9 B Min
Pleistocene megafauna is the set of large animals that lived on Earth during the Pleistocene epoch and became extinct during the Quaternary extinction event. Megafauna are any animals with an adult body weight of over 45 kilograms (99 lb).[citation needed]
https://en.wikipedia.org/wiki/Pleistocene_megafauna
Past: Most Populous Countries in 1950
| # | Country | Population (1950) | World Share | 2020 Rank |
|---|---|---|---|---|
| 1 | China | 554,419,273 | 21.9 % | (1) |
| 2 | India | 376,325,200 | 14.8 % | (2) |
| 3 | United States | 158,804,395 | 6.3 % | (3) |
| 4 | Russia | 102,798,657 | 4.1 % | (9) |
| 5 | Japan | 82,802,084 | 3.3 % | (11) |
| 6 | Germany | 69,966,243 | 2.8 % | (19) |
| 7 | Indonesia | 69,543,316 | 2.7 % | (4) |
| 8 | Brazil | 53,974,729 | 2.1 % | (6) |
| 9 | United Kingdom | 50,616,014 | 2 % | (21) |
| 10 | Italy | 46,598,601 | 1.8 % | (23) |
| 11 | France | 41,833,882 | 1.6 % | (22) |
| 12 | Bangladesh | 37,894,681 | 1.5 % | (8) |
| 13 | Nigeria | 37,859,748 | 1.5 % | (7) |
| 14 | Pakistan | 37,542,376 | 1.5 % | (5) |
| 15 | Ukraine | 37,297,648 | 1.5 % | (35) |
| 16 | Spain | 28,069,735 | 1.1 % | (30) |
| 17 | Mexico | 27,944,669 | 1.1 % | (10) |
| 18 | Poland | 24,824,018 | 1 % | (38) |
| 19 | Vietnam | 24,809,902 | 1 % | (15) |
| 20 | Turkey | 21,408,399 | 0.8 % | (17) |
Future: Most Populous Countries in 2050
| # | Country | Population (2050) | World Share | 2020 Rank |
|---|---|---|---|---|
| 1 | India | 1,639,176,033 | 16.8 % | (2) |
| 2 | China | 1,402,405,170 | 14.4 % | (1) |
| 3 | Nigeria | 401,315,000 | 4.1 % | (7) |
| 4 | United States | 379,419,102 | 3.9 % | (3) |
| 5 | Pakistan | 338,013,196 | 3.5 % | (5) |
| 6 | Indonesia | 330,904,664 | 3.4 % | (4) |
| 7 | Brazil | 228,980,400 | 2.4 % | (6) |
| 8 | Ethiopia | 205,410,675 | 2.1 % | (12) |
| 9 | DR Congo | 194,488,658 | 2 % | (16) |
| 10 | Bangladesh | 192,567,778 | 2 % | (8) |
| 11 | Egypt | 159,956,808 | 1.6 % | (14) |
| 12 | Mexico | 155,150,818 | 1.6 % | (10) |
| 13 | Philippines | 144,488,158 | 1.5 % | (13) |
| 14 | Russia | 135,824,481 | 1.4 % | (9) |
| 15 | Tanzania | 129,386,839 | 1.3 % | (24) |
| 16 | Vietnam | 109,605,011 | 1.1 % | (15) |
| 17 | Japan | 105,804,027 | 1.1 % | (11) |
| 18 | Iran | 103,098,075 | 1.1 % | (18) |
| 19 | Turkey | 97,139,570 | 1 % | (17) |
| 20 | Kenya | 91,575,089 | 0.9 % | (27) |
https://www.worldometers.info/world-population/
−13 — – −12 — – −11 — – −10 — – −9 — – −8 — – −7 — – −6 — – −5 — – −4 — – −3 — – −2 — – −1 — – 0 — |
| ||||||||||||||||||||||||||||||||||||||||
In the 18th century, the concept that the age of the Earth was millions, if not billions, of years began to appear. However, most scientists throughout the 19th century and into the first decades of the 20th century presumed that the universe itself was Steady State and eternal, possibly with stars coming and going but no changes occurring at the largest scale known at the time.
