright giant, more luminous than a typical giant (luminosity class III). However, it appear less luminous than the expected for this luminosity class, and is more likely of class B2 III-II. Two studies suggest is still in the late main sequence (TAMS), rather than being a giant. One of these even suggested it could be the final product of a stellar merger.
The +7.5-magnitude (the absolute magnitude amounts to +1.9) companion star, ε Canis Majoris B, is away with a position angle of 161° of the main star. Despite the relatively large angular distance the components can only be resolved in large telescopes, since the primary is approximately 250 times brighter than its companion.
A few million years ago, ε Canis Majoris was much closer to the Sun than it is at present, causing it to be a much brighter star in the night sky. About 4.4 million years ago, Adhara was light-years from the Sun, and was the brightest star in the sky with a magnitude of . The values adoptedNo other star has attained this brightness since, nor will any other star attain this brightness for at least five million years. | Epsilon Canis Majoris | Wikipedia | 496 | 1522271 | https://en.wikipedia.org/wiki/Epsilon%20Canis%20Majoris | Physical sciences | Notable stars | Astronomy |
In culture
USS Adhara (AK-71) was a U.S. Navy Crater-class cargo ship named after the star.
ε Canis Majoris appears on the national flag of Brazil, symbolising the state of Tocantins. | Epsilon Canis Majoris | Wikipedia | 50 | 1522271 | https://en.wikipedia.org/wiki/Epsilon%20Canis%20Majoris | Physical sciences | Notable stars | Astronomy |
A soil horizon is a layer parallel to the soil surface whose physical, chemical and biological characteristics differ from the layers above and beneath. Horizons are defined in many cases by obvious physical features, mainly colour and texture. These may be described both in absolute terms (particle size distribution for texture, for instance) and in terms relative to the surrounding material, i.e. 'coarser' or 'sandier' than the horizons above and below.
The identified horizons are indicated with symbols, which are mostly used in a hierarchical way. Master horizons (main horizons) are indicated by capital letters. Suffixes, in form of lowercase letters and figures, further differentiate the master horizons. There are many different systems of horizon symbols in the world. No one system is more correct—as artificial constructs, their utility lies in their ability to accurately describe local conditions in a consistent manner. Due to the different definitions of the horizon symbols, the systems cannot be mixed.
In most soil classification systems, horizons are used to define soil types. The German system uses entire horizon sequences for definition. Other systems pick out certain horizons, the "diagnostic horizons", for the definition; examples are the World Reference Base for Soil Resources (WRB), the USDA soil taxonomy and the Australian Soil Classification. Diagnostic horizons are usually indicated with names, e.g. the "cambic horizon" or the "spodic horizon". The WRB lists 40 diagnostic horizons. In addition to these diagnostic horizons, some other soil characteristics may be needed to define a soil type. Some soils do not have a clear development of horizons.
A soil horizon is a result of soil-forming processes (pedogenesis). Layers that have not undergone such processes may be simply called "layers".
Horizon sequence
Many soils have an organic surface layer, which is denominated with a capital letter "O" (letters may differ depending on the system). The mineral soil usually starts with an A horizon. If a well-developed subsoil horizon as a result of soil formation exists, it is generally called a B horizon. An underlying loose, but poorly developed horizon is called a C horizon. Hard bedrock is mostly denominated R. Most individual systems defined more horizons and layers than just these five. In the following, the horizons and layers are listed more or less by their position from top to bottom within the soil profile. Not all of them are present in every soil. | Soil horizon | Wikipedia | 495 | 1522331 | https://en.wikipedia.org/wiki/Soil%20horizon | Physical sciences | Soil science | Earth science |
Soils with a history of human interference, for instance through major earthworks or regular deep ploughing, may lack distinct horizons almost completely. When examining soils in the field, attention must be paid to the local geomorphology and the historical uses to which the land has been put, in order to ensure that the appropriate names are applied to the observed horizons.
Examples of soil profiles
Horizons and layers according to the World Reference Base for Soil Resources
The designations are found in Chapter 10 of the World Reference Base for Soil Resources Manual, 4th edition (2022). The chapter starts with some general definitions:
The fine earth comprises the soil constituents ≤ 2 mm. The whole soil comprises fine earth, coarse fragments, artefacts, cemented parts, and dead plant residues of any size.
A litter layer is a loose layer that contains > 90% (by volume, related to the fine earth plus all dead plant residues) recognizable dead plant tissues (e.g. undecomposed leaves). Dead plant material still connected to living plants (e.g. dead parts of Sphagnum mosses) is not regarded to form part of a litter layer. The soil surface (0 cm) is by convention the surface of the soil after removing, if present, the litter layer and, if present, below a layer of living plants (e.g. living mosses). The mineral soil surface is the upper limit of the uppermost layer consisting of mineral material.
A soil layer is a zone in the soil, approximately parallel to the soil surface, with properties different from layers above and/or below it. If at least one of these properties is the result of soil-forming processes, the layer is called a soil horizon. In the following, the term layer is used to indicate the possibility that soil-forming processes did not occur. | Soil horizon | Wikipedia | 372 | 1522331 | https://en.wikipedia.org/wiki/Soil%20horizon | Physical sciences | Soil science | Earth science |
The following layers are distinguished (see Chapter 3.3 of the WRB Manual):
Organic layers consist of organic material: Have ≥ 20% organic carbon, not consisting of artefacts (related to the fine earth plus the dead plant residues of any length and a diameter ≤ 5 mm) and do not form part of a litter layer.
Organotechnic layers consist of organotechnic material: Have ≥ 35% (by volume, related to the whole soil) artefacts containing ≥ 20% organic carbon; and < 20% organic carbon, not consisting of artefacts (related to the fine earth plus the dead plant residues of any length and a diameter ≤ 5 mm).
Mineral layers are all other layers.
The designation consists of a capital letter (master symbol), which in most cases is followed by one or more lowercase letters (suffixes).
Master symbols
H:
Organic or organotechnic layer, not forming part of a litter layer;
water saturation > 30 consecutive days in most years or drained;
generally regarded as peat layer or organic limnic layer.
O:
Organic horizon or organotechnic layer, not forming part of a litter layer;
water saturation ≤ 30 consecutive days in most years and not drained;
generally regarded as non-peat and non-limnic horizon.
A:
Mineral horizon at the mineral soil surface or buried;
contains organic matter that has at least partly been modified in-situ;
soil structure and/or structural elements created by cultivation in ≥ 50% (by volume, related to the fine earth), i.e. rock structure, if present, in < 50% (by volume).
E:
Mineral horizon;
has lost by downward movement within the soil (vertically or laterally) one or more of the following: Fe, Al, and/or Mn species; clay minerals; organic matter.
B:
Mineral horizon that has (at least originally) formed below an A or E horizon;
rock structure, if present, in < 50% (by volume, related to the fine earth);
one or more of the following processes of soil formation:
formation of soil aggregate structure
formation of clay minerals and/or oxides
accumulation by illuviation processes of one or more of the following: Fe, Al, and/or Mn species; clay minerals; organic matter; silica; carbonates; gypsum
removal of carbonates or gypsum.
B horizons may show other accumulations as well. | Soil horizon | Wikipedia | 498 | 1522331 | https://en.wikipedia.org/wiki/Soil%20horizon | Physical sciences | Soil science | Earth science |
C:
Mineral layer;
unconsolidated (can be cut with a spade when moist), or consolidated and more fractured than the R layer;
no soil formation, or soil formation that does not meet the criteria of the A, E, and B horizon.
R:
Consolidated rock;
air-dry or drier specimens, when placed in water, will not slake within 24 hours;
fractures, if present, occupy < 10% (by volume, related to the whole soil);
not resulting from the cementation of a soil horizon.
I:
≥ 75% ice (by volume, related to the whole soil), permanent, below an H, O, A, E, B or C layer.
W:
Permanent water above the soil surface or between layers, may be seasonally frozen.
Suffixes
This is the list of suffixes to the master symbols. In brackets is indicated to which master symbols the suffixes can be added. The suffixes e and i have different meanings for organic and mineral layers. | Soil horizon | Wikipedia | 207 | 1522331 | https://en.wikipedia.org/wiki/Soil%20horizon | Physical sciences | Soil science | Earth science |
a: Organic material in an advanced state of decomposition [a like advanced] (H, O).
b: Buried horizon; first, the horizon has formed, and then, it was buried by mineral material [b like buried] (H, O, A, E, B).
c: Concretions and/or nodules [c like concretion]; only used if following another suffix (k, q, v, y) that indicates the accumulated substance.
d: Drained [d like drained] (H).
e: Organic material in an intermediate state of decomposition [e like intermediate] (H, O).
e: Saprolite [e like saprolite] (C).
f: Permafrost [f like frost] (H, O, A, E, B, C).
g: Accumulation of Fe and/or Mn oxides predominantly inside soil aggregates, if present, and loss of these oxides on aggregate surfaces (A, B, C), or loss of Fe and/or Mn by lateral subsurface flow and pale colours in ≥ 50% of the exposed area (E); transport in reduced form [g like stagnic].
h: Significant amount of organic matter; in A horizons at least partly modified in situ; in B horizons predominantly by illuviation; in C horizons forming part of the parent material [h like humus] (A, B, C).
i: Organic material in an initial state of decomposition; [i like initial] (H, O).
j: Accumulation of jarosite and/or schwertmannite [j like jarosite] (H, O, A, E, B, C).
k: Accumulation of secondary carbonates [k like German Karbonat] (H, O, A, E, B, C).
l: Accumulation of Fe and/or Mn in reduced form by upward-moving capillary water with subsequent oxidation: accumulation predominantly at soil aggregate surfaces, if present, and reduction of these oxides inside the aggregates [l like capillary] (H, A, B, C).
m: Pedogenic cementation in ≥ 50% of the volume; cementation class: at least moderately cemented; only used if following another suffix (k, l, q, s, v, y, z) that indicates the cementing agent [m like cemented]. | Soil horizon | Wikipedia | 511 | 1522331 | https://en.wikipedia.org/wiki/Soil%20horizon | Physical sciences | Soil science | Earth science |
n: Exchangeable sodium percentage ≥ 6% [n like natrium] (E, B, C).
o: Residual accumulation of large amounts of pedogenic oxides in strongly weathered horizons [o like oxide] (B).
p: Modification by cultivation (e.g. ploughing); mineral layers are designated A, even if they belonged to another layer before cultivation [p like plough] (H, O, A).
q: Accumulation of secondary silica [q like quartz] (A, E, B, C).
r: Strong reduction [r like reduction] (A, E, B, C).
s: Accumulation of Fe oxides, Mn oxides and/or Al by vertical illuviation processes from above [s like sesquioxide]. (B, C).
ss: Slickensides and/or wedge-shaped aggregates [ss like "s"licken"s"ide] (B).
t: Accumulation of clay minerals by illuviation processes [t like German Ton, clay]. (B, C).
u: Containing artefacts or consisting of artefacts [u like urban] (H, O, A, E, B, C, R).
v: Plinthite [the suffix v has no connotation] (B, C).
w: Formation of soil structure and/or oxides and/or clay minerals (layer silicates, allophanes and/or imogolites) [w like weathered] (B).
x: Fragic characteristics [the x refers to the impossibility of roots to enter the aggregates] (E, B, C).
y: Accumulation of secondary gypsum [y like gypsum or Spanish yeso] (A, E, B, C).
z: Presence of readily soluble salts [z like Dutch zout] (H, O, A, E, B, C).
@: cryogenic alteration (H, O, A, E, B, C).
α: Presence of primary carbonates (in R layers related to the rock, in all other layers related to the fine earth) [α like carbonate] (H, A, E, B, C, R).
β: Bulk density ≤ 0.9 kg dm-3 [β like bulk density] (B). | Soil horizon | Wikipedia | 500 | 1522331 | https://en.wikipedia.org/wiki/Soil%20horizon | Physical sciences | Soil science | Earth science |
γ: Containing ≥ 5% (by grain count) volcanic glasses in the fraction between > 0.02 and ≤ 2 mm [γ like glass] (H, O, A, E, B, C).
δ: High bulk density (natural or anthropogenic), so that roots cannot enter, except along cracks [δ like dense] (A, E, B, C).
λ: Deposited in a body of water (limnic) [λ like limnic] (H, A. C).
ρ: Relict features (only used if following another suffix (g, k, l, p, r, @) that indicates the relict feature) [ρ like relict].
σ: Permanent water saturation and no redoximorphic features [σ like saturation] (A, D, B, C)
τ: Human-transported natural material (related to the whole soil) [τ like transported] ((H, O, A, B, C).
φ: Accumulation of Fe and/or Mn in reduced form by lateral subsurface flow with subsequent oxidation [φ like flow] (A, B, C). | Soil horizon | Wikipedia | 242 | 1522331 | https://en.wikipedia.org/wiki/Soil%20horizon | Physical sciences | Soil science | Earth science |
I and W layers have no suffixes.
Combination of suffixes:
1. The c follows the suffix that indicates the substance that forms the concretions or nodules; if this is true for more than one suffix, each one is followed by the c.
2. The m follows the suffix that indicates the substance that is the cementing agent; if this is true for more than one suffix, each one is followed by the m.
3. The ρ follows the suffix that indicates the relict features; if this is true for more than one suffix, each one is followed by the ρ.
4. If two suffixes belong to the same soil-forming process, they follow each other immediately; in the combination of t and n, the t is written first; rules 1, 2 and 3 have to be followed, if applicable.
Examples: Btn, Bhs, Bsh, Bhsm, Bsmh.
5. If in a B horizon the characteristics of the suffixes g, h, k, l, o, q, s, t, v, or y are strongly expressed, the suffix w is not used, even if its characteristics are present; if the characteristics of the mentioned suffixes are weakly expressed and the characteristics of the suffix w are present as well, the suffixes are combined.
6. In H and O layers, the i, e or a is written first.
7. The @, f and b are written last, if b occurs together with @ or f (only if other suffixes are present as well): @b, fb.
8. Besides that, combinations must be in the sequence of dominance, the dominant one first. Examples: Btng, Btgb, Bkcyc.
Transitional layers
If the characteristics of two or more master layers are superimposed to each other, the master symbols are combined without anything in between, the dominant one first, each one followed by its suffixes.
Examples: AhBw, BwAh, AhE, EAh, EBg, BgE, BwC, CBw, BsC, CBs. | Soil horizon | Wikipedia | 431 | 1522331 | https://en.wikipedia.org/wiki/Soil%20horizon | Physical sciences | Soil science | Earth science |
If the characteristics of two or more master layers occur in the same depth range, but occupy distinct parts clearly separated from each other, the master symbols are combined with the slash (/), the dominant one first, each one followed by its suffixes.
Examples:
Bt/E (interfingering of E material into a Bt horizon),
C/Bt (Bt horizon forming lamellae within a C layer).
W cannot be combined with other master symbols. H, O, I, and R can only be combined using the slash.
Layer sequences
The sequence of the layers is from top to down with a hyphen in between.
If lithic discontinuities occur, the strata are indicated by preceding figures, starting with the second stratum. I and W layers are not considered as strata. All layers of the respective stratum are indicated by the figure:
Example: Oi-Oe-Ah-E-2Bt-2C-3R.
If two or more layers with the same designation occur, the letters are followed by figures. The sequence of figures continues across different strata.
Examples:
Oi-Oe-Oa-Ah-Bw1-Bw2-2Bw3-3Ahb1-3Eb-3Btb-4Ahb2-4C,
Oi-He-Ha-Cr1-2Heb-2Hab-2Cr2-3Crγ.