https://en.wikipedia.org/wiki/Age_of_the_universe
The Cambrian explosion or Cambrian radiation[1] was an event approximately 541 million years ago in the Cambrian period when practically all major animal phylastarted appearing in the fossil record.[2][3] It lasted for about 13[4][5][6] – 25[7][8] million years and resulted in the divergence of most modern metazoan phyla.[9] The event was accompanied by major diversifications in other groups of organisms as well.[a]
Before the Cambrian explosion,[b] most organisms were relatively simple, composed of individual cells, or small multicellular organisms, occasionally organized into colonies. As the rate of diversification subsequently accelerated, the variety of life became much more complex, and began to resemble that of today.[11] Almost all present-day animal phyla appeared during this period.[12][13]
Cambodian Explosion; Cambodian Radiation; Cambodian Period, etc.
Before the Cambrian explosion,[b] most organisms (Americans) were relatively simple, composed of individual cells, or small multicellular organisms, occasionally organized into colonies (North America Continent Groups). As the rate of diversification subsequently accelerated (by trafficking), the variety of life became much more complex, and began to resemble that of today.[11] Almost all present-day animal phyla appeared during this period.[12][13]
https://en.wikipedia.org/wiki/Cambrian_explosion
The Cryogenian ( /kraɪoʊˈdʒɛniən/, from Ancient Greek: κρύος, romanized: krýos, meaning "cold" and γένεσις, romanized: génesis, meaning "birth") is a geologic period that lasted from 720 to 635 million years ago.[6]It forms the second geologic period of the Neoproterozoic Era, preceded by the Tonian Period and followed by the Ediacaran.
The Sturtian and Marinoan glaciations occurred during the Cryogenian period,[7] which are the greatest ice ages known to have occurred on Earth. These events are the subject of much scientific controversy. The main debate contests whether these glaciations covered the entire planet (the so-called "Snowball Earth") or a band of open sea survived near the equator (termed "slushball Earth").
https://en.wikipedia.org/wiki/Cryogenian
The Snowball Earth hypothesis proposes that during one or more of Earth's icehouse climates, Earth's surface became entirely or nearly entirely frozen, sometime earlier than 650 Mya (million years ago) during the Cryogenianperiod. Proponents of the hypothesis argue that it best explains sedimentarydeposits generally regarded as of glacial origin at tropical palaeolatitudes and other enigmatic features in the geological record. Opponents of the hypothesis contest the implications of the geological evidence for global glaciation and the geophysical feasibility of an ice- or slush-covered ocean[3][4] and emphasize the difficulty of escaping an all-frozen condition. A number of unanswered questions remain, including whether Earth was a full snowball, or a "slushball" with a thin equatorial band of open (or seasonally open) water.
The snowball-Earth episodes are proposed to have occurred before the sudden radiation of multicellular bioforms known as the Cambrian explosion. The most recent snowball episode may have triggered the evolution of multicellularity. Another, much earlier and longer snowball episode, the Huronian glaciation, which would have occurred 2400 to 2100 Mya, may have been triggered by the first appearance of oxygen in the atmosphere, the "Great Oxidation Event".
https://en.wikipedia.org/wiki/Snowball_Earth
| Chronology | ||||||
|---|---|---|---|---|---|---|
| ||||||
| Proposed subdivisions | See text | |||||
The Paleoarchean (/ˌpeɪlioʊɑːrˈkiːən/), also spelled Palaeoarchaean(formerly known as early Archean), is a geologic era within the Archaean eon. It spans the period of time 3,600 to 3,200 million years ago—the era is defined chronometrically and is not referenced to a specific level of a rock section on Earth. The name derives from Greek "Palaios" ancient. The oldest ascertained life form of fossilized bacteria in microbial mats, 3,480 million years old, found in the Dresser Formation in Western Australia, is from this era.[2][3] The first supercontinent Vaalbara formed during this period.
During this era, a large asteroid, about 37 to 58 kilometres (23–36 mi) wide, collided with the Earth in the area of South Africa about 3.26 billion years ago, creating the features known as the Barberton greenstone belt.[4]
https://en.wikipedia.org/wiki/Paleoarchean
The Mesoarchean (/ˌmiːzoʊɑːrˈkiːən/, also spelled Mesoarchaean) is a geologicera within the Archean Eon, spanning 3,200 to 2,800 million years ago. The era is defined chronometrically and is not referenced to a specific level in a rock section on Earth. The Pongola glaciation occurred around 2,900 million years ago.[1] The first supercontinent Vaalbara broke up during this era about 2,800 million years ago.
Analysis of oxygen isotopes in Mesoarchean cherts led to an oceanic temperature estimate around 55-85 °C,[2] while other studies of weathering rates postulate average temperatures below 50 °C.[3] Dinitrogen content in the atmosphere is thought to have been fundamentally similar to today's, and the partial pressure of carbon dioxide was probably lower than 0.7 bar.[4]
https://en.wikipedia.org/wiki/Mesoarchean
The Neoarchean (/ˌniːoʊɑːrˈkiːən/; also spelled Neoarchaean) is a geologicera within the Archaean Eon.
The Neoarchean spans the period from 2,800 to 2,500 million years ago— the period being defined chronometrically and not referenced to a specific level in a rock section on Earth.
https://en.wikipedia.org/wiki/Neoarchean
https://en.wikipedia.org/wiki/Hadean
The Cenozoic (/ˌsiː.nəˈzoʊ.ɪk, -noʊ-, ˌsɛn.ə-, ˌsɛn.oʊ-/ see-nə-ZOH-ik, -noh-, SEN-ə-, SEN-oh-;[1][2] lit. 'new life') is Earth's current geological era, representing the last 66 million years of Earth's history. It is characterized by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configuration of continents. It is the latest of three geological eras since complex life evolved, preceded by the Mesozoic and Paleozoic. It started with the Cretaceous–Paleogene extinction event, when many species, including the non-avian dinosaurs, became extinct in an event attributed by most experts to the impact of a large asteroid or other celestial body, the Chicxulub impactor.
The Cenozoic is also known as the Age of Mammals because the terrestrial animals that dominated both hemispheres were mammals – the eutherians (placentals) in the northern hemisphere and the metatherians (marsupials, now mainly restricted to Australia) in the southern hemisphere. The extinction of many groups allowed mammals and birds to greatly diversify so that large mammals and birds dominated the Earth. The continents also moved into their current positions during this era.
The Earth's climate had begun a drying and cooling trend, culminating in the glaciations of the Pleistocene Epoch, and partially offset by the Paleocene-Eocene Thermal Maximum.
| Cenozoic | |
|---|---|
| 66.0 – 0 Ma | |
 |
https://en.wikipedia.org/wiki/Cenozoic
The Paleogene (/ˈpeɪl.i.əˌdʒiːn, -i.oʊ-, ˈpæ.li-, -li.oʊ-/ PAL-ee-ə-jeen, -ee-oh-, PAY-lee-, -lee-oh-; also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period 66 million years ago (Mya) to the beginning of the Neogene Period 23.03 Mya. It is the beginning of the Cenozoic Era of the present Phanerozoic Eon. The earlier term Tertiary Period was used to define the span of time now covered by the Paleogene and subsequent Neogene periods; despite no longer being recognised as a formal stratigraphic term, 'Tertiary' is still widely found in earth science literature and remains in informal use.[5] The Paleogene is most notable for being the time during which mammals diversified from relatively small, simple forms into a large group of diverse animals in the wake of the Cretaceous–Paleogene extinction event that ended the preceding Cretaceous Period.[6] The United States Geological Survey uses the abbreviation PE for the Paleogene,[7][8] but the more commonly used abbreviation is PG with PE being used for Paleocene, an epoch within the Paleogene.