Horizons and layers according to the FAO Guidelines for Soil Description (2006)
Source:
Master horizons and layers
H horizons or layers:
These are layers of organic material. Organic material is defined by having a certain minimum content of soil organic carbon. In the WRB, this is 20% (by weight). The H horizon is formed from organic residues that are not incorporated into the mineral soil. The residues may be partially altered by decomposition. Contrary to the O horizons, the H horizons are saturated with water for prolonged periods, or were once saturated but are now drained artificially. In many H horizons, the residues are predominantly mosses. Although these horizons form above the mineral soil surface, they may be buried by mineral soil and therefore be found at greater depth. H horizons may be overlain by O horizons that especially form after drainage. | Soil horizon | Wikipedia | 466 | 1522331 | https://en.wikipedia.org/wiki/Soil%20horizon | Physical sciences | Soil science | Earth science |
O horizons or layers:
These are layers of organic material. Organic material is defined by having a certain minimum content of soil organic carbon. In the WRB, this is 20% (by weight). The O horizon is formed from organic residues that are not incorporated into the mineral soil. The residues may be partially altered by decomposition. Contrary to the H horizons, the O horizons are not saturated with water for prolonged periods and not drained artificially. In many O horizons, the residues are leaves, needles, twigs, moss, and lichens. Although these horizons form above the mineral soil surface, they may be buried by mineral soil and therefore be found at greater depth.
A horizons:
These are mineral horizons that formed at the surface or below an O horizon. All or much of the original rock structure has been obliterated. Additionally, they are characterized by one or more of the following:
an accumulation of humified organic matter, intimately mixed with the mineral fraction, and not displaying properties characteristic of E or B horizons (see below);
properties resulting from cultivation, pasturing, or similar kinds of disturbance;
a morphology that is different from the underlying B or C horizon, resulting from processes related to the surface.
If a surface horizon has properties of both A and E horizons but the dominant feature is an accumulation of humified organic matter, it is designated an A horizon.
E horizons:
These are mineral horizons in which the main feature is loss of clay minerals, iron, aluminium, organic matter or some combination of these, leaving a concentration of sand and silt particles. However, pedogenesis is advanced, because the lost substances first have been formed or accumulated there. All or much of the original rock structure is obliterated. An E horizon is usually, but not necessarily, lighter in colour than an underlying B horizon. In some soils, the colour is that of the sand and silt particles. An E horizon is most commonly differentiated from an underlying B horizon: by colour of higher value or lower chroma, or both; by coarser texture; or by a combination of these properties. An E horizon is commonly near to the surface, below an O or A horizon, and above a B horizon. However, the symbol E may be used without regard to the position in the profile for any horizon that meets the requirements and that has resulted from soil genesis. | Soil horizon | Wikipedia | 481 | 1522331 | https://en.wikipedia.org/wiki/Soil%20horizon | Physical sciences | Soil science | Earth science |
B horizons:
These are horizons that formed below an A, E, H, or O horizon, and in which the dominant features are the obliteration of all or much of the original rock structure, together with one or a combination of the following:
residual concentration of oxides (especially iron oxides) and/or clay minerals;
evidence of removal of carbonates or gypsum;
illuvial concentration, alone or in combination, of clay minerals, iron, aluminium, organic matter, carbonates, gypsum or silica;
coatings of oxides that make the horizon conspicuously lower in value, higher in chroma, or redder in hue than overlying and underlying horizons without apparent illuviation of iron;
alteration that forms clay minerals or liberates oxides or both and that forms a granular, blocky or prismatic structure if volume changes accompany changes in moisture content;
brittleness.
All kinds of B horizons are or were originally subsurface horizons.
Examples of layers that are not B horizons are: layers in which clay films either coat rock fragments or are found on finely stratified unconsolidated sediments, whether the films were formed in place or by illuviation; layers into which carbonates have been illuviated but that are not contiguous to an overlying genetic horizon; and layers with gleying but no other pedogenic changes. | Soil horizon | Wikipedia | 289 | 1522331 | https://en.wikipedia.org/wiki/Soil%20horizon | Physical sciences | Soil science | Earth science |
C horizons or layers:
These are horizons or layers, excluding hard bedrock, that are little affected by pedogenic processes and lack properties of H, O, A, E or B horizons. Most are mineral layers, but some siliceous and calcareous layers, such as shells, coral, and diatomaceous earth, are included. The material of C layers may be either like or unlike that from which the overlying solum presumably formed. Plant roots can penetrate C horizons, which provide an important growing medium. Included as C layers are sediments, saprolite, non-indurated bedrock, and other geological materials that commonly slake within 24 hours when air-dry or drier chunks are placed in water, and that, when moist, can be dug with a spade. Some soils form in material that is already highly weathered, and if such material does not meet the requirements of A, E, or B horizons, it is designated C. Changes not considered pedogenic are those not related to overlying horizons. Layers having accumulations of silica, carbonates, or gypsum, even if indurated, may be included in C horizons, unless the layer is obviously affected by pedogenic processes; then it is a B horizon.
R layers:
These consist of hard bedrock underlying the soil. Granite, basalt, quartzite, and indurated limestone or sandstone are examples of bedrock that are designated R. Air-dry or drier chunks of an R layer, when placed in water, will not slake within 24 hours. The R layer is sufficiently coherent when moist to make hand digging with a spade impractical. The bedrock may contain cracks, but these are so few and so small that few roots can penetrate. The cracks may be coated or filled with soil material.
I layers:
These are ice lenses and wedges that contain at least 75 per cent ice (by volume) and that distinctly separate layers (organic or mineral) in the soil.
L layers:
These are sediments deposited in a body of water. They may be organic or mineral. Limnic material is either: (i) deposited by precipitation or through action of aquatic organisms, such as algae, especially diatoms; or (ii) derived from underwater and floating aquatic plants and subsequently modified by aquatic animals. L layers include coprogenous earth or sedimentary peat (mostly organic), diatomaceous earth (mostly siliceous), and marl (mostly calcareous). | Soil horizon | Wikipedia | 509 | 1522331 | https://en.wikipedia.org/wiki/Soil%20horizon | Physical sciences | Soil science | Earth science |
W layers:
These are either water layers in soils or water layers submerging soils. The water is present either permanently or cyclic within the time frame of 24 hours. Some organic soils float on water. In other cases, shallow water (i.e. water not deeper than 1 m) may cover the soil permanently, as in the case of shallow lakes, or cyclic, as in tidal flats. The occurrence of tidal water can be indicated by the letter W in brackets: (W).
Transitional horizons and layers
A horizon that combines the characteristics of two master horizons is indicated with both capital letters, the dominant one written first. Example: AB and BA. If discrete, intermingled bodies of two master horizons occur together, the horizon symbols are combined using a slash (/). Example: A/B and B/A. The master horizon symbols may be followed by the lowercase letters indicating subordinate characteristics (see below). Example: AhBw. The I, L and W symbols are not used in transitional horizon designations.
Subordinate characteristics
This is the list of suffixes to the master horizons. After the hyphen, it is indicated to which master horizons the suffixes can be added. | Soil horizon | Wikipedia | 244 | 1522331 | https://en.wikipedia.org/wiki/Soil%20horizon | Physical sciences | Soil science | Earth science |
a: Highly decomposed organic material—H and O horizons.
b: Buried genetic horizon—mineral horizons, not cryoturbated.
c: Concretions or nodules—mineral horizons.
c: Coprogenous earth—L horizon.
d: Dense layer (physically root restrictive)—mineral horizons, not with m.
d: Diatomaceous earth—L horizon.
e: Moderately decomposed organic material—H and O horizons.
f: Frozen soil—not in I and R horizons.
g: Stagnic conditions—no restriction.
h: Accumulation of organic matter—mineral horizons.
i: Slickensides—mineral horizons.
i: Slightly decomposed organic material—H and O horizons.
j: Jarosite accumulation—no restriction.
k: Accumulation of pedogenic carbonates—no restriction.
l: Mottling due to upmoving groundwater (gleying)—no restriction.
m: Strong cementation or induration (pedogenic, massive)—mineral horizons.
m: Marl—L horizon.
n: Pedogenic accumulation of exchangeable sodium—no restriction.
o: Residual accumulation of sesquioxides (pedogenic)—no restriction.
p: Ploughing or other human disturbance—no restriction; ploughed E, B, or C horizons are referred to as Ap.
q: Accumulation of pedogenic silica—no restriction.
r: Strong reduction—no restriction.
s: Illuvial accumulation of sesquioxides—B horizons.
t: Illuvial accumulation of clay minerals—B and C horizons.
u: Urban and other human-made materials (artefacts—H, O, A, E, B and C horizons.
v: Occurrence of plinthite—no restriction.
w: Development of colour or structure—B horizons.
x: Fragipan characteristics—no restriction.
y: Pedogenic accumulation of gypsum—no restriction.
z: Pedogenic accumulation of salts more soluble than gypsum—no restriction.
@: Evidence of cryoturbation—no restriction. | Soil horizon | Wikipedia | 441 | 1522331 | https://en.wikipedia.org/wiki/Soil%20horizon | Physical sciences | Soil science | Earth science |
Discontinuities and vertical subdivisions
Numerical prefixes are used to denote lithic discontinuities. By convention, 1 is not shown. Numerical suffixes are used to denote subdivisions within a horizon. The horizons in a profile are combined using a hyphen (-). Example: Ah-E-Bt1-2Bt2-2BwC-3C1-3C2.
Horizons and layers according to the USDA Field Book for Describing and Sampling Soils (2012)
Source:
Master horizons and layers
O: Organic soil materials (not limnic).
A: Mineral; organic matter (humus) accumulation.
E: Mineral; some loss of Fe, Al, clay, or organic matter.
B: Subsurface accumulation of clay, Fe, Al, Si, humus, CaCO3, CaSO4; or loss of CaCO3; or accumulation of sesquioxides; or subsurface soil structure.
C: Little or no pedogenic alteration, unconsolidated earthy material, soft bedrock.
L: Limnic soil materials.
W: A layer of liquid water (W) or permanently frozen water (Wf) within or beneath the soil (excludes water/ice above soil).
M: Root-limiting subsoil layers of human-manufactured materials.
R: Bedrock, strongly cemented to indurated.
Transitional horizons and layers
A horizon that combines the characteristics of two master horizons is indicated with both capital letters, the dominant one written first. Example: AB and BA. If discrete, intermingled bodies of two master horizons occur together, the horizon symbols are combined using a slash (/). Example: A/B and B/A. | Soil horizon | Wikipedia | 354 | 1522331 | https://en.wikipedia.org/wiki/Soil%20horizon | Physical sciences | Soil science | Earth science |
Horizon suffixes
a: Highly decomposed organic matter (used only with O).
aa: (proposed) Accumulation of anhydrite (CaSO4).
b: Buried genetic horizon (not used with C horizons).
c: Concretions or nodules.
co: Coprogenous earth (used only with L).
d: Densic layer (physically root restrictive).
di: Diatomaceous earth (used only with L).
e: Moderately decomposed organic matter (used only with O).
f: Permanently frozen soil or ice (permafrost); continuous subsurface ice; not seasonal ice.
ff: Permanently frozen soil ("dry" permafrost); no continuous ice; not seasonal ice.
g: Strong gley.
h: Illuvial organic matter accumulation.
i: Slightly decomposed organic matter (used only with O).
j: Jarosite accumulation.
jj: Evidence of cryoturbation.
k: Pedogenic CaCO3 accumulation (<50% by vol.).
kk: Major pedogenic CaCO3 accumulation (≥50% by vol.).
m: Continuous cementation (pedogenic).
ma: Marl (used only with L).
n: Pedogenic, exchangeable sodium accumulation.
o: Residual sesquioxide accumulation (pedogenic).
p: Plow layer or other artificial disturbance.
q: Secondary (pedogenic) silica accumulation.
r: Weathered or soft bedrock.
s: Illuvial sesquioxide and organic matter accumulation.
se: Presence of sulfides (in mineral or organic horizons).
ss: Slickensides.
t: Illuvial accumulation of silicate clay.
u: Presence of human-manufactured materials (artifacts).
v: Plinthite.
w: Weak color or structure within B (used only with B).
x: Fragipan characteristics.
y: Accumulation of gypsum.
yy: Dominance of gypsum (≈≥50% by vol.).
z: Pedogenic accumulation of salt more soluble than gypsum. | Soil horizon | Wikipedia | 452 | 1522331 | https://en.wikipedia.org/wiki/Soil%20horizon | Physical sciences | Soil science | Earth science |
Other horizon modifiers
Numerical prefixes are used to denote lithologic discontinuities. By convention, 1 is not shown. Numerical suffixes are used to denote subdivisions within a master horizon. Example: A, E, Bt1, 2Bt2, 2BC, 3C1, 3C2.
Horizons according to the Australian Soil and Land Survey Field Handbook (2009)
Source:
Horizons
O horizon
The "O" stands for organic matter. It is a surface layer, dominated by the presence of large amounts of organic matter in varying stages of decomposition. In the Australian system, the O horizon should be considered distinct from the layer of leaf litter covering many heavily vegetated areas, which contains no weathered mineral particles and is not part of the soil itself. O horizons may be divided into O1 and O2 categories, whereby O1 horizons contain undecomposed matter whose origin can be spotted on sight (for instance, fragments of leaves), and O2 horizons contain organic debris in various stages of decomposition, the origin of which is not readily visible. O horizons contain ≥ 20% organic carbon.
P horizon
These horizons are also heavily organic but are distinct from O horizons in that they form under waterlogged conditions. The "P" designation comes from their common name, peats. They may be divided into P1 and P2 in the same way as O horizons. P horizons contain ≥ 12 to 18% organic carbon, depending on the clay content.
A horizon | Soil horizon | Wikipedia | 301 | 1522331 | https://en.wikipedia.org/wiki/Soil%20horizon | Physical sciences | Soil science | Earth science |
The A horizon is the top layer of the mineral soil horizons, often referred to as 'topsoil'. This layer contains dark decomposed organic matter, which is called "humus". The technical definition of an A horizon may vary between the systems, but it is most commonly described in terms relative to deeper layers. "A" horizons may be darker in colour than deeper layers and contain more organic matter, or they may be lighter but contain less clay or pedogenic oxides. The A is a surface horizon, and as such is also known as the zone in which most biological activity occurs. Soil organisms such as earthworms, potworms (enchytraeids), arthropods, nematodes, fungi, and many species of bacteria and archaea are concentrated here, often in close association with plant roots. Thus, the A horizon may be referred to as the biomantle. However, since biological activity extends far deeper into the soil, it cannot be used as a chief distinguishing feature of an A horizon. The A horizon may be further subdivided into A1 (dark, maximum biologic activity), A2 (paler), and A3 (transitional to the B horizon).
E horizon (not used in the Australian system)
"E", being short for eluviated, is most commonly used to label a horizon that has been significantly leached of its mineral and/or organic content, leaving a pale layer largely composed of silicates or silica. These are present only in older, well-developed soils, and generally occur between the A and B horizons. In systems where (like in the Australian system) this designation is not employed, leached layers are classified firstly as an A or B according to other characteristics, and then appended with the designation "e" (see the section below on horizon suffixes). In soils that contain gravels, due to animal bioturbation, a stonelayer commonly forms near or at the base of the E horizon.
B horizon | Soil horizon | Wikipedia | 415 | 1522331 | https://en.wikipedia.org/wiki/Soil%20horizon | Physical sciences | Soil science | Earth science |
The B horizon is commonly referred to as "subsoil" and consists of mineral layers which are significantly altered by pedogenesis, mostly with the formation of iron oxides and clay minerals. It is usually brownish or reddish due to the iron oxides, which increases the chroma of the subsoil to a degree that it can be distinguished from the other horizons. The weathering may be biologically mediated. In addition, the B horizon is defined as having a distinctly different structure or consistency than the horizon(s) above and the horizon(s) below.
The B horizon can also accumulate minerals and organic matter that are migrating downwards from the A and E horizons. If so, this layer is also known as the illuviated or illuvial horizon.
As with the A horizon, the B horizon may be divided into B1, B2, and B3 types under the Australian system. B1 is a transitional horizon of the opposite nature to an A3 – dominated by the properties of the B horizons below it, but containing some A-horizon characteristics. B2 horizons have a high concentration of clay minerals or oxides. B3 horizons are transitional between the overlying B layers and the material beneath it, whether C or D horizon.
The A3, B1, and B3 horizons are not tightly defined, and their use is generally at the discretion of the individual worker.
Plant roots penetrate throughout this layer, but it has very little humus.