https://en.wikipedia.org/wiki/Cenozoic
https://en.wikipedia.org/wiki/Paleogene
The Neogene ( /ˈniː.əˌdʒiːn, ˈniː.oʊ-/ NEE-ə-jeen, NEE-oh-)[6][7] (informally Upper Tertiary or Late Tertiary) is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period 23.03 million years ago (Mya) to the beginning of the present Quaternary Period 2.58 Mya. The Neogene is sub-divided into two epochs, the earlier Mioceneand the later Pliocene. Some geologists assert that the Neogene cannot be clearly delineated from the modern geological period, the Quaternary.[8]The term "Neogene" was coined in 1853 by the Austrian palaeontologist Moritz Hörnes (1815–1868).[9]
During this period, mammals and birds continued to evolve into modern forms, while other groups of life remained relatively unchanged. The first humans (Homo habilis) appeared in Africa near the end of the period.[10]Some continental movement took place, the most significant event being the connection of North and South America at the Isthmus of Panama, late in the Pliocene. This cut off the warm ocean currents from the Pacific to the Atlantic Ocean, leaving only the Gulf Stream to transfer heat to the Arctic Ocean. The global climate cooled considerably over the course of the Neogene, culminating in a series of continental glaciations in the Quaternary Period that follows.
https://en.wikipedia.org/wiki/Neogene
Quaternary ( /kwəˈtɜːrnəri, ˈkwɒt.ərˌnɛr.i/ kwə-TUR-nə-ree, KWOT-ər-nerr-ee) is the current and most recent of the three periods of the Cenozoic Erain the geologic time scale of the International Commission on Stratigraphy(ICS).[4] It follows the Neogene Period and spans from 2.588 ± 0.005 million years ago to the present.[4] The Quaternary Period is divided into two epochs: the Pleistocene (2.588 million years ago to 11.7 thousand years ago) and the Holocene (11.7 thousand years ago to today, although a third epoch, the Anthropocene, has been proposed but is not yet officially recognized by the ICS).[4] The informal term "Late Quaternary" refers to the past 0.5–1.0 million years.[5]
The Quaternary Period is typically defined by the cyclic growth and decay of continental ice sheets related to the Milankovitch cycles and the associated climate and environmental changes that they caused.[6][7]
−2.6 — – −2.4 — – −2.2 — – −2 — – −1.8 — – −1.6 — – −1.4 — – −1.2 — – −1 — – −0.8 — – −0.6 — – −0.4 — – −0.2 — – 0 — | Q u a t e r n a r y |
| ||
https://en.wikipedia.org/wiki/Quaternary
https://en.wikipedia.org/wiki/Quaternary
The Holocene ( /ˈhɒl.əˌsiːn, ˈhɒl.oʊ-, ˈhoʊ.lə-, ˈhoʊ.loʊ-/ HOL-ə-seen, HOL-oh-, HOH-lə-, HOH-loh-)[2][3] is the current geological epoch. It began approximately 11,650 cal years before present, after the last glacial period, which concluded with the Holocene glacial retreat.[4] The Holocene and the preceding Pleistocene[5] together form the Quaternary period. The Holocene has been identified with the current warm period, known as MIS 1. It is considered by some to be an interglacial period within the Pleistocene Epoch, called the Flandrian interglacial.[6]
The Holocene corresponds with the rapid proliferation, growth and impacts of the human species worldwide, including all of its written history, technological revolutions, development of major civilizations, and overall significant transition towards urban living in the present. The human impact on modern-era Earth and its ecosystems may be considered of global significance for the future evolution of living species, including approximately synchronous lithospheric evidence, or more recently hydrospheric and atmospheric evidence of the human impact. In July 2018, the International Union of Geological Sciences split the Holocene epoch into three distinct subsections, Greenlandian (11,700 years ago to 8,200 years ago), Northgrippian (8,200 years ago to 4,200 years ago) and Meghalayan (4,200 years ago to the present), as proposed by International Commission on Stratigraphy.[7]The boundary stratotype of the Meghalayan is a speleothem in Mawmluh cave in India,[8] and the global auxiliary stratotype is an ice core from Mount Logan in Canada.[9]
The Holocene can be subdivided into five time intervals, or chronozones, based on climatic fluctuations:[19]
- Preboreal (10 ka–9 ka BP),
- Boreal (9 ka–8 ka BP),
- Atlantic (8 ka–5 ka BP),
- Subboreal (5 ka–2.5 ka BP) and
- Subatlantic (2.5 ka BP–present).
- Note: "ka BP" means "kilo-annum Before Present", i.e. 1,000 years before 1950 (non-calibrated C14 dates)
https://en.wikipedia.org/wiki/Holocene
https://en.wikipedia.org/wiki/Paleogene
https://en.wikipedia.org/wiki/Cenozoic
https://en.wikipedia.org/wiki/Hadean
https://en.wikipedia.org/wiki/Age_of_the_universe
A chronozone or chron is a unit in chronostratigraphy, defined by events such as geomagnetic reversals (magnetozones), or based on the presence of specific fossils (biozone or biochronozone). According to the International Commission on Stratigraphy, the term "chronozone" refers to the rocks formed during a particular time period, while "chron" refers to that time period.[1]
Although non-hierarchical, chronozones have been recognized as useful markers or benchmarks of time in the rock record. Chronozones are non-hierarchical in that chronozones do not need to correspond across geographic or geologic boundaries, nor be equal in length. Although a former, early constraint required that a chronozone be defined as smaller than a geological stage. Another early use was hierarchical in that Harland et al. (1989) used "chronozone" for the slice of time smaller than a faunal stagedefined in biostratigraphy. [2] The ICS superseded these earlier usages in 1994.[3]
The key factor in designating an internationally acceptable chronozone is whether the overall fossil column is clear, unambiguous, and widespread. Some accepted chronozones contain others, and certain larger chronozones have been designated which span whole defined geological time units, both large and small. For example, the chronozone Pliocene is a subset of the chronozone Neogene, and the chronozone Pleistocene is a subset of the chronozone Quaternary.
| Segments of rock (strata) in chronostratigraphy | Time spans in geochronology | Notes to geochronological units |
|---|---|---|
| Eonothem | Eon | 4 total, half a billion years or more |
| Erathem | Era | 10 defined, several hundred million years |
| System | Period | 22 defined, tens to ~one hundred million years |
| Series | Epoch | 34 defined, tens of millions of years |
| Stage | Age | 99 defined, millions of years |
| Chronozone | Chron | subdivision of an age, not used by the ICS timescale |
https://en.wikipedia.org/wiki/Chronozone
The 8.2-ka event, an abrupt cold spell recorded as a negative excursion in the δ18O record lasting 400 years, is the most prominent climatic event occurring in the Holocene epoch, and may have marked a resurgence of ice cover. It has been suggested that this event was caused by the final drainage of Lake Agassiz, which had been confined by the glaciers, disrupting the thermohaline circulation of the Atlantic.[37] Subsequent research, however, suggested that the discharge was probably superimposed upon a longer episode of cooler climate lasting up to 600 years and observed that the extent of the area affected was unclear.[38]
https://en.wikipedia.org/wiki/Chronozone
Thermohaline circulation (THC) is a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes.[1][2] The adjective thermohalinederives from thermo- referring to temperature and -haline referring to salt content, factors which together determine the density of sea water. Wind-driven surface currents (such as the Gulf Stream) travel polewards from the equatorial Atlantic Ocean, cooling en route, and eventually sinking at high latitudes (forming North Atlantic Deep Water). This dense water then flows into the ocean basins. While the bulk of it upwells in the Southern Ocean, the oldest waters (with a transit time of about 1000 years)[3] upwell in the North Pacific.[4]Extensive mixing therefore takes place between the ocean basins, reducing differences between them and making the Earth's oceans a global system. The water in these circuits transport both energy (in the form of heat) and mass (dissolved solids and gases) around the globe. As such, the state of the circulation has a large impact on the climate of the Earth.