The A/E/B horizons are referred to collectively as the "solum", the surface depth of the soil where biologically activity and climate effects drives pedogenesis. The layers below the solum have no collective name but are distinct in that they are noticeably less affected by surface soil-forming processes.
C horizon
The C horizon is below the solum horizons. This layer is little affected by pedogenesis. Clay illuviation, if present, is not significant. The absence of solum-type development (pedogenesis) is one of the defining attributes. The C horizon forms either in deposits (e.g., loess, flood deposits, landslides) or it formed from weathering of residual bedrock. The C horizon may be enriched with carbonates carried below the solum by leaching. If there is no lithologic discontinuity between the solum and the C horizon and no underlying bedrock present, the C horizon resembles the parent material of the solum.
D horizon | Soil horizon | Wikipedia | 509 | 1522331 | https://en.wikipedia.org/wiki/Soil%20horizon | Physical sciences | Soil science | Earth science |
D horizons are not universally distinguished, but in the Australian system refer to "any soil material below the solum that is unlike the solum in its general character, is not C horizon, and cannot be given reliable horizon designation… [it] may be recognized by the contrast in pedologic organization between it and the overlying horizons" (National Committee on Soil and Terrain, 2009, p. 151).
R horizon
R horizons denote the layer of partially weathered or unweathered bedrock at the base of the soil profile. Unlike the above layers, R horizons largely comprise continuous masses (as opposed to boulders) of hard rock that cannot be excavated by hand. If there is no lithologic discontinuity between the solum and the R horizon, the R horizon resembles the parent material of the solum.
L horizon (not used in the Australian system)
L (Limnic) horizons or layers indicate mineral or organic material that has been deposited in water by precipitation or through the actions of aquatic organisms. Included are coprogenous earth (sedimentary peat), diatomaceous earth, and marl; and is usually found as a remnant of past bodies of standing water.
Transitional horizons
A horizon that combines the characteristics of two horizons is indicated with both capital letters, the dominant one written first. Example: AB and BA. If distinct parts have properties of two kinds of horizons, the horizon symbols are combined using a slash (/). Example: A/B and B/A.
Horizon suffixes
In addition to the main descriptors above, several modifiers exist to add necessary detail to each horizon. Firstly, each major horizon may be divided into sub-horizons by the addition of a numerical subscript, based on minor shifts in colour or texture with increasing depth (e.g., B21, B22, B23 etc.). While this can add necessary depth to a field description, workers should bear in mind that excessive division of a soil profile into narrow sub-horizons should be avoided. Walking as little as ten metres in any direction and digging another hole can often reveal a very different profile in regards to the depth and thickness of each horizon. Over-precise description can be a waste of time. In the Australian system, as a rule of thumb, layers thinner than 5 cm (2 inches) or so are best described as pans or segregations within a horizon rather than as a distinct layer. | Soil horizon | Wikipedia | 492 | 1522331 | https://en.wikipedia.org/wiki/Soil%20horizon | Physical sciences | Soil science | Earth science |
Suffixes describing particular features of a horizon may also be added. The Australian system provides the following suffixes:
b: buried horizon.
c: presence of mineral concretions or nodules, perhaps of iron, aluminium, or manganese.
d: root restricting layer.
e: conspicuously bleached.
f: faunal accumulations in A horizons.
g: gleyed horizon.
h: accumulation of organic matter.
j: sporadically bleached.
k: accumulation of carbonates, commonly calcium carbonate.
m: strong cementation or induration.
p: disturbed by ploughing or other tillage practices (A horizons only).
q: accumulation of secondary silica.
r: weathered, digable rock.
s: sesquioxide accumulation.
t: accumulation of clay minerals.
w: weak development.
x: fragipan.
y: accumulation of calcium sulfate (gypsum).
z: accumulation of salts more soluble than calcium sulfate.
Buried soils
Soil formation is often described as occurring in situ: Rock breaks down, weathers and is mixed with other materials, or loose sediments are transformed by weathering. But the process is often far more complicated. For instance, a fully formed profile may have developed in an area only to be buried by wind- or water-deposited sediments which later formed into another soil profile. This sort of occurrence is most common in coastal areas, and descriptions are modified by numerical prefixes. Thus, a profile containing a buried sequence could be structured O, A1, A2, B2, 2A2, 2B21, 2B22, 2C with the buried profile commencing at 2A2.
Diagnostic soil horizons
Many soil classification systems have diagnostic horizons. A diagnostic horizon is a horizon used to define soil taxonomic units (e.g., to define soil types). A taxonomic unit is determined by the presence or absence of one or more diagnostic horizons in a required depth. In addition, most classification systems use other soil characteristics to define taxonomic units. The diagnostic horizons need to be thoroughly characterized by a set of criteria. When allocating soil (a pedon, a soil profile) to a taxonomic unit, one has to check every horizon of this soil and decide whether or not the horizon fulfills the criteria of a diagnostic horizon. Based on the identified diagnostic horizons, one can proceed with the allocation of the soil to a taxonomic unit. The following lists the diagnostic horizons of two soil classification systems. | Soil horizon | Wikipedia | 497 | 1522331 | https://en.wikipedia.org/wiki/Soil%20horizon | Physical sciences | Soil science | Earth science |
Diagnostic horizons in the World Reference Base for Soil Resources (WRB)
Source:
Albic horizon
Anthraquic horizon
Argic horizon
Calcic horizon
Cambic horizon
Chernic horizon
Cohesic horizon
Cryic horizon
Duric horizon
Ferralic horizon
Ferric horizon
Folic horizon
Fragic horizon
Gypsic horizon
Histic horizon
Hortic horizon
Hydragric horizon
Irragric horizon
Limonic horizon
Mollic horizon
Natric horizon
Nitic horizon
Panpaic horizon
Petrocalcic horizon
Petroduric horizon
Petrogypsic horizon
Petroplinthic horizon
Pisoplinthic horizon
Plaggic horizon
Plinthic horizon
Pretic horizon
Protovertic horizon
Salic horizon
Sombric horizon
Spodic horizon
Terric horizon
Thionic horizon
Tsitelic horizon
Umbric horizon
Vertic horizon
Diagnostic horizons in the USDA soil taxonomy (ST)
Source:
Diagnostic surface horizons
Anthropic epipedon
Folistic epipedon
Histic epipedon
Melanic epipedon
Mollic epipedon (see Mollisols)
Ochric epipedon
Plaggen epipedon
Umbric epipedon
Diagnostic subsurface horizons
Agric horizon
Albic horizon
Anhydric horizon
Argillic horizon
Calcic horizon
Cambic horizon
Duripan layer
Fragipan layer
Glossic horizon
Gypsic horizon
Kandic horizon
Natric horizon
Nitic horizon
Ortstein layer
Oxic horizon
Petrocalcic Horizon
Petrogypsic horizon
Petroplinthic horizon
Placic horizon
Salic horizon
Sombric horizon
Spodic horizon | Soil horizon | Wikipedia | 324 | 1522331 | https://en.wikipedia.org/wiki/Soil%20horizon | Physical sciences | Soil science | Earth science |
A fracture is any separation in a geologic formation, such as a joint or a fault that divides the rock into two or more pieces. A fracture will sometimes form a deep fissure or crevice in the rock. Fractures are commonly caused by stress exceeding the rock strength, causing the rock to lose cohesion along its weakest plane. Fractures can provide permeability for fluid movement, such as water or hydrocarbons. Highly fractured rocks can make good aquifers or hydrocarbon reservoirs, since they may possess both significant permeability and fracture porosity.
Brittle deformation
Fractures are forms of brittle deformation. There are two types of primary brittle deformation processes. Tensile fracturing results in joints. Shear fractures are the first initial breaks resulting from shear forces exceeding the cohesive strength in that plane.
After those two initial deformations, several other types of secondary brittle deformation can be observed, such as frictional sliding or cataclastic flow on reactivated joints or faults.
Most often, fracture profiles will look like either a blade, ellipsoid, or circle.
Causes
Fractures in rocks can be formed either due to compression or tension. Fractures due to compression include thrust faults. Fractures may also be a result from shear or tensile stress. Some of the primary mechanisms are discussed below.
Modes
First, there are three modes of fractures that occur (regardless of mechanism):
Mode I crack – Opening mode (a tensile stress normal to the plane of the crack)
Mode II crack – Sliding mode (a shear stress acting parallel to the plane of the crack and perpendicular to the crack front)
Mode III crack – Tearing mode (a shear stress acting parallel to the plane of the crack and parallel to the crack front)
For more information on this, see fracture mechanics.
Tensile fractures
Rocks contain many pre-existing cracks where development of tensile fracture, or Mode I fracture, may be examined.
The first form is in axial stretching. In this case a remote tensile stress, σn, is applied, allowing microcracks to open slightly throughout the tensile region. As these cracks open up, the stresses at the crack tips intensify, eventually exceeding the rock strength and allowing the fracture to propagate. This can occur at times of rapid overburden erosion. Folding also can provide tension, such as along the top of an anticlinal fold axis. In this scenario the tensile forces associated with the stretching of the upper half of the layers during folding can induce tensile fractures parallel to the fold axis. | Fracture (geology) | Wikipedia | 510 | 6985160 | https://en.wikipedia.org/wiki/Fracture%20%28geology%29 | Physical sciences | Structural geology | Earth science |
Another, similar tensile fracture mechanism is hydraulic fracturing. In a natural environment, this occurs when rapid sediment compaction, thermal fluid expansion, or fluid injection causes the pore fluid pressure, σp, to exceed the pressure of the least principal normal stress, σn. When this occurs, a tensile fracture opens perpendicular to the plane of least stress.[4]
Tensile fracturing may also be induced by applied compressive loads, σn, along an axis such as in a Brazilian disk test. This applied compression force results in longitudinal splitting. In this situation, tiny tensile fractures form parallel to the loading axis while the load also forces any other microfractures closed. To picture this, imagine an envelope, with loading from the top. A load is applied on the top edge, the sides of the envelope open outward, even though nothing was pulling on them. Rapid deposition and compaction can sometimes induce these fractures.
Tensile fractures are almost always referred to as joints, which are fractures where no appreciable slip or shear is observed.
To fully understand the effects of applied tensile stress around a crack in a brittle material such a rock, fracture mechanics can be used. The concept of fracture mechanics was initially developed by A. A. Griffith during World War I. Griffith looked at the energy required to create new surfaces by breaking material bonds versus the elastic strain energy of the stretched bonds released. By analyzing a rod under uniform tension Griffith determined an expression for the critical stress at which a favorably orientated crack will grow. The critical stress at fracture is given by,
where γ = surface energy associated with broken bonds, E = Young's modulus, and a = half crack length. Fracture mechanics has generalized to that γ represents energy dissipated in fracture not just the energy associated with creation of new surfaces
Linear elastic fracture mechanics
Linear elastic fracture mechanics (LEFM) builds off the energy balance approach taken by Griffith but provides a more generalized approach for many crack problems. LEFM investigates the stress field near the crack tip and bases fracture criteria on stress field parameters. One important contribution of LEFM is the stress intensity factor, K, which is used to predict the stress at the crack tip. The stress field is given by | Fracture (geology) | Wikipedia | 451 | 6985160 | https://en.wikipedia.org/wiki/Fracture%20%28geology%29 | Physical sciences | Structural geology | Earth science |
where is the stress intensity factor for Mode I, II, or III cracking and is a dimensionless quantity that varies with applied load and sample geometry. As the stress field gets close to the crack tip, i.e. , becomes a fixed function of . With knowledge of the geometry of the crack and applied far field stresses, it is possible to predict the crack tip stresses, displacement, and growth. Energy release rate is defined to relate K to the Griffith energy balance as previously defined. In both LEFM and energy balance approaches, the crack is assumed to be cohesionless behind the crack tip. This provides a problem for geological applications such a fault, where friction exists all over a fault. Overcoming friction absorbs some of the energy that would otherwise go to crack growth. This means that for Modes II and III crack growth, LEFM and energy balances represent local stress fractures rather than global criteria.
Crack formation and propagation | Fracture (geology) | Wikipedia | 186 | 6985160 | https://en.wikipedia.org/wiki/Fracture%20%28geology%29 | Physical sciences | Structural geology | Earth science |
Cracks in rock do not form smooth path like a crack in a car windshield or a highly ductile crack like a ripped plastic grocery bag. Rocks are a polycrystalline material so cracks grow through the coalescing of complex microcracks that occur in front of the crack tip. This area of microcracks is called the brittle process zone. Consider a simplified 2D shear crack as shown in the image on the right. The shear crack, shown in blue, propagates when tensile cracks, shown in red, grow perpendicular to the direction of the least principal stresses. The tensile cracks propagate a short distance then become stable, allowing the shear crack to propagate. This type of crack propagation should only be considered an example. Fracture in rock is a 3D process with cracks growing in all directions. It is also important to note that once the crack grows, the microcracks in the brittle process zone are left behind leaving a weakened section of rock. This weakened section is more susceptible to changes in pore pressure and dilatation or compaction. Note that this description of formation and propagation considers temperatures and pressures near the Earth's surface. Rocks deep within the earth are subject to very high temperatures and pressures. This causes them to behave in the semi-brittle and plastic regimes which result in significantly different fracture mechanisms. In the plastic regime cracks acts like a plastic bag being torn. In this case stress at crack tips goes to two mechanisms, one which will drive propagation of the crack and the other which will blunt the crack tip. In the brittle-ductile transition zone, material will exhibit both brittle and plastic traits with the gradual onset of plasticity in the polycrystalline rock. The main form of deformation is called cataclastic flow, which will cause fractures to fail and propagate due to a mixture of brittle-frictional and plastic deformations.
Joint types
Describing joints can be difficult, especially without visuals. The following are descriptions of typical natural fracture joint geometries that might be encountered in field studies: | Fracture (geology) | Wikipedia | 419 | 6985160 | https://en.wikipedia.org/wiki/Fracture%20%28geology%29 | Physical sciences | Structural geology | Earth science |
Plumose Structures are fracture networks that form at a range of scales, and spread outward from a joint origin. The joint origin represents a point at which the fracture begins. The mirror zone is the joint morphology closest to the origin that results in very smooth surfaces. Mist zones exist on the fringe of mirror zones and represent the zone where the joint surface slightly roughens. Hackle zones predominate after mist zones, where the joint surface begins to get fairly rough. This hackle zone severity designates barbs, which are the curves away from the plume axis.
Orthogonal Joints occur when the joints within the system occur at mutually perpendicular angles to each other.
Conjugate Joints occur when the joints intersect each other at angles significantly less than ninety degrees.
Systematic Joints are joint systems in which all the joints are parallel or subparallel, and maintain roughly the same spacing from each other.
Columnar Joints are joints that cut the formation vertically in (typically) hexagonal columns. These tend to be a result of cooling and contraction in hypabyssal intrusions or lava flows.
Desiccation cracks are joints that form in a layer of mud when it dries and shrinks. Like columnar joints, these tend to be hexagonal in shape.
Sigmoidal Joints are joints that run parallel to each other, but are cut by sigmoidal (stretched S) joints in between.
Sheeting joints are joints that often form near surface, and as a result form parallel to the surface. These can also be recognized in exfoliation joints.
In joint systems where relatively long joints cut across the outcrop, the throughgoing joints act as master joints and the short joints that occur in between are cross joints.
Poisson effect is the creation of vertical contraction fractures that are a result of the relief of overburden over a formation.
Pinnate joints are joints that form immediately adjacent to and parallel to the shear face of a fault. These joints tend to merge with the faults at an angle between 35 and 45 degrees to the fault surface.
Release joints are tensile joints that form as a change in geologic shape results in the manifestation of local or regional tension that can create Mode I tensile fractures.
Concurrent joints that display a ladder pattern are interior regions with one set of joints that are fairly long, and the conjugate set of joints for the pattern remain relatively short, and terminate at the long joint.