The thermohaline circulation is sometimes called the ocean conveyor belt, the great ocean conveyor, or the global conveyor belt. On occasion, it is used to refer to the meridional overturning circulation (often abbreviated as MOC). The term MOC is more accurate and well defined, as it is difficult to separate the part of the circulation which is driven by temperature and salinity alone as opposed to other factors such as the wind and tidal forces.[5] Moreover, temperature and salinity gradients can also lead to circulation effects that are not included in the MOC itself.
https://en.wikipedia.org/wiki/Thermohaline_circulation
The drilling site of the North Greenland Ice Core Project (NGRIP or NorthGRIP) is near the center of Greenland (75.1 N, 42.32 W, 2917 m, ice thickness 3085). Drilling began in 1999 and was completed at bedrock in 2003.[1] The cores are cylinders of ice 11 centimeters in diameter that were brought to the surface in 3.5-meter lengths. The NGRIP site was chosen to extract a long and undisturbed record stretching into the last glacial, and it succeeded. The site was chosen for a flat basal topography to avoid the flow distortions that render the bottom of the GRIP and GISP cores unreliable. Unusually, there is melting at the bottom of the NGRIP core - believed to be due to a high geothermal heat flux locally. This has the advantage that the bottom layers are less compressed by thinning than they would otherwise be: NGRIP annual layers at 105 kyr age are 1.1 cm thick, twice the GRIP thicknesses at equal age.
The NGRIP record helps to resolve a problem with the GRIP and GISP2 records - the unreliability of the Eemian Stage portion of the record. NGRIP covers 5 kyr of the Eemian, and shows that temperatures then were roughly as stable as the pre-industrial Holocenetemperatures were. This is confirmed by sediment cores, in particular MD95-2042.[2]
In 2003, NGRIP recovered what seem to be plant remnants nearly two miles below the surface, and they may be several million years old.[3]
"Several of the pieces look very much like blades of grass or pine needles," said University of Colorado at Boulder geological sciences Professor James White, an NGRIP principal investigator. "If confirmed, this will be the first organic material ever recovered from a deep ice-core drilling project," he said.
https://en.wikipedia.org/wiki/North_Greenland_Ice_Core_Project
6.114 Billion Year 2000 ago etc. J2000 occurrance NLAB appear planetearthy
Means per each couple expect six children, with at least digit(sigfigure)*value reserve children (underground, donated, sharing, etc.). three units reserve children. max 999 w approp scaling or excission by 10. Family estimate at six type four placeholder family size one region/etc..
Example. Norway six childs per couple, 114-1000 reserve childs min; max unk/und/np/etc. (zero vert zero mat infinity on matricing zeros with constant max out and no count of loss/death/etc. ever scale after). Max cap satisfied to sustain animal, human designed human, cloak, large family, unwanted cunts, misters, jewejs, germs, neanders, heathens, stolen child demand, slaves, covetry inspired acquisition (dop/bop sh), trafficker, clone, human being, cellular lifeform: J2000.
Many species of Pleistocene megafauna, like the woolly rhinoceros, became extinct around the same time period. Human huntingis often cited as one cause. Other theories for the cause of the extinctions are climate change associated with the receding Ice ageand the hyperdisease hypothesis (q.v. Quaternary extinction event).[63] One of the more widely accepted theories states that, although the woolly rhinoceros was specialized for cold weather, it was capable of surviving in warmer climates. This suggests that climate change was not the only factor contributing to the rhinoceros's extinction. Other cold-adapted species, such as reindeer, muskox and wisent, survived this period of climatic change and many others like it, supporting the 'overkill' hypothesis for the woolly rhino.
Radiocarbon dating indicates that populations survived as recently as 8,000 BC in western Siberia.[64] However, the accuracy of this date is uncertain, as several radiocarbon plateaus exist around this time. The extinction does not coincide with the end of the last ice age, but does coincide with a minor yet severe climatic reversal that lasted for about 1,000–1,250 years, the Younger Dryas (GS1—Greenland Stadial 1), characterized by glacial readvances and severe cooling globally, a brief interlude in the continuing warming subsequent to the termination of the last major ice age (GS2), thought to have been due to a shutdown of the thermohaline circulation in the ocean due to huge influxes of cold fresh water from the preceding sustained glacial melting during the warmer Interstadial (GI1—Greenland Interstadial 1: ca. 16,000–11,450 14C years B.P.).