Sometimes joints can also display grid patterns, which are fracture sets that have mutually crosscutting fractures. | Fracture (geology) | Wikipedia | 512 | 6985160 | https://en.wikipedia.org/wiki/Fracture%20%28geology%29 | Physical sciences | Structural geology | Earth science |
An en echelon or stepped array represents a set of tensile fractures that form within a fault zone parallel to each other. | Fracture (geology) | Wikipedia | 26 | 6985160 | https://en.wikipedia.org/wiki/Fracture%20%28geology%29 | Physical sciences | Structural geology | Earth science |
Faults and shear fractures
Faults are another form of fracture in a geologic environment. In any type of faulting, the active fracture experiences shear failure, as the faces of the fracture slip relative to each other. As a result, these fractures seem like large scale representations of Mode II and III fractures, however that is not necessarily the case.
On such a large scale, once the shear failure occurs, the fracture begins to curve its propagation towards the same direction as the tensile fractures. In other words, the fault typically attempts to orient itself perpendicular to the plane of least principal stress. This results in an out-of-plane shear relative to the initial reference plane. Therefore, these cannot necessarily be qualified as Mode II or III fractures.
An additional, important characteristic of shear-mode fractures is the process by which they spawn wing cracks, which are tensile cracks that form at the propagation tip of the shear fractures. As the faces slide in opposite directions, tension is created at the tip, and a mode I fracture is created in the direction of the σh-max, which is the direction of maximum principal stress.
Shear-failure criteria is an expression that attempts to describe the stress at which a shear rupture creates a crack and separation. This criterion is based largely off of the work of Charles Coulomb, who suggested that as long as all stresses are compressive, as is the case in shear fracture, the shear stress is related to the normal stress by:
σs= C+μ(σn-σf),
where C is the cohesion of the rock, or the shear stress necessary to cause failure given the normal stress across that plane equals 0. μ is the coefficient of internal friction, which serves as a constant of proportionality within geology. σn is the normal stress across the fracture at the instant of failure, σf represents the pore fluid pressure. It is important to point out that pore fluid pressure has a significant impact on shear stress, especially where pore fluid pressure approaches lithostatic pressure, which is the normal pressure induced by the weight of the overlying rock.
This relationship serves to provide the coulomb failure envelope within the Mohr-Coulomb Theory. | Fracture (geology) | Wikipedia | 449 | 6985160 | https://en.wikipedia.org/wiki/Fracture%20%28geology%29 | Physical sciences | Structural geology | Earth science |
Frictional sliding is one aspect for consideration during shear fracturing and faulting. The shear force parallel to the plane must overcome the frictional force to move the faces of the fracture across each other. In fracturing, frictional sliding typically only has significant effects on the reactivation on existing shear fractures. For more information on frictional forces, see friction.
The shear force required to slip fault is less than force required to fracture and create new faults as shown by the Mohr-Coulomb diagram. Since the earth is full of existing cracks and this means for any applied stress, many of these cracks are more likely to slip and redistribute stress than a new crack is to initiate. The Mohr's Diagram shown, provides a visual example. For a given stress state in the earth, if an existing fault or crack exists orientated anywhere from −α/4 to +α/4, this fault will slip before the strength of the rock is reached and a new fault is formed. While the applied stresses may be high enough to form a new fault, existing fracture planes will slip before fracture occurs.
One important idea when evaluating the friction behavior within a fracture is the impact of asperities, which are the irregularities that stick out from the rough surfaces of fractures. Since both faces have bumps and pieces that stick out, not all of the fracture face is actually touching the other face. The cumulative impact of asperities is a reduction of the real area of contact''', which is important when establishing frictional forces.
Subcritical crack growth
Sometimes, it is possible for fluids within the fracture to cause fracture propagation with a much lower pressure than initially required. The reaction between certain fluids and the minerals the rock is composed of can lower the stress required for fracture below the stress required throughout the rest of the rock. For instance, water and quartz can react to form a substitution of OH molecules for the O molecules in the quartz mineral lattice near the fracture tip. Since the OH bond is much lower than that with O, it effectively reduces the necessary tensile stress required to extend the fracture.
Engineering considerations
In geotechnical engineering a fracture forms a discontinuity that may have a large influence on the mechanical behavior (strength, deformation, etc.) of soil and rock masses in, for example, tunnel, foundation, or slope construction. | Fracture (geology) | Wikipedia | 478 | 6985160 | https://en.wikipedia.org/wiki/Fracture%20%28geology%29 | Physical sciences | Structural geology | Earth science |
Fractures also play a significant role in minerals exploitation. One aspect of the upstream energy sector is the production from naturally fractured reservoirs. There are a good number of naturally fractured reservoirs in the United States, and over the past century, they have provided a substantial boost to the nation's net hydrocarbon production.
The key concept is while low porosity, brittle rocks may have very little natural storage or flow capability, the rock is subjected to stresses that generate fractures, and these fractures can actually store a very large volume of hydrocarbons, capable of being recovered at very high rates. One of the most famous examples of a prolific naturally fractured reservoir was the Austin Chalk formation in South Texas. The chalk had very little porosity, and even less permeability. However, tectonic stresses over time created one of the most extensive fractured reservoirs in the world. By predicting the location and connectivity of fracture networks, geologists were able to plan horizontal wellbores to intersect as many fracture networks as possible. Many people credit this field for the birth of true horizontal drilling in a developmental context. Another example in South Texas is the Georgetown and Buda limestone formations.
Furthermore, the recent uprise in prevalence of unconventional reservoirs is actually, in part, a product of natural fractures. In this case, these microfractures are analogous to Griffith Cracks, however they can often be sufficient to supply the necessary productivity, especially after completions, to make what used to be marginally economic zones commercially productive with repeatable success.
However, while natural fractures can often be beneficial, they can also act as potential hazards while drilling wells. Natural fractures can have very high permeability, and as a result, any differences in hydrostatic balance down the well can result in well control issues. If a higher pressured natural fracture system is encountered, the rapid rate at which formation fluid can flow into the wellbore can cause the situation to rapidly escalate into a blowout, either at surface or in a higher subsurface formation. Conversely, if a lower pressured fracture network is encountered, fluid from the wellbore can flow very rapidly into the fractures, causing a loss of hydrostatic pressure and creating the potential for a blowout from a formation further up the hole.
Fracture modeling | Fracture (geology) | Wikipedia | 456 | 6985160 | https://en.wikipedia.org/wiki/Fracture%20%28geology%29 | Physical sciences | Structural geology | Earth science |
Since the mid-1980s, 2D and 3D computer modeling of fault and fracture networks has become common practice in Earth Sciences. This technology became known as "DFN" (discrete fracture network") modeling, later modified into "DFFN" (discrete fault and fracture network") modeling.
The technology consists of defining the statistical variation of various parameters such as size, shape, and orientation and modeling the fracture network in space in a semi-probabilistic way in two or three dimensions. Computer algorithms and speed of calculation have become sufficiently capable of capturing and simulating the complexities and geological variabilities in three dimensions, manifested in what became known as the "DMX Protocol".
Fracture terminology
A list of fracture related terms:asperities – tiny bumps and protrusions along the faces of fracturesaxial stretching – fracture mechanism resulting from a remote applied tensile force that creates fractures perpendicular to the tensile load axiscataclastic flow – microscopic ductile flow resulting from small grain-scale fracturing and frictional sliding distributed across a large area.*fracture – any surface of discontinuity within a layer of rockdike – a fracture filled with sedimentary or igneous rock not originating in the fracture formationfault – (in a geologic sense) a fracture surface upon which there has been slidingfissure – a fracture with walls that have separated and opened significantlyfracture front – the line separating the rock that has been fractured from the rock that has notfracture tip – the point at which the fracture trace terminates on the surfacefracture trace – the line representing the intersection of the fracture plane with the surfaceGriffith cracks – preexisting microfractures and flaws in the rockjoint – a natural fracture in the formation in which there is no measureable shear displacementKIC – critical stress intensity factor, aka fracture toughness – the stress intensity at which tensile fracture propagation may occurlithostatic pressure – the weight of the overlying column of rocklongitudinal splitting – fracture mechanism resulting from compression along an axis that creates fractures parallel to the load axispore fluid pressure – the pressure exerted by the fluid within the rock poresshear fracture – fractures across which shear displacement has occurredvein – a fracture filled with minerals precipitated out of an aqueous solutionwing cracks'' – tensile fractures created as a result of propagating shear fractures | Fracture (geology) | Wikipedia | 490 | 6985160 | https://en.wikipedia.org/wiki/Fracture%20%28geology%29 | Physical sciences | Structural geology | Earth science |
A secondary color is a color made by mixing two primary colors of a given color model in even proportions. Combining two secondary colors in the same manner produces a tertiary color. Secondary colors are special in traditional color theory, but have no special meaning in color science.
Overview
Primary color
In traditional color theory, it is believed that all colors can be mixed from 3 universal primary - or pure - colors, which were originally believed to be red, yellow and blue pigments (representing the RYB color model). However, modern color science does not recognize universal primary colors and only defines primary colors for a given color model or color space. RGB and CMYK color models are popular color models in modern color science, but are only chosen as efficient primaries, in that their combination leads to a large gamut. However, any three primaries can produce a viable color gamut. The RYB model continues to be used and taught as a color model for practical color mixing in the visual arts.
Secondary color
A secondary color is an even mixture of two primary colors. For a given color model, secondary colors have no special meaning, but are useful when comparing additive and subtractive color models.
Intermediate color
An intermediate color is any mixture of a secondary and a primary color. They are often visualized as even mixtures, but intermediate colors can arise from any mixture proportion. Therefore any color that is not a secondary or primary color is an intermediate color.
Tertiary color
Tertiary color has two common, conflicting definitions, depending on context.
In traditional color theory, which applies mostly to practical painting, a tertiary color is an even mixture between two secondary colors, i.e. a mixture of three primaries in 1:2:1 proportion. This definition is used by color theorists, such as Moses Harris and Josef Albers. The result is approximately a less saturated form of the dominant primary color of the mixture. Under this definition, a color model has 3 tertiary colors.
More recently, an alternative definition has emerged that is more applicable to digital media, where a tertiary color is an intermediate color resulting from an even mixture of a primary and a secondary color, i.e. a mixture of the primaries in 3:1:0 proportion. The result yields a maximum saturation for a given hue. Under this definition, a color model has 6 tertiary colors. | Secondary color | Wikipedia | 469 | 979990 | https://en.wikipedia.org/wiki/Secondary%20color | Physical sciences | Basics | Physics |
Quaternary color
A quaternary color is a seldom-used descriptor that is the conceptual extension of a tertiary color. Quaternary colors have no special use or status in color theory or color science.
Under the traditional definition, a quaternary color is the even mixture of two tertiary colors, as demonstrated by Charles Hayter. These quaternary colors have contributions from all three primaries in 3-3-2 proportions, so are very desaturated (even mixtures of three primaries gives a neutral color: zero saturation). Under this definition, a color model has 3 quaternary colors.
Under the modern definition, a quaternary color is the even mixture of a tertiary color with either a secondary or primary color. Quaternary colors are sometimes given a maximum saturation for their hue. Under this definition, a color model has 12 quaternary colors.
RGB and CMYK
The RGB color model is an additive mixing model, used to estimate the mixing of colored light, with primary colors red, green, and blue. The secondary colors are yellow, cyan and magenta as demonstrated here:
The CMY color model is an analogous subtractive mixing color model, used to estimate the mixing of colored pigments, with primary colors cyan, magenta, and yellow, equivalent to the secondary colors of the RGB color model. The secondary colors of the CMY model are blue, red and green, equivalent to the primary colors of the RGB model, as demonstrated here:
Under the modern definition, the 6 tertiary colors are conceptually equivalent between the color models, and can be described by the even combinations of a primary and a secondary color:
A color model is a conceptual model and does not have specifically defined primary colors. A color space based on the RGB color model, most commonly sRGB, has defined primaries and can be used to visualize the color mixing and yield approximate tertiary colors. Also note that the color terms applied to tertiary and quaternary colors are not well-defined.
RYB color model
RYB is a subtractive mixing color model, used to estimate the mixing of pigments (e.g. paint) in traditional color theory, with primary colors red, yellow, and blue. The secondary colors are green, purple, and orange as demonstrated here: | Secondary color | Wikipedia | 475 | 979990 | https://en.wikipedia.org/wiki/Secondary%20color | Physical sciences | Basics | Physics |
Under the modern definition (as even combinations of a primary and a secondary color), tertiary colors are typically named by combining the names of the adjacent primary and secondary color. However, these tertiary colors have also been ascribed with common names: amber/marigold (yellow-orange), vermilion/cinnabar (red-orange), magenta (red-purple), violet (blue-purple), teal/aqua (blue-green), and chartreuse/lime green (yellow-green). The 6 tertiary colors are given:
Approximate colors and color names are given for the tertiary and quaternary colors. However, the names for the twelve quaternary colors are quite variable, and defined here only as an approximation.
Under the traditional definition, there are three tertiary colors, approximately named russet (orange–purple), slate (purple–green), and citron (green–orange), with the corresponding three quaternary colors plum (russet–slate), sage (slate–citron), buff (citron–russet) (with olive sometimes used for either slate or citron). In every level of mixing, saturation of the resultant decreases and mixing two quaternary colors approaches gray.
The RYB color terminology outlined above and in the color samples shown below is ultimately derived from the 1835 book Chromatography, an analysis of the RYB color wheel by George Field, a chemist who specialized in pigments and dyes. | Secondary color | Wikipedia | 307 | 979990 | https://en.wikipedia.org/wiki/Secondary%20color | Physical sciences | Basics | Physics |
The humphead wrasse (Cheilinus undulatus) is a large species of wrasse mainly found on coral reefs in the Indo-Pacific region. It is also known as the Māori wrasse, Napoleon wrasse, Napoleon fish, so mei 蘇眉 (Cantonese), mameng (Filipino), and merer in the Pohnpeian language of the Caroline Islands.
Description
The humphead wrasse is the largest extant member of the family Labridae. Males, typically larger than females, are capable of reaching up to 2 meters and weighing up to 180 kg, but the average length is a little less than 1 meter. Females rarely grow larger than one meter. This species can be easily identified by its large size, thick lips, two black lines behind its eyes, and the hump on the foreheads of larger adults. Its color can vary between dull blue-green to more vibrant shades of green and purplish-blue. Adults are usually observed living singly, but are also seen in male/female pairs and in small groups.
Habitat
The humphead wrasses can be found on the east coast of Africa around the mouth of the Red Sea, and in some areas of the Indian and Pacific Oceans. Juveniles are usually found in shallow, sandy ranges bordering coral reef waters, while adults are found mostly in offshore and deeper areas of coral reefs, typically in outer-reef slopes and channels, but also in lagoons.
Reproduction
The humphead wrasse is long-lived, but has a very slow breeding rate. Individuals become sexually mature at five to seven years, and are known to live for around 30 years. They are protogynous hermaphrodites, with some becoming male at about 9 years old. The factors controlling the timing of sex change are not yet known. At certain times of year, adults move to the down-current end of the reef and form local spawning aggregations (groups). They likely do not travel very far for their spawning aggregations.
The pelagic eggs and larvae ultimately settle on or near coral reef habitats. Eggs are 0.65 mm in diameter and spherical, with no pigment.
Ecology | Humphead wrasse | Wikipedia | 443 | 980126 | https://en.wikipedia.org/wiki/Humphead%20wrasse | Biology and health sciences | Acanthomorpha | Animals |
Very opportunistic predators, C. undulatus preys primarily on invertebrates such as mollusks (particularly gastropods, as well as pelecypods, echinoids, crustaceans, and annelids) other fish, and even the highly venomous Crown-of-thorns starfish. Because half of echinoids and most pelecypods hide under the sand, wrasses may rely on fish excavators like stingrays, or they themselves may excavate by ejecting water to displace sand and nosing around for prey. Like many other Red Sea wrasses, humphead wrasses often crack sea urchins (echinoids) by carrying them to a rock in their mouths and striking them against the rock with brisk, sideways head movements.
They sometimes engage in cooperative hunting with the roving coral grouper.
Adults are commonly found on steep coral reef slopes, channel slopes, and lagoon reefs in water deep.
The species actively selects branching hard and soft corals and seagrasses at settlement. Juveniles tend to prefer a more cryptic existence in areas of dense branching corals, bushy macroalgae, or seagrasses, while larger individuals and adults prefer limited home ranges in more open habitat on the edges of reefs, channels, and reef passes.
Conservation | Humphead wrasse | Wikipedia | 274 | 980126 | https://en.wikipedia.org/wiki/Humphead%20wrasse | Biology and health sciences | Acanthomorpha | Animals |
The humphead wrasse is listed as endangered on the IUCN Red list and in Appendix II of CITES. Its numbers have declined due to multiple threats, including:
Intensive, species-specific removal by the live reef food-fish trade throughout its core range in Southeast Asia
Destructive fishing techniques, including bombs and cyanide
Habitat loss and degradation
Local consumption, and its perception as a delicacy to locals and tourists
A developing export market for juveniles for the marine aquarium trade
Lack of coordinated, consistent national and regional management
Inadequate knowledge of the species
Illegal, unreported and unregulated fishing
Unsustainable and severe overfishing within the live reef food fish trade is the primary threat. Sabah, on Borneo Island, is a major source of humphead wrasses. The fishing industry is vital to this state because of its severe poverty. The export of humphead wrasses out of Sabah has led to a roughly 99% decline in the area's population. In an effort to protect it, export of the humphead wrasse out of Sabah has been banned; however, it has not prevented illegal, unreported and unregulated activities. Protection by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) is managed in this area by the federal Department of Fisheries Malaysia, , which issues permits to regulate fishing activity. Two pieces of legislation have also been implemented to protect the species: The Fisheries Act 1985 controls the transport of live fish and prohibits destructive fishing techniques; and the International Trade in Endangered Species Act 2008 supports Malaysia's adoption of CITES.
The humphead wrasse is considered an umbrella species, which means many other species are sympatric with it and have much smaller ranges—thus the conservation of the humphead wrasse's habitat would benefit these other species as well. Understanding the concept of an umbrella species can lead to a better understanding of endangered species protection.
The humphead wrasse has historically been fished commercially in northern Australia, but has been protected in Queensland since 2003 and in Western Australia since 1998.
In Guangdong Province, southern mainland China, permits are required for the sale of the species. Indonesia allows fishing only for research, mariculture and licensed artisanal fishing. The Maldives instituted an export ban in 1995; Papua New Guinea prohibits export of fish over ; and Niue has banned all fishing for this species. | Humphead wrasse | Wikipedia | 489 | 980126 | https://en.wikipedia.org/wiki/Humphead%20wrasse | Biology and health sciences | Acanthomorpha | Animals |
The U.S. National Marine Fisheries Service has classified the humphead wrasse as a species of concern—one about which it has concerns, but for which it has insufficient information to list under the Endangered Species Act.
In Taiwan it is a protected species with fines of between NT$300,000 and $1.5 million and jail sentences of between 6 months and 5 years under the Wildlife Conservation act for hunting or killing of the species having been added to the protection list in 2014.
Population conservation by genetics
In 1996, following a decade of rapid population decline, the humphead wrasse was placed on the IUCN Red List of endangered species. The wrasse's genomes must be analyzed to help keep the species alive.
Since so little was known about the wrasse's genetic relationships at a geographical scale, researchers utilized a test using microsatellite loci to facilitate population genetic studies. (DNA markers could not be used for testing, as the humphead wrasse lack such markers.) Of the 15 microsatellite loci used in the test, only four seemed to have different outcomes than the other 11. These loci were all prone to null alleles. However, with the presence of these null alleles, the results may have been slightly biased, or they may be related to a particularity of the C. undulatus, which are highly restricted to coral reef habitats.
Illegal, unregulated and unreported activities
The Philippines, Indonesia, and Sabah Malaysia are the three largest exporters of the humphead wrasse. It has one of the highest retail values in Asia, especially when caught alive, and it is considered a delicacy in places like Malaysia. Illegal, unregulated, and unreported activities have been identified as the major factor for the failure of conservation efforts. Although the Convention on International Trade in Endangered Species of Wild Fauna and Flora has banned its export, the fish are still smuggled across the Malaysia–Philippines border. | Humphead wrasse | Wikipedia | 409 | 980126 | https://en.wikipedia.org/wiki/Humphead%20wrasse | Biology and health sciences | Acanthomorpha | Animals |
Four main factors have allowed illegal, unregulated and unreported activities to persist:
Lack of capacity – A lack exists of formal procedures and personnel to monitor fishing activities and enforce fishing regulations
Lack of disincentives – Fishers do not have alternatives for the humphead wrasse, due to its value, and sanctions for illegal fishing are not harsh enough to discourage them
Weak accountability systems – Because a number of people are involved in the species's trade, it is difficult to trace its source; and importers and consumers cannot be held responsible for illegal exportation.
Absent domestic trade controls – Domestic catching, possession, and trade are not sufficiently restricted. Fishers may illegally source the fish or intend to illegally trade it, but cannot be prosecuted if they are in Malaysian waters with appropriate permits.
Most exports of the humphead wrasse in Malaysia occur in Sandakan, Papar, and Tawau, where the fish could recently be purchased for between US$45.30 and $69.43, with its retail price ranging from $60.38 to $120.36. | Humphead wrasse | Wikipedia | 224 | 980126 | https://en.wikipedia.org/wiki/Humphead%20wrasse | Biology and health sciences | Acanthomorpha | Animals |
Diospyros is a genus of over 700 species of deciduous and evergreen trees and shrubs. The majority are native to the tropics, with only a few species extending into temperate regions. Individual species valued for their hard, heavy, dark timber, are commonly known as ebony trees, while others are valued for their fruit and known as persimmon trees. Some are useful as ornamentals and many are of local ecological importance. Species of this genus are generally dioecious, with separate male and female plants.
Taxonomy and etymology
The generic name Diospyros comes from a Latin name for the Caucasian persimmon (D. lotus), derived from the Greek διόσπυρος : dióspyros, from diós () and pyrós (). The Greek name literally means "Zeus's wheat" but more generally intends "divine food" or "divine fruit".
The genus is a large one and the number of species has been estimated variously, depending on the date of the source. The Royal Botanic Gardens, Kew, list has over 1000 entries, including synonyms and items of low confidence. Over 700 species are marked as being assigned with high confidence.
The oldest fossils of the genus date to the Eocene, which indicate by that time Diospyros was widely distributed over the Northern Hemisphere.
Chemotaxonomy
The leaves of Diospyros blancoi have been shown to contain isoarborinol methyl ether (also called cylindrin) and fatty esters of α- and β-amyrin. Both isoarborinol methyl ether and the amyrin mixture demonstrated antimicrobial activity against Escherichia coli, Pseudomonas aeruginosa, Candida albicans, Staphylococcus aureus, and Trichophyton interdigitale. Anti-inflammatory and analgesic properties have also been shown for the isolated amyrin mixture.
Ecology
Diospyros species are important and conspicuous trees in many of their native ecosystems, such as lowland dry forests of the former Maui Nui in Hawaii, Caspian Hyrcanian mixed forests, Khathiar–Gir dry deciduous forests, Louisiade Archipelago rain forests, Madagascar lowland forests, Narmada Valley dry deciduous forests, New Caledonian sclerophytic vegetation, New Guinea mangroves or South Western Ghats montane rain forests. | Diospyros | Wikipedia | 490 | 980257 | https://en.wikipedia.org/wiki/Diospyros | Biology and health sciences | Ericales | null |
The green fruits are avoided by most herbivores, perhaps because they are rich in tannins. When ripe, they are eagerly eaten by many animals however, such as (in East Africa) the rare Aders' duiker (Cephalophus adersi). The foliage is used as food by the larvae of numerous Lepidoptera species:
Arctiidae:
Eupseudosoma aberrans
Eupseudosoma involutum (snowy eupseudosoma)
Hypercompe indecisa
Geometridae:
Gymnoscelis rufifasciata (double-striped pug) – recorded on persimmons
Limacodidae:
Monema flavescens
Lycaenidae:
Neopithecops zalmora (Quaker)
Nymphalidae:
Charaxes khasianus (Kihansi charaxes) – recorded on D. natalensis
Dophla evelina (redspot duke) – recorded on D. candolleana
Saturniidae:
Actias luna (Luna moth) – recorded on persimmons
Callosamia promethea (promethea silkmoth) – recorded on persimmons
Citheronia regalis (regal moth) – recorded on American persimmon (D. virginiana)
Tortricidae:
"Cnephasia" jactatana (black-lyre leafroller moth)
An economically significant plant pathogen infecting many Diospyros species – D. hispida, kaki persimmon (D. kaki), date-plum (D. lotus), Texas persimmon (D. texana), Coromandel ebony (D. melanoxylon) and probably others – is the sac fungus Pseudocercospora kaki, which causes a leaf spot disease.
Use by humans
The genus includes several plants of commercial importance, either for their edible fruit (persimmons) or for their timber (ebony). The latter are divided into two groups in trade: the pure black ebony (notably from D. ebenum, but also several other species), and the striped ebony or calamander wood (from D. celebica, D. mun and others). Most species in the genus produce little to none of this black ebony-type wood; their hard timber (e.g. of American persimmon, D. virginiana) may still be used on a more limited basis. | Diospyros | Wikipedia | 509 | 980257 | https://en.wikipedia.org/wiki/Diospyros | Biology and health sciences | Ericales | null |
Leaves of the Coromandel ebony (D. melanoxylon) are used to roll South Asian beedi cigarettes. Several species are used in herbalism, and D. leucomelas yields the versatile medical compound betulinic acid. Extracts from Diospyros plants have also been proposed as novel anti-viral treatment. Though bees do not play a key role as pollinators, in plantations Diospyros may be of some use as honey plants. D. mollis, locally known as mặc nưa, is used in Vietnam to dye the famous black lãnh Mỹ A silk of Tân Châu district.
The reverence of these trees in their native range is reflected by their use as floral emblems. In Indonesia, D. celebica (Makassar ebony, known locally as eboni) is the provincial tree of Central Sulawesi, while ajan kelicung (D. macrophylla) is that of West Nusa Tenggara. The emblem of the Japanese island of Ishigaki is the Yaeyama kokutan (D. ferrea). The Gold apple (D. decandra), called "Trái thị" in Vietnamese, is a tree in the Tấm Cám fable. It is also the provincial tree of Chanthaburi as well as Nakhon Pathom Provinces in Thailand, while the black-and-white ebony (D. malabarica) is that of Ang Thong Province. The name of the Thai district Amphoe Tha Tako, literally means "District of the Diospyros pier", the latter being a popular local gathering spot.
Selected species | Diospyros | Wikipedia | 336 | 980257 | https://en.wikipedia.org/wiki/Diospyros | Biology and health sciences | Ericales | null |
Diospyros abyssinica
Diospyros acuminata
Diospyros alatella
Diospyros andamanica
Diospyros apiculata
Diospyros areolata
Diospyros artanthifolia
Diospyros atrata
Diospyros attenuata
Diospyros australis – yellow persimmon, black plum, "grey plum"
Diospyros beccarioides
Diospyros borneensis
Diospyros britannoborneensis
Diospyros buxifolia
Diospyros cambodiana
Diospyros candolleana
Diospyros celebica – Makassar ebony
Diospyros chaetocarpa
Diospyros chamaethamnus – sand apple
Diospyros chloroxylon
Diospyros clementium
Diospyros confertiflora
Diospyros cordata
Diospyros coriacea
Diospyros crassiflora – Gaboon ebony, Gabon ebony, African ebony, West African ebony, Benin ebony
Diospyros crockerensis
Diospyros curranii
Diospyros daemona
Diospyros decandra – gold apple
Diospyros dichrophylla
Diospyros dictyoneura
Diospyros diepenhorstii
Diospyros discocalyx
Diospyros discolor – kamagong, mabolo, butter fruit, velvet-apple
Diospyros duclouxii
Diospyros ebenum – Ceylon ebony, India ebony, "ebony"
Diospyros elliptifolia
Diospyros eriantha
Diospyros eucalyptifolia
Diospyros euphlehia
Diospyros evena
Diospyros everettii
Diospyros fasciculosa
Diospyros ferox
Diospyros ferrea
Diospyros ferruginescens
Diospyros foxworthyi
Diospyros frutescens
Diospyros fusiformis
Diospyros geminata
Diospyros hallieri
Diospyros havilandii
Diospyros hebecarpa
Diospyros hillebrandii
Diospyros hirsuta
Diospyros humilis – Queensland ebony
Diospyros inconstans
Diospyros insignis
Diospyros insularis – Papua ebony | Diospyros | Wikipedia | 510 | 980257 | https://en.wikipedia.org/wiki/Diospyros | Biology and health sciences | Ericales | null |
Diospyros kaki – Japanese persimmon, kaki persimmon, Asian persimmon
Diospyros keningauensis
Diospyros korthalsiana
Diospyros kurzii – Andaman marblewood
Diospyros lanceifolia
Diospyros lateralis
Diospyros leucomelas
Diospyros longibracteata
Diospyros lotus – date-plum, Caucasian persimmon, lilac persimmon
Diospyros lunduensis
Diospyros lycioides – bushveld bluebush
subsp. guerkei
subsp. nitens
subsp. sericea
Diospyros mabacea – red-fruited ebony
Diospyros macrophylla
Diospyros maingayi
Diospyros major
Diospyros malabarica – black-and-white ebony, pale moon ebony, Malabar ebony, gaub tree
Diospyros maritima
Diospyros marmorata – marblewood ebony, "marblewood"
Diospyros melanoxylon – Coromandel ebony, East Indian ebony
var. tupru
Diospyros mespiliformis – jackalberry, "African ebony"
Diospyros mindanaensis
Diospyros montana
Diospyros mun – mun ebony
Diospyros muricata
Diospyros neurosepala
Diospyros nigra – black sapote, chocolate pudding fruit, "black persimmon"
Diospyros oligantha
Diospyros oocarpa
Diospyros oppositifolia
Diospyros ovalifolia
Diospyros parabuxifolia
Diospyros pendula
Diospyros penibukanensis
Diospyros pentamera – myrtle ebony, grey persimmon, black myrtle, grey plum
Diospyros perfida
Diospyros pilosanthera
Diospyros piscicapa
Diospyros plectosepala
Diospyros puncticulosa
Diospyros pyrrhocarpa
Diospyros quaesita
Diospyros racemosa
Diospyros revaughanii
Diospyros rhombifolia
Diospyros ridleyi
Diospyros rigida
Diospyros rufa
Diospyros sandwicensis
Diospyros seychellarum
Diospyros siamang | Diospyros | Wikipedia | 506 | 980257 | https://en.wikipedia.org/wiki/Diospyros | Biology and health sciences | Ericales | null |
Diospyros simaloerensis
Diospyros singaporensis
Diospyros squamifolia
Diospyros squarrosa – rigid star-berry
Diospyros styraciformis
Diospyros subrhomboidea
Diospyros subtruncata
Diospyros sulcata
Diospyros sumatrana
Diospyros tessellaria – Mauritius ebony
Diospyros texana – Texas persimmon, Mexican persimmon, "black persimmon"
Diospyros thwaitesii
Diospyros tuberculata
Diospyros ulo
Diospyros venosa
var. olivacea
Diospyros virginiana – American persimmon, eastern persimmon, common persimmon, possumwood, "simmon", "sugar-plum"
Diospyros walkeri
Diospyros wallichii
Diospyros whyteana – Cape ebony | Diospyros | Wikipedia | 202 | 980257 | https://en.wikipedia.org/wiki/Diospyros | Biology and health sciences | Ericales | null |
Espalier ( or ) is the horticultural and ancient agricultural practice of controlling woody plant growth for the production of fruit, by pruning and tying branches to a frame. Plants are frequently shaped in formal patterns, flat against a structure such as a wall, fence, or trellis, and also plants which have been shaped in this way.
Espaliers, trained into flat two-dimensional forms, are used not only for decorative purposes, but also for gardens in which space is limited. In a temperate climate, espaliers may be trained next to a wall that can reflect more sunlight and retain heat overnight or oriented so that they absorb maximum sunlight by training them parallel to the equator. These two strategies allow the season to be extended so that fruit has more time to mature.