https://en.wikipedia.org/wiki/Woolly_rhinoceros
Glaciovolcanism is volcanism and related phenomena associated with glacial ice. The ice commonly constrains the erupted material and melts to create meltwater. Considerable melting of glacial ice can create massive lahars and glacial outburst floods known as jökulhlaups.[1]
https://en.wikipedia.org/wiki/Glaciovolcanism
A jökulhlaup (Icelandic pronunciation: [ˈjœːkʏl̥ˌl̥œip] 
pronunciation (help·info)) (literally "glacial run") is a type of glacial outburst flood.[1] It is an Icelandicterm that has been adopted in glaciological terminology in many languages. It originally referred to the well-known subglacial outburst floods from Vatnajökull, Iceland, which are triggered by geothermal heating and occasionally by a volcanic subglacial eruption, but it is now used to describe any large and abrupt release of water from a subglacial or proglacial lake/reservoir.
Since jökulhlaups emerge from hydrostatically-sealed lakes with floating levels far above the threshold, their peak discharge can be much larger than that of a marginal or extra-marginal lake burst. The hydrograph of a jökulhlaup from Vatnajökull typically either climbs over a period of weeks with the largest flow near the end, or it climbs much faster during the course of some hours. These patterns are suggested to reflect channel melting, and sheet flow under the front, respectively.[2] Similar processes on a very large scale occurred during the deglaciation of North America and Europe after the last ice age (e.g., Lake Agassiz and the English Channel), and presumably at earlier times, although the geological record is not well preserved.
Subglacial meltwater generation is one key to the understanding of subglacial meltwater flow. Meltwater may be produced on the glacier surface (supraglacially), below the glacier (basally) or in both locations.[3][4] Ablation (surface melting) tends to result in surface pooling. Basal melting results from geothermal heat flux out of the earth, which varies with location, as well as from friction heating which results from the ice moving over the surface below it. Analyses by Piotrowski concluded that, based on basal meltwater production rates, the annual production of subglacial water from one typical northwestern Germany catchment was 642x106 m3 during the last Weichselian glaciation.[5]
Meltwater may flow either above the glacier (supraglacially), below the glacier (subglacially/basally) or as groundwater in an aquifer below the glacier as a result of the hydraulic transmissivity of the subsoil under the glacier. If the rate of production exceeds the rate of loss through the aquifer, then water will collect in surface or subglacial ponds or lakes.[5]
The signatures of supraglacial and basal water flow differ with the passage zone. Supraglacial flow is similar to stream flow in all surface environments—water flows from higher areas to lower areas under the influence of gravity. Basal flow under the glacier exhibits significant differences. In basal flow the water, either produced by melting at the base or drawn downward from the surface by gravity, collects at the base of the glacier in ponds and lakes in a pocket overlain by hundreds of metres of ice. If there is no surface drainage path, water from surface melting will flow downward and collect in crevices in the ice, while water from basal melting collects under the glacier; either source can form a subglacial lake. The hydraulic head of the water collected in a basal lake will increase as water drains through the ice until the pressure grows high enough either to force a path through the ice or to float the ice above it.[3][6]
Whilst jökulhlaups were originally associated with Vatnajökull, they have been reported in the literature over a broad range of locations including the present day Antarctic, and there is evidence that they also occurred in the Laurentian ice sheet[9][10][11][12] and the Scandinavian ice sheet during the Last Glacial Maximum.[13]
Iceland[edit]
- Mýrdalsjökull is subject to large jökulhlaups when the subglacial volcano Katla erupts, roughly every 40 to 80 years. The eruption in 1755 is estimated to have had a peak discharge of 200,000 to 400,000 m3/s.
- The Grímsvötn volcano frequently causes large jökulhlaups from Vatnajökull. The 1996 eruption caused a peak flow of 50,000 m3/s and lasted for several days.
- The Eyjafjallajökull volcano can cause jökulhlaups. The 2010 eruption caused a jökulhlaup with a peak flow of about 2,000 to 3,000 m3/s.[14][15]
https://en.wikipedia.org/wiki/Jökulhlaup
No comments:
Post a Comment