A restricted form of training consists of a central stem and a number of paired horizontal branches all trained in the same plane. The most important advantage is that of being able to increase the growth of a branch by training it vertically. Later, one can decrease growth while increasing fruit production by training it horizontally.
History
The word is French, coming from the Italian , meaning "something to rest the shoulder () against." During the 17th century, the word initially referred only to the actual trellis or frame on which such a plant was trained to grow, but over time it has come to be used to describe both the practice and the plants themselves.
Espalier as a technique seems to have started with the ancient Romans. In the Middle Ages the Europeans refined it into an art. The practice was popularly used in Europe to produce fruit inside the walls of a typical castle courtyard without interfering with the open space and to decorate solid walls by planting flattened trees near them. Vineyards have used the technique in the training of grapes for hundreds or perhaps even thousands of years.
Belgian fence
A Belgian fence is created by cutting back an unbranched, slender tree to between above the ground. The topmost three buds are allowed to form; one in the middle is trained vertically while two others are trained into a V shape. Any other buds are rubbed away. Removing the vertical stem completes the individual V-shaped espalier. By placing many similarly trained trees in a line two feet apart with their branches trained to the same plane, a Belgian fence is created. | Espalier | Wikipedia | 466 | 980345 | https://en.wikipedia.org/wiki/Espalier | Technology | Horticulture | null |
The Belgian fence is an intermediary form that can then be used to train onward to many other forms of espalier, including: Step-over, where the branches are lowered down to the horizontal in autumn while still flexible enough and tied to a trellis; Fan, where the branches are lowered and cut back then trained further; Horizontal T, where the branches are trained to horizontal as with step-over but the vertical stem is trained up to another level and cut usually in spring of the second year, where another V shape is created and the resulting branches finally being lowered to another wire in autumn of the second year. Multiple levels of horizontal branching can be trained in this way.
Species choices
Certain types of trees adapt better to espalier than others, but almost any woody plant can be trained to grow along a flat plane by removing growth outside that plane.
Horizontal T training of an apple or pear tree is a good example of the ideal species for espalier. In the spring, the tree is pruned to the lowest wire perhaps above the ground. During the summer, buds lengthen into branches; one trained vertically to the next wire while others are trained along the wires. Unnecessary buds are removed by rubbing them away with a thumb. In autumn, the side branches are lowered and tied to the wires completing the level. The following year another level is created.
Examples of species for espalier include: | Espalier | Wikipedia | 286 | 980345 | https://en.wikipedia.org/wiki/Espalier | Technology | Horticulture | null |
Trees:
Acer palmatum Japanese Maple
Cercis canadensis Redbud
Citrus spp. Lemon, Orange, Tangerine, etc.
Coccoloba uvifera Sea grape
Eriobotrya japonica Loquat
Euonymus alata Winged Euonymus
Ficus carica Fig
Forsythia intermedia Forsythia
Ilex spp. Hollies, esp. Ilex cornuta 'Burford Burford holly
Lagerstroemia indica Crape myrtle
Magnolia grandiflora Southern magnolia
Magnolia stellata Star Magnolia
Malus spp. Apple, Crabapple, etc.
Olea europia Olive
Prunus spp. Peach, Nectarine, Plum, Almond, etc.
Pyrus spp. Pear
Taxus sp. YewShrubs:Camellia japonica and C. sasanqua Camellia
Carissa grandiflora Natal plum
Chaenomeles lagenaria Chinese flowering quince
Cotoneaster sp. Cotoneaster
Gardenia jasminoides Gardenia
Juniperus spp. Juniper, esp. Juniperus × pfitzeriana''' Pfitzer juniperLigustrum japonicum PrivetOsmanthus fragrans Sweet OlivePhotinia glabra Redtip photiniaPhotinia serrulata Chinese PhotiniaPodocarpus spp. PodocarpusPyracantha spp. Firethorn, esp. Pyracantha coccinea Pyracantha coccinea
Stewartia Koreana Korean Stewartia
Viburnum sp. ViburnumWoody vines:'''Allamanda cathartica AllamandaFicus pumila Creeping figJasminum nudiflorum Winter JasminePyrostegia venusta Flame vineTrachelospermum jasminoides'' Confederate jasmine
Designs
Espalier design often uses traditional formal patterns developed over hundreds of years, but can also employ more modern informal designs. A stunted or deformed plant, or one that already has interesting or unique characteristics, might be just right for an informal espalier. | Espalier | Wikipedia | 427 | 980345 | https://en.wikipedia.org/wiki/Espalier | Technology | Horticulture | null |
Common formal patterns include the following styles.
V-shaped: Tree is cut to a low wire from the ground; two buds lengthen into branches which are attached to canes that keep them straight, and the canes are attached to another wire that maintains a V shape. The V shape is the first step in producing many other formal patterns.
Belgian fence: More than one V-shaped espaliers are planted two feet apart, so their branches cross, and are tied to a trellis.
Stepover: A Horizontal espalier with only one set of branches tied to a wire around above the ground. Start with a V shape until desired branch length is attained, but lower branches to the bottom wire by autumn of the first year. Takes only one year to produce the design from a well-rooted unbranched tree (it may take somewhat longer for it to start producing fruit).
Horizontal T, also referred to as a horizontal cordon: Branches are trained horizontally along evenly spaced wires. Start with a V shape where a third bud is trained straight up to another wire. Train other two branches to stepover. In spring of second year prune the vertical stem to the second wire and again train to a V shape, etc. It takes one year per each level.
Palmette or fan: Branches grow in a radiating pattern created when the branches of a V-shaped espalier are cut back and lowered slightly. Multiple buds are coaxed to form branches that are tied to a trellis in a radiating pattern.
Baldassari palmette: A palmette design created around 1950, used primarily for training peaches.
Cordon: Consists of a main stem with short fruiting spurs tied to a fence or a wire trellis. Probably the simplest and quickest espalier is the single vertical or angled cordon. The weakness of the vertical cordon is that it is difficult to rein in the vigor of the tree. An angled cordon reduces the vigor of its growth and increases fruit production.
Verrier candelabra is a type of vertical cordon with multiple upright stems that usually starts from a V shape.
Drapeau marchand: A cordon trained at an angle with the branches on its upper side trained to a right angle from the main stem.
U double and other U-shaped espalier is just another way of referring to a double vertical cordon.
Plant selection, installation, and maintenance | Espalier | Wikipedia | 491 | 980345 | https://en.wikipedia.org/wiki/Espalier | Technology | Horticulture | null |
Espalier plants on solid walls are usually installed from the base of that wall, to allow space below ground for roots to grow in all directions as well as space above ground for good air circulation and pest control. Supports for wire guides, which are generally necessary to train an espalier into a design, are installed first, directly into a wall constructed of suitable material. Masonry walls are ideal for placing U-bolts, eye bolts, or eye screws, anchored with either plastic plugs or expandable lead shields, directly into the mortar joints. Wooden walls may be better fitted with galvanized nipples, using turnbuckles for adjustment of the wire tautness.
Suitable, established and healthy plants, three to four feet tall and perhaps in three-gallon containers, are available from most nurseries. Some may even have trellises already installed. These plants could also be good candidates for espalier treatment if their form is similar to the intended design, as they frequently have already been pruned into a flattened overall plant shape. All that is required for such specimens is transplanting. Unpruned plants benefit from being allowed to become well established following transplant, before pruning them gradually into their flattened profile and training them as designed. Any major pruning needed is generally accomplished either while the plant is dormant or, for flowering plants, during the proper season for pruning that species. Bending and training of the limbs that will remain in the design is done during the progression of the summer season, when they are most flexible.
Related tree shaping practices
Bonsai: A small tree shaped to mimic the form of a full grown tree
Grafting: A horticultural technique of joining two or more plants together
Pleaching: Way of creating a hedge with plants for stock control
Topiary: The clipping of foliage of perennial plants into clearly defined shapes
Tree Shaping: Creating with living trees structures and art | Espalier | Wikipedia | 384 | 980345 | https://en.wikipedia.org/wiki/Espalier | Technology | Horticulture | null |
The white rhinoceros, white rhino or square-lipped rhinoceros (Ceratotherium simum) is the largest extant species of rhinoceros. It has a wide mouth used for grazing and is the most social of all rhino species. The white rhinoceros consists of two subspecies: the southern white rhinoceros, with an estimated 16,803
wild-living animals, and the much rarer northern white rhinoceros. The northern subspecies has very few remaining individuals, with only two confirmed left in 2018 (two females: Fatu, 24 and Najin, 29, both in captivity at Ol Pejeta). Sudan, the world's last known male northern white rhinoceros, died in Kenya on 19 March 2018 at age 45.
Naming
A popular albeit widely discredited theory of the origins of the name "white rhinoceros" is a mistranslation from Dutch to English. The English word "white" is said to have been derived by mistranslation of the Dutch word "wijd", which means "wide" in English. The word "wide" refers to the width of the rhinoceros' mouth. So early English-speaking settlers in South Africa misinterpreted the "wijd" for "white" and the rhino with the wide mouth ended up being called the white rhino and the other one, with the narrow pointed mouth, was called the black rhinoceros. Ironically, Dutch (and Afrikaans) later used a calque of the English word, and now also call it a white rhino. This suggests the origin of the word was before codification by Dutch writers. A review of Dutch and Afrikaans literature about the rhinoceros has failed to produce any evidence that the word wijd was ever used to describe the rhino outside of oral use.
An alternative name for the white rhinoceros, more accurate but rarely used, is the square-lipped rhinoceros. The white rhinoceros' generic name, Ceratotherium, given by the zoologist John Edward Gray in 1868, is derived from the Greek terms keras (κέρας) "horn" and thērion (θηρίον) "beast". Simum, is derived from the Greek term simos (σιμός), meaning "flat nosed".
Taxonomy and evolution | White rhinoceros | Wikipedia | 489 | 980916 | https://en.wikipedia.org/wiki/White%20rhinoceros | Biology and health sciences | Perissodactyla | Animals |
The white rhinoceros of today was said to be likely descended from Ceratotherium praecox, which lived around 7 million years ago. Remains of this white rhino have been found at Langebaanweg near Cape Town. A review of fossil rhinos in Africa by Denis Geraads has suggested, however, that the species from Langebaanweg is of the genus Ceratotherium, but not Ceratotherium praecox, as the type specimen of Ceratotherium praecox should, in fact, be Diceros praecox, given that it shows closer affinities with the black rhinoceros Diceros bicornis. It has been suggested that the modern white rhino's skull, which is longer than that of Ceratotherium praecox, evolved in order to facilitate consumption of shorter grasses that resulted from the long-term trend to drier conditions in Africa. However, if Ceratotherium praecox is in fact Diceros praecox, then the shorter skull could indicate a browsing species. Teeth of fossils assigned to Ceratotherium found at Makapansgat in South Africa were analysed for carbon isotopes, and the researchers concluded that these animals consumed more than 30% browse in their diet, suggesting that these are not the fossils of the extant Ceratotherium simum, which only eats grass. It is suggested that the real lineage of the white rhino should be: Ceratotherium neumayri → Ceratotherium mauritanicum → C. simum, with the Langebaanweg rhinos being Ceratotherium sp. (as yet unnamed), and with black rhinos being descended from C. neumayri via Diceros praecox. | White rhinoceros | Wikipedia | 386 | 980916 | https://en.wikipedia.org/wiki/White%20rhinoceros | Biology and health sciences | Perissodactyla | Animals |
Recently, an alternative scenario has been proposed under which the earliest African Ceratotherium is considered to be Ceratotherium efficax (now synonymous with C. mauritanicum), known from the Late Pliocene of Ethiopia and the Early Pleistocene of Tanzania. This species is proposed to have been diversified into the Middle Pleistocene species C. mauritanicum in northern Africa, C. germanoafricanum in East Africa, and the extant C. simum. The first two of these are extinct; however, C. germanoafricanum is very similar to C. simum and has often been considered a fossil and ancestral subspecies to the latter. The study also doubts the ancestry of C. neumayri from the Miocene of southern Europe to the African species.
The ancestor of both the black and the white rhino was likely a mixed feeder, with the two lineages then specializing in browsing and grazing, respectively. The oldest definitive record of the white rhinoceros is during the mid-Early Pleistocene at Olduvai Gorge in Tanzania, around 1.8 Ma.
Southern white rhinoceros
As of 2021, there were an estimated 15,940 southern white rhinos in the wild, making them by far the most abundant subspecies of rhino in the world. The number of southern white rhinos outnumbers all other rhino subspecies combined. South Africa is the stronghold for this subspecies, with 12,968 individuals recorded in 2021. There are smaller reintroduced populations within the historical range of the species in Namibia, Botswana, Zimbabwe, Uganda and Eswatini, while a small population survives in Mozambique. Populations have also been introduced outside of the former range of the species to Kenya and Zambia.
Northern white rhinoceros
The northern white rhinoceros or northern square-lipped rhinoceros (Ceratotherium simum cottoni) is considered critically endangered and possibly extinct in the wild. Formerly found in several countries in East and Central Africa south of the Sahara, this subspecies is a grazer in grasslands and savanna woodlands. | White rhinoceros | Wikipedia | 421 | 980916 | https://en.wikipedia.org/wiki/White%20rhinoceros | Biology and health sciences | Perissodactyla | Animals |
Initially, six northern white rhinoceros lived in the Dvůr Králové Zoo in the Czech Republic. Four of the six rhinos (which were also the only reproductive animals of this subspecies) were transported to Ol Pejeta Conservancy in Kenya, where scientists hoped they would successfully breed and save this subspecies from extinction. One of the two remaining in the Czech Republic died in late May 2011. Both of the last two bulls capable of natural mating died in 2014 (one in Kenya on 18 October and one in San Diego on 15 December). In 2015, the Kenyan government placed the last remaining bull of the subspecies at Ol Pejeta under 24-hour armed guard to deter poachers, but he was put down on 19 March 2018 due to multiple health problems caused by old age, leaving just two cows alive which reside at the Ol Pejeta complex. Staff hope to inseminate the remaining cows with the last bull's semen, although the semen is not preferable due to the age of the rhino.
Following the phylogenetic species concept, recent research has led to the hypothesis that the northern white rhinoceros is a different species, rather than a subspecies of white rhinoceros as was previously thought, in which case the correct scientific name for the former should be Ceratotherium cottoni. Distinct morphological and genetic differences suggest the two proposed species have been separated for at least a million years. However, the results of the research were not universally accepted by other scientists.
Description
The white rhinoceros is the largest of the five living species of rhinoceros. By mean body mass, the white rhinoceros falls behind only the three extant species of elephant as the largest land animal and terrestrial mammal alive today. It weighs slightly more on average than a hippopotamus despite a considerable mass overlap between these two species. It has a massive body and large head, a short neck and broad chest. | White rhinoceros | Wikipedia | 394 | 980916 | https://en.wikipedia.org/wiki/White%20rhinoceros | Biology and health sciences | Perissodactyla | Animals |
The head and body length is in bulls and in cows, with the tail adding another , and the shoulder height is in the bull and in the cow. The bull, averaging about is heavier than the cow, at an average of about . The largest size the species can attain is not definitively known; specimens of up to are considered reliable, while larger sizes up to have been claimed but are not verified. On its snout it has two horn-like growths, one behind the other. These are made of solid keratin, in which they differ from the horns of bovids (cattle and their relatives), which are keratin with a bony core, and deer antlers, which are solid bone. The average weight of a horn is about 4.0 kilograms (8.8 pounds).
The front horn is larger and averages in length, reaching as much as but only in cows. The white rhinoceros also has a noticeable hump on the back of its neck. Each of the four stumpy feet has three toes. The color of the body ranges from yellowish-brown to slate grey. Its only hair is the ear fringes and tail bristles. White rhinos have a distinctive broad, straight mouth which is used for grazing. Its ears can move independently to pick up sounds, but it depends most of all on its sense of smell. The olfactory passages that are responsible for smelling are larger than their entire brain. The white rhinoceros has the widest set of nostrils of any land-based animal.
Genome
The genome size of the white rhinoceros is 2581.22 Mb. A diploid cell has 2 x 40 autosomals and 2 sex chromosomes (XX or XY). | White rhinoceros | Wikipedia | 352 | 980916 | https://en.wikipedia.org/wiki/White%20rhinoceros | Biology and health sciences | Perissodactyla | Animals |
Behavior and ecology
White rhinos are grazing herbivores. They are found in grassland and savannah habitat. Preferring the shortest grains, the white rhinoceros is one of the largest pure grazers. It drinks twice a day if water is available, but if conditions are dry it can live four or five days without water. It spends about half of the day eating, one-third resting, and the rest of the day doing various other things. Like all species of rhinoceros, white rhinos enjoy wallowing in mud holes to cool down. The white rhinoceros is thought to have changed the structure and ecology of the savanna's grasslands. Comparatively, based on studies of the African elephant, scientists believe the white rhino is a driving factor in its ecosystem. The destruction of the megaherbivore could have serious cascading effects on the ecosystem and harm other animals.
White rhinos produce sounds that include a panting contact call, grunts and snorts during courtship, squeals of distress, and deep bellows or growls when threatened. Threat displays (in bulls mostly) include wiping its horn on the ground and a head-low posture with ears back, combined with snarl threats and shrieking if attacked. The vocalizations of the two species differ between each other, and the panting contact calls between individual white rhinos in each species can vary as well. The differences in these calls aid the white rhinos in identifying each other and communicating over long distances. The white rhinoceros is quick and agile and can run .
White rhinos live in crashes or herds of up to 14 animals (usually mostly cows). Sub-adult bulls will congregate, often in association with an adult cow. Most adult bulls are solitary. Dominant bulls mark their territory with excrement and urine. The dung is laid in well defined piles. It may have 20 to 30 of these piles to alert passing white rhinos that it is his territory. Another way of marking their territory is wiping their horns on bushes or the ground and scraping with their feet before urine spraying. They do this around ten times an hour while patrolling territory. The same ritual as urine marking except without spraying is also commonly used. The territorial bull will scrape-mark every 30 m (100 ft) or so around his territory boundary. Subordinate bulls do not mark territory. The most serious fights break out over mating rights with a cow. Cow territory overlaps extensively, and they do not defend it.
Reproduction | White rhinoceros | Wikipedia | 500 | 980916 | https://en.wikipedia.org/wiki/White%20rhinoceros | Biology and health sciences | Perissodactyla | Animals |
Cows reach sexual maturity at 6–7 years of age while bulls reach sexual maturity between 10 and 12 years of age. Courtship is often a difficult affair. The bull stays beyond the point where the cow acts aggressively and will give out a call when approaching her. The bull chases and or blocks the way of the cow while squealing or wailing loudly if the cow tries to leave his territory. When ready to mate, the cow curls her tail and gets into a stiff stance during the half-hour copulation. Breeding pairs stay together between 5–20 days before they part their separate ways. The gestation period of a white rhino is 16 months. A single calf is born and usually weighs . Calves are unsteady for their first two to three days of life. When threatened, the baby will run in front of the mother, which is very protective of her calf and will fight for it vigorously. Weaning starts at two months, but the calf may continue suckling for over 12 months. The birth interval for the white rhino is between two and three years. Before giving birth, the mother will chase off her current calf. White rhinos can live to be up to 40–50 years old.
Due to their size, adult white rhinos have no natural predators (other than humans), and even young rhinos are rarely attacked or preyed on due to the mother's presence and their tough skin. One exceptional, successful attack was perpetrated by a lion pride on a sick bull white rhinoceros, which weighed , and occurred in Mala Mala Game Reserve, South Africa.
Distribution
The southern white rhino lives in Southern Africa. About 98.5% of white rhinos live in just five countries (South Africa, Namibia, Zimbabwe, Kenya, and Uganda). Almost at the edge of extinction in the early 20th century, the southern subspecies have made a tremendous comeback. In 2001, it was estimated that there were 11,670 white rhinos in the wild, with a further 777 in captivity worldwide, making it the most common rhino in the world. By the end of 2007, wild-living southern white rhinos had increased to an estimated 17,480 animals (IUCN 2008). | White rhinoceros | Wikipedia | 448 | 980916 | https://en.wikipedia.org/wiki/White%20rhinoceros | Biology and health sciences | Perissodactyla | Animals |
The northern white rhino (Ceratotherium simum cottoni) formerly ranged over parts of northwestern Uganda, southern Chad, southwestern Sudan, the eastern part of Central African Republic, and northeastern Democratic Republic of the Congo (DRC). The last surviving population of wild northern white rhinos are or were in Garamba National Park, Democratic Republic of the Congo (DRC) but in August 2005, ground and aerial surveys conducted under the direction of African Parks Foundation and the African Rhino Specialist Group (ARSG) only found four animals: a solitary adult male and a group of one adult male and two adult females. In June 2008, it was reported that the species may have gone extinct in the wild.
Like the black rhino, the white rhino is under threat from habitat loss and poaching, most recently by Janjaweed. Although there are no measurable health benefits, the horn is sought after for traditional medicine and jewelry.
Poaching
Historically, the major factor in the decline of white rhinos was uncontrolled hunting in the colonial era, but now poaching for their horn is the primary threat. The white rhino is particularly vulnerable to hunting because it is a large and relatively unaggressive animal with very poor eyesight and generally living in herds.
Despite the lack of scientific evidence, the rhino horn is highly prized in traditional Asian medicine, where it is ground into a fine powder or manufactured into tablets to be used as a treatment for a variety of illnesses such as nosebleeds, strokes, convulsions, and fevers. Due to this demand, several highly organized and very profitable international poaching syndicates came into being and would carry out their poaching missions with advanced technologies ranging from night vision scopes, silenced weapons, darting equipment, and even helicopters. The ongoing conflict in the Democratic Republic of Congo and incursions by poachers, primarily coming from Sudan, have further disrupted efforts to protect the few remaining northern rhinos. | White rhinoceros | Wikipedia | 404 | 980916 | https://en.wikipedia.org/wiki/White%20rhinoceros | Biology and health sciences | Perissodactyla | Animals |
In 2013, poaching rates for white rhinos nearly doubled from the previous year. As a result, the white rhino has now received Near Threatened status as its total population tops out at 20,000 members. Poaching of the animal has gone virtually unchecked in most of Africa, and the non-violent nature of the rhinoceros makes it susceptible to poaching. Mozambique, one of the four main countries in which the white rhino lives, is used by poachers as a passageway to South Africa, which holds a fairly large number of white rhinos. Here, rhinos are regularly killed and their horns are smuggled out of the country. As of 2014, Mozambique labels white rhino poaching as a misdemeanor. The white rhino population in South Africa's Kruger National Park fell by 60% between 2013 and 2021, to an estimated 3,529 individuals.
In March 2017, poachers broke into the Thoiry Zoo, which is located in France. A southern white rhinoceros named Vince was found shot dead in his enclosure; the poachers had removed one of his horns and had attempted to remove his second horn. This is believed to be the first time that a rhinoceros had been killed in a European zoo.
Even with increased anti-poaching efforts in many African countries, many poachers are still willing to risk death or prison time because of the tremendous amount of money that they stand to make. Rhino horn can fetch tens of thousands of dollars per kilogram on the black market in Asia, and, depending on the exact price, can be worth more than its weight in gold. Poachers are also starting to use social media sites for obtaining information on the location of rhino in popular tourist attractions (such as Kruger National Park) by searching for geotagged photographs posted online by unsuspecting tourists. By using GPS coordinates of rhinos in recent photographs, poachers can more easily find and kill their targets.
Modern conservation tactics | White rhinoceros | Wikipedia | 410 | 980916 | https://en.wikipedia.org/wiki/White%20rhinoceros | Biology and health sciences | Perissodactyla | Animals |
The northern white rhino is critically endangered to the point that only two of these rhinos are known to remain in the world, both in captivity. Several conservation tactics have been taken to prevent this subspecies from disappearing from the planet. Perhaps the most notable type of conservation effort for these rhinos is having moved them from Dvur Kralove Zoo in the Czech Republic to Kenya's Ol Pejeta Conservancy on 20 December 2009, where they have been under constant watch every day, and have been given favorable climate and diet, to which they have adapted well, to boost their chances of reproducing.
To save the northern white rhino from extinction, Ol Pejeta Conservancy announced that it would introduce a fertile southern white rhino from Lewa Wildlife Conservancy in February 2014. They placed the male rhino in an enclosure with both female northern white rhinos in hopes to cross-breed the subspecies. Having the male rhino with two female rhinos was expected to increase competition for the female rhinos and, in theory, should result in more mating experiences. Ol Pejeta Conservancy did not announce any news of rhino mating.
On 22 August 2019, using (ICSI), eggs from Fatu and Najin "were successfully inseminated" using the seminal fluid from Saut and Suni. The male Sudan's sperm was harvested before his death and is still in Kenya. On 11 September 2019, it was announced that "two embryos" were generated and will be kept in a frozen state, until placed in a surrogate female. On 15 January 2020, it was announced that "another embryo" was created using the same techniques; all three embryos are "from Fatu".
In captivity
Most white rhinos in zoos are southern white rhinos; in 2021, it was estimated that there were over 1,000 southern white rhinos in captivity worldwide.
Wild-caught southern whites will readily breed in captivity given appropriate amounts of space and food, as well as the presence of other female rhinos of breeding age. However, for reasons that are not currently understood, the rate of reproduction is extremely low among captive-born southern white females. | White rhinoceros | Wikipedia | 447 | 980916 | https://en.wikipedia.org/wiki/White%20rhinoceros | Biology and health sciences | Perissodactyla | Animals |
The San Diego Zoo Safari Park in San Diego, California, United States, had two northern white rhinos, one of which was wild-caught. On 22 November 2015, a 41-year-old female named Nola (born in 1974), which had been on loan from the Dvůr Králové Zoo in Dvůr Králové, Czech Republic) since 1989, was euthanized after experiencing a downturn in health. On 14 December 2014, a 44-year-old male named Angalifu died of old age at the San Diego Zoo. The other four captive northern white rhinos were loaned to Ol Pejeta Conservancy in Kenya, and only two remain alive. Females Najin and Fatu are still living, while males Suni and Sudan died in 2014 and 2018, respectively. The northern white rhinos had been transferred to Ol Pejeta Conservancy from the Dvůr Králové Zoo in 2009 in an attempt to protect the taxa in their natural habitat. The only two northern white rhinos left are maintained under 24-hour armed guard in Kenya. | White rhinoceros | Wikipedia | 228 | 980916 | https://en.wikipedia.org/wiki/White%20rhinoceros | Biology and health sciences | Perissodactyla | Animals |
Oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust, composed of troctolite, gabbro and ultramafic cumulates. The crust overlies the rigid uppermost layer of the mantle. The crust and the rigid upper mantle layer together constitute oceanic lithosphere.
Oceanic crust is primarily composed of mafic rocks, or sima, which is rich in iron and magnesium. It is thinner than continental crust, or sial, generally less than 10 kilometers thick; however, it is denser, having a mean density of about 3.0 grams per cubic centimeter as opposed to continental crust which has a density of about 2.7 grams per cubic centimeter.
The crust uppermost is the result of the cooling of magma derived from mantle material below the plate. The magma is injected into the spreading center, which consists mainly of a partly solidified crystal mush derived from earlier injections, forming magma lenses that are the source of the sheeted dikes that feed the overlying pillow lavas. As the lavas cool they are, in most instances, modified chemically by seawater. These eruptions occur mostly at mid-ocean ridges, but also at scattered hotspots, and also in rare but powerful occurrences known as flood basalt eruptions. But most magma crystallises at depth, within the lower oceanic crust. There, newly intruded magma can mix and react with pre-existing crystal mush and rocks.
Composition | Oceanic crust | Wikipedia | 326 | 981252 | https://en.wikipedia.org/wiki/Oceanic%20crust | Physical sciences | Tectonics | Earth science |
Although a complete section of oceanic crust has not yet been drilled, geologists have several pieces of evidence that help them understand the ocean floor. Estimations of composition are based on analyses of ophiolites (sections of oceanic crust that are thrust onto and preserved on the continents), comparisons of the seismic structure of the oceanic crust with laboratory determinations of seismic velocities in known rock types, and samples recovered from the ocean floor by submersibles, dredging (especially from ridge crests and fracture zones) and drilling. Oceanic crust is significantly simpler than continental crust and generally can be divided in three layers. According to mineral physics experiments, at lower mantle pressures, oceanic crust becomes denser than the surrounding mantle.
Layer 1 is on an average 0.4 km thick. It consists of unconsolidated or semiconsolidated sediments, usually thin or even not present near the mid-ocean ridges but thickens farther away from the ridge. Near the continental margins sediment is terrigenous, meaning derived from the land, unlike deep sea sediments which are made of tiny shells of marine organisms, usually calcareous and siliceous, or it can be made of volcanic ash and terrigenous sediments transported by turbidity currents.
Layer 2 could be divided into two parts: layer 2A – 0.5 km thick uppermost volcanic layer of glassy to finely crystalline basalt usually in the form of pillow basalt, and layer 2B – 1.5 km thick layer composed of diabase dikes.
Layer 3 is formed by slow cooling of magma beneath the surface and consists of coarse grained gabbro and cumulate ultramafic rocks. It constitutes over two-thirds of oceanic crust volume with almost 5 km thickness.
Geochemistry
The most voluminous volcanic rocks of the ocean floor are the mid-oceanic ridge basalts, which are derived from low-potassium tholeiitic magmas. These rocks have low concentrations of large ion lithophile elements (LILE), light rare earth elements (LREE), volatile elements and other highly incompatible elements. There can be found basalts enriched with incompatible elements, but they are rare and associated with mid-ocean ridge hot spots such as surroundings of Galapagos Islands, the Azores and Iceland. | Oceanic crust | Wikipedia | 465 | 981252 | https://en.wikipedia.org/wiki/Oceanic%20crust | Physical sciences | Tectonics | Earth science |
Prior to the Neoproterozoic Era 1000 Ma ago the world's oceanic crust was more mafic than present-days'. The more mafic nature of the crust meant that higher amounts of water molecules (OH) could be stored the altered parts of the crust. At subduction zones this mafic crust was prone to metamorphose into greenschist instead of blueschist at ordinary blueschist facies.
Life cycle
Oceanic crust is continuously being created at mid-ocean ridges. As continental plates diverge at these ridges, magma rises into the upper mantle and crust. As the continental plates move away from the ridge, the newly formed rocks cool and start to erode with sediment gradually building up on top of them. The youngest oceanic rocks are at the oceanic ridges, and they get progressively older away from the ridges.
As the mantle rises it cools and melts, as the pressure decreases and it crosses the solidus. The amount of melt produced depends only on the temperature of the mantle as it rises. Hence most oceanic crust is the same thickness (7±1 km). Very slow spreading ridges (<1 cm·yr−1 half-rate) produce thinner crust (4–5 km thick) as the mantle has a chance to cool on upwelling and so it crosses the solidus and melts at lesser depth, thereby producing less melt and thinner crust. An example of this is the Gakkel Ridge under the Arctic Ocean. Thicker than average crust is found above plumes as the mantle is hotter and hence it crosses the solidus and melts at a greater depth, creating more melt and a thicker crust. An example of this is Iceland which has crust of thickness ~20 km. | Oceanic crust | Wikipedia | 355 | 981252 | https://en.wikipedia.org/wiki/Oceanic%20crust | Physical sciences | Tectonics | Earth science |
The age of the oceanic crust can be used to estimate the (thermal) thickness of the lithosphere, where young oceanic crust has not had enough time to cool the mantle beneath it, while older oceanic crust has thicker mantle lithosphere beneath it. The oceanic lithosphere subducts at what are known as convergent boundaries. These boundaries can exist between oceanic lithosphere on one plate and oceanic lithosphere on another, or between oceanic lithosphere on one plate and continental lithosphere on another. In the second situation, the oceanic lithosphere always subducts because the continental lithosphere is less dense. The subduction process consumes older oceanic lithosphere, so oceanic crust is seldom more than 200 million years old.
The process of super-continent formation and destruction via repeated cycles of creation and destruction of oceanic crust is known as the Wilson Cycle.
The oldest large-scale oceanic crust is in the west Pacific and north-west Atlantic — both are about up to 180-200 million years old. However, parts of the eastern Mediterranean Sea could be remnants of the much older Tethys Ocean, at about 270 and up to 340 million years old.
Magnetic anomalies
The oceanic crust displays a pattern of magnetic lines, parallel to the ocean ridges, frozen in the basalt. A symmetrical pattern of positive and negative magnetic lines emanates from the mid-ocean ridge. New rock is formed by magma at the mid-ocean ridges, and the ocean floor spreads out from this point. When the magma cools to form rock, its magnetic polarity is aligned with the then-current positions of the magnetic poles of the Earth. New magma then forces the older cooled magma away from the ridge. This process results in parallel sections of oceanic crust of alternating magnetic polarity. | Oceanic crust | Wikipedia | 374 | 981252 | https://en.wikipedia.org/wiki/Oceanic%20crust | Physical sciences | Tectonics | Earth science |
The Astoria–Megler Bridge is a steel cantilever through-truss bridge in the Pacific Northwest region of the United States that spans the lower Columbia River. It carries a section of U.S. Route 101 from Astoria, Oregon, to Point Ellice near Megler, Washington. Opened in 1966, it is the longest continuous truss bridge in North America.
The bridge is from the mouth of the river at the Pacific Ocean. The bridge is in length, and was the final segment of U.S. Route 101 to be completed between Olympia, Washington, and Los Angeles, California.
History
Ferry service between Astoria and the Washington side of the Columbia River began in 1926. The Oregon Department of Transportation purchased the ferry service in 1946. This ferry service did not operate during inclement weather and the half-hour travel time caused delays. In order to allow faster and more reliable crossings near the mouth of the river, a bridge was planned. The bridge was built jointly by the Oregon Department of Transportation and Washington State Department of Transportation. Following construction, the Oregon Department of Transportation became the lead agency responsible for maintenance and operating the structure.
Construction on the structure began on November 5, 1962, and the concrete piers were cast at Tongue Point, upriver. The steel structure was built in segments at Vancouver, Washington, upriver, then barged downstream where hydraulic jacks lifted them into place. The bridge opened to traffic on July 29, 1966, marking the completion of U.S. Route 101 and becoming the seventh major bridge built by Oregon in the 1950s–1960s; ferry service ended the night before. On August 27, 1966, Governors Mark Hatfield of Oregon and Dan Evans of Washington dedicated the bridge by cutting a ceremonial ribbon. The four-day ceremony was celebrated by 30,000 attendees who participated in parades, drives, and a marathon boat race from Portland to Astoria. The cost of the project was $24 million, equivalent to $ million in dollars, and was paid for by tolls that were removed on December 24, 1993, more than two years early.
Details | Astoria–Megler Bridge | Wikipedia | 417 | 981546 | https://en.wikipedia.org/wiki/Astoria%E2%80%93Megler%20Bridge | Technology | Bridges | null |
The bridge is in length and carries one lane of traffic in each direction. The cantilever-span section, which is closest to the Oregon side, is long, and its main (central) span measures . It was built to withstand wind gusts and river water speeds of . As of 2004, an average of 7,100 vehicles per day used the Astoria–Megler Bridge. Designed by William Adair Bugge construction of the cantilever truss bridge was completed by the DeLong Corporation, the American Bridge Company, and Pomeroy Gerwick.
The south end has the former toll plaza, at the end of a inclined ramp which forms a spiral bridge, going through a full 360-degree loop while gaining elevation over land to provide almost of clearance over the shipping channel (similarly to the Lincoln Tunnel Helix in Weehawken, New Jersey). The north end is an at-grade intersection with State Route 401. Since most of the northern portion of the bridge is over shallow, non-navigable water, it is low to the water.
Repainting the bridge was planned for May 2009 through 2011 and budgeted at $20 million, to be shared by the states of Oregon and Washington. A four-year planned paint stripping and repainting project was planned for March 2012 through December 2016.
In 2016, a colony of double-crested cormorants moved from nearby East Sand Island to the bridge, where they began nesting. Their presence caused issues with bridge inspections, as bird droppings and guano covered visual cracks, and nests obscured navigational lights used by ship traffic. The population of cormorants increased to 5,000 breeding pairs in 2020, prompting efforts by the Army Corps of Engineers to scare the birds from the bridge and relocate them back to East Sand Island.
Pedestrians
Normally, only motor vehicles and bicycles are allowed on the bridge—not pedestrians. There is no sidewalk and the shoulders are too narrow for pedestrians adjacent to traffic. However, one day a year—usually in October—the bridge is host to the Great Columbia Crossing. Participants are taken by shuttle to the Washington side, from where they run or walk to the Oregon side on a route across the bridge. Motor traffic is allowed to use only one lane (of two lanes) and is advised to expect delays during the two-hour event. For the first time, during the 2018 event, the Oregon Department of Transportation announced that the bridge would be closed to motor traffic. | Astoria–Megler Bridge | Wikipedia | 498 | 981546 | https://en.wikipedia.org/wiki/Astoria%E2%80%93Megler%20Bridge | Technology | Bridges | null |
Popular culture
The bridge itself is featured prominently in the movies Short Circuit, Kindergarten Cop, Free Willy 2: The Adventure Home, The Goonies, and Sometimes I Think About Dying. It stands in for the doomed fictional Madison Bridge in Irwin Allen's 1979 made-for-TV disaster movie The Night the Bridge Fell Down. Songwriter Sufjan Stevens most likely references the bridge in his song "Should Have Known Better" off his 2015 album Carrie & Lowell as a metaphor for dealing with his grief from the death of his mother.
Images | Astoria–Megler Bridge | Wikipedia | 107 | 981546 | https://en.wikipedia.org/wiki/Astoria%E2%80%93Megler%20Bridge | Technology | Bridges | null |
Ankylosaurus is a genus of armored dinosaur. Its fossils have been found in geological formations dating to the very end of the Cretaceous Period, about 68–66 million years ago, in western North America, making it among the last of the non-avian dinosaurs. It was named by Barnum Brown in 1908; it is monotypic, containing only A. magniventris. The generic name means "fused" or "bent lizard", and the specific name means "great belly". A handful of specimens have been excavated to date, but a complete skeleton has not been discovered. Though other members of Ankylosauria are represented by more extensive fossil material, Ankylosaurus is often considered the archetypal member of its group, despite having some unusual features.
Possibly the largest known ankylosaurid, Ankylosaurus is estimated to have been between long and to have weighed between . It was quadrupedal, with a broad, robust body. It had a wide, low skull, with two horns pointing backward from the back of the head, and two horns below these that pointed backward and down. Unlike other ankylosaurs, its nostrils faced sideways rather than towards the front. The front part of the jaws was covered in a beak, with rows of small, leaf-shaped teeth farther behind it. It was covered in armor plates, or osteoderms, with bony half-rings covering the neck, and had a large club on the end of its tail. Bones in the skull and other parts of the body were fused, increasing their strength, and this feature is the source of the genus name. | Ankylosaurus | Wikipedia | 337 | 983374 | https://en.wikipedia.org/wiki/Ankylosaurus | Biology and health sciences | Ornitischians | Animals |
Ankylosaurus is a member of the family Ankylosauridae, and its closest relatives appear to be Anodontosaurus and Euoplocephalus. Ankylosaurus is thought to have been a slow-moving animal, able to make quick movements when necessary. Its broad muzzle indicates it was a non-selective browser. Sinuses and nasal chambers in the snout may have been for heat and water balance or may have played a role in vocalization. The tail club is thought to have been used in defense against predators or in intraspecific combat. Specimens of Ankylosaurus have been found in the Hell Creek, Lance, Scollard, Frenchman, and Ferris formations, but it appears to have been rare in its environment. Although it lived alongside a nodosaurid ankylosaur, their ranges and ecological niches do not appear to have overlapped, and Ankylosaurus may have inhabited upland areas. Ankylosaurus also lived alongside dinosaurs such as Tyrannosaurus, Triceratops, and Edmontosaurus.
History of discovery
In 1906, an American Museum of Natural History expedition led by American paleontologist Barnum Brown discovered the type specimen of Ankylosaurus magniventris (AMNH 5895) in the Hell Creek Formation, near Gilbert Creek, Montana. The specimen (found by collector Peter Kaisen) consisted of the upper part of a skull, two teeth, part of the shoulder girdle, cervical, dorsal, and caudal vertebrae, ribs, and more than thirty osteoderms (armor plates). Brown scientifically described the animal in 1908; the generic name is derived from the Greek words ('bent' or 'crooked'), referring to the medical term ankylosis, the stiffness produced by the fusion of bones in the skull and body, and ('lizard'). The name can be translated as "fused lizard", "stiff lizard", or "curved lizard". The type species name, magniventris, is derived from the ('great') and ('belly'), referring to the great width of the animal's body. | Ankylosaurus | Wikipedia | 446 | 983374 | https://en.wikipedia.org/wiki/Ankylosaurus | Biology and health sciences | Ornitischians | Animals |
The skeletal reconstruction accompanying the 1908 description restored the missing parts in a fashion similar to Stegosaurus, and Brown likened the result to the extinct armored mammal Glyptodon. In contrast to modern depictions, Brown's stegosaur-like reconstruction showed robust forelimbs, a strongly arched back, a pelvis with prongs projecting forwards from the ilium and pubis, as well as a short, drooping tail without a tail club, which was unknown at the time. Brown also reconstructed the armor plates in parallel rows running down the back; this arrangement was purely hypothetical. Brown's reconstruction became highly influential, and restorations of the animal based on his diagram were published as late as the 1980s. In a 1908 review of Brown's Ankylosaurus description, the American paleontologist Samuel Wendell Williston criticized the skeletal reconstruction as being based on too few remains, and claimed that Ankylosaurus was merely a synonym of the genus Stegopelta, which Williston had named in 1905. Williston also stated that a skeletal reconstruction of the related Polacanthus by Hungarian paleontologist Franz Nopcsa was a better example of how ankylosaurs would have appeared in life. The claim of synonymy was not accepted by other researchers, and the two genera are now considered distinct.
Brown had collected 77 osteoderms while excavating a Tyrannosaurus specimen in the Lance Formation of Wyoming in 1900. He mentioned these osteoderms (specimen AMNH 5866) in his description of Ankylosaurus but thought they belonged to the Tyrannosaurus instead. Paleontologist Henry Fairfield Osborn also expressed this view when he described the Tyrannosaurus specimen as the now synonymous genus Dynamosaurus in 1905. More recent examination has shown them to be similar to those of Ankylosaurus; it seems that Brown had compared them with some Euoplocephalus osteoderms, which had been erroneously cataloged as belonging to Ankylosaurus at the AMNH. | Ankylosaurus | Wikipedia | 414 | 983374 | https://en.wikipedia.org/wiki/Ankylosaurus | Biology and health sciences | Ornitischians | Animals |
In 1910, another AMNH expedition led by Brown discovered an Ankylosaurus specimen (AMNH 5214) in the Scollard Formation by the Red Deer River in Alberta, Canada. This specimen included a complete skull, mandibles, the first and only tail club known of this genus, as well as ribs, vertebrae, limb bones, and armor. In 1947 the American fossil collectors Charles M. Sternberg and T. Potter Chamney collected a skull and mandible (specimen CMN 8880, formerly NMC 8880), north of where the 1910 specimen was found. This is the largest-known Ankylosaurus skull, but it is damaged in places. A section of caudal vertebrae (specimen CCM V03) was discovered in the 1960s in the Powder River drainage, Montana, part of the Hell Creek Formation. In addition to these five incomplete specimens, many other isolated osteoderms and teeth have been found.
In 1990, American paleontologist Walter P. Coombs pointed out that the teeth of two skulls assigned to A. magniventris differed from those of the holotype specimen in some details, and though he expressed a "considerate temptation" to name a new species of Ankylosaurus for these, he refrained from doing so, as the range of variation in the species was not completely documented. He also raised the possibility that the two teeth associated with the holotype specimen perhaps did not belong to it, as they were found in matrix within the nasal chambers. The American paleontologist Kenneth Carpenter accepted the teeth as belonging to A. magniventris in 2004, and that all the specimens belonged to the same species, noting that the teeth of other ankylosaurs are highly variable. | Ankylosaurus | Wikipedia | 364 | 983374 | https://en.wikipedia.org/wiki/Ankylosaurus | Biology and health sciences | Ornitischians | Animals |
Most of the known Ankylosaurus specimens were not scientifically described at length, though several paleontologists planned to do so until Carpenter redescribed the genus in 2004. In 2017 the Canadian paleontologists Victoria M. Arbour and Jordan Mallon redescribed the genus in light of newer ankylosaur discoveries, including elements of the holotype that had not been previously mentioned in the literature (such as parts of the skull and the cervical half-rings). They concluded that though Ankylosaurus is the best-known member of its group, it was bizarre in comparison to related ankylosaurs, and therefore not representative of the group. In spite of its familiarity, it is known from far fewer remains than its closest relatives.
Description
Ankylosaurus was the largest-known ankylosaurine dinosaur and possibly the largest ankylosaurid. In 2004 Carpenter estimated that the individual with the largest-known skull (specimen CMN 8880), which is long and wide, was about long and had a hip height of about . The smallest-known skull (specimen AMNH 5214) is long and wide, and Carpenter estimated that it measured about long and about tall at the hips. The English paleontologist Roger B. J. Benson and colleagues estimated the weight for AMNH 5214 at in 2014.
In 2017, based on comparisons with more complete ankylosaurines, Arbour and Mallon estimated a length of for CMN 8880, and for AMNH 5214. Though the latter is the smallest specimen of Ankylosaurus, its skull is still larger than those of any other ankylosaurins. A few other ankylosaurs reached about in length. Because the vertebrae of AMNH 5214 are not significantly larger than those of other ankylosaurines, Arbour and Mallon considered their upper range estimate of nearly for large Ankylosaurus too long, and suggested a length of instead. Arbour and Mallon estimated a weight of for AMNH 5214, and tentatively estimated the weight of CMN 8880 at .
Skull | Ankylosaurus | Wikipedia | 437 | 983374 | https://en.wikipedia.org/wiki/Ankylosaurus | Biology and health sciences | Ornitischians | Animals |
The three known Ankylosaurus skulls differ in various details; this is thought to be the result of taphonomy (changes happening during decay and fossilization of the remains) and individual variation. The skull was low and triangular in shape, and wider than it was long; the back of the skull was broad and low. The skull had a broad beak on the premaxillae. The orbits (eye sockets) were almost round to slightly oval and did not face directly sideways because the skull tapered towards the front. The braincase was short and robust, as in other ankylosaurines. Crests above the orbits merged into the upper squamosal horns (their shape has been described as "pyramidal"), which pointed backwards to the sides from the back of the skull. The crest and horn were probably separate elements originally, as seen in the related Pinacosaurus and Euoplocephalus. Below the upper horns, jugal horns were present, which pointed backward and down. The horns may have originally been osteoderms that fused to the skull. The scale-like cranial ornamentation on the surfaces of ankylosaurs skulls is called "", and were the result of remodeling of the skull itself. This obliterated the sutures between skull elements, which is common for adult ankylosaurs. The caputegulum pattern of the skull was variable between specimens, though some details are shared. The caputegulae are named according to their position on the skull, and those of Ankylosaurus include a relatively large, hexagonal (or diamond-shaped) nasal caputegulum at the front of the snout between the nostrils, which had a loreal caputegulum on each side, an anterior and posterior supraorbital caputegulum above each orbit, and a ridge of nuchal caputegulae at the back of the skull. | Ankylosaurus | Wikipedia | 400 | 983374 | https://en.wikipedia.org/wiki/Ankylosaurus | Biology and health sciences | Ornitischians | Animals |
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