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Last Glacial Period

The Last Glacial Period (LGP), also known colloquially as the last ice age or simply ice age,[1] occurred from the end of the Eemian to the end of the Younger Dryas, encompassing the period c. 115,000 – c. 11,700 years ago. The LGP is part of a larger sequence of glacial and interglacial periods known as the Quaternary glaciation which started around 2,588,000 years ago and is ongoing.[2] The definition of the Quaternary as beginning 2.58 million years ago (Mya) is based on the formation of the Arctic ice cap. The Antarctic ice sheet began to form earlier, at about 34 Mya, in the mid-Cenozoic (Eocene–Oligocene extinction event). The term Late Cenozoic Ice Age is used to include this early phase.[3] The previous ice age, the Saalian glaciation, which ended about 128,000 years ago, was more severe than the Last Glacial Period in some areas such as Britain, but less severe in others.

Chronology of climatic events of importance for the last glacial period (about the last 120,000 years)

During this last glacial period, alternating episodes of glacier advance, and retreat occurred. Within the last glacial period, the Last Glacial Maximum was approximately 22,000 years ago. While the general pattern of global cooling and glacier advance was similar, local differences in the development of glacier advance and retreat make comparing the details from continent to continent difficult (see picture of ice core data below for differences). Around 12,800 years ago, the Younger Dryas, the most recent glacial epoch, began, a coda to the preceding 100,000-year glacial period. Its end about 11,550 years ago marked the beginning of the Holocene, the current geological epoch.

From the point of view of human archaeology, the LGP falls in the Paleolithic and early Mesolithic periods. When the glaciation event started, Homo sapiens was confined to lower latitudes and used tools comparable to those used by Neanderthals in western and central Eurasia and by Denisovans and Homo erectus in Asia. Archaeological and genetic data suggest that the source populations of Paleolithic humans survived the LGP in sparsely wooded areas, and dispersed through areas of high primary productivity, while avoiding dense forest cover.[4]

Artist's impression of the last glacial period at glacial maximum[5]

Origin and definition

The LGP is often colloquially referred to as the "last ice age", though the term ice age is not strictly defined, and on a longer geological perspective, the last few million years could be termed a single ice age given the continual presence of ice sheets near both poles. Glacials are somewhat better defined, as colder phases during which glaciers advance, separated by relatively warm interglacials. The end of the last glacial period, which was about 10,000 years ago, is often called the end of the ice age, although extensive year-round ice persists in Antarctica and Greenland. Over the past few million years, the glacial-interglacial cycles have been "paced" by periodic variations in the Earth's orbit via Milankovitch cycles.

The LGP has been intensively studied in North America, northern Eurasia, the Himalayas, and other formerly glaciated regions around the world. The glaciations that occurred during this glacial period covered many areas, mainly in the Northern Hemisphere and to a lesser extent in the Southern Hemisphere. They have different names, historically developed and depending on their geographic distributions: Fraser (in the Pacific Cordillera of North America), Pinedale (in the Central Rocky Mountains), Wisconsinan or Wisconsin (in central North America), Devensian (in the British Isles),[6] Midlandian (in Ireland), Würm (in the Alps), Mérida (in Venezuela), Weichselian or Vistulian (in Northern Europe and northern Central Europe), Valdai in Russia and Zyryanka in Siberia, Llanquihue in Chile, and Otira in New Zealand. The geochronological Late Pleistocene includes the late glacial (Weichselian) and the immediately preceding penultimate interglacial (Eemian) period.

Overview

 
Vegetation types at time of Last glacial maximum
 
Last glacial period, as seen in ice core data from Antarctica and Greenland

Northern Hemisphere

Canada was nearly completely covered by ice, as was the northern part of the United States, both blanketed by the huge Laurentide Ice Sheet. Alaska remained mostly ice free due to arid climate conditions. Local glaciations existed in the Rocky Mountains and the Cordilleran ice sheet and as ice fields and ice caps in the Sierra Nevada in northern California.[7] In northern Eurasia, the Scandinavian ice sheet once again reached the northern parts of the British Isles, Germany, Poland, and Russia, extending as far east as the Taymyr Peninsula in western Siberia.[8] The maximum extent of western Siberian glaciation was reached by about 18,000 to 17,000 BP, thus later than in Europe (22,000–18,000 BP)[9] Northeastern Siberia was not covered by a continental-scale ice sheet.[10] Instead, large, but restricted, icefield complexes covered mountain ranges within northeast Siberia, including the Kamchatka-Koryak Mountains.[11][12]

The Arctic Ocean between the huge ice sheets of America and Eurasia was not frozen throughout, but like today, probably was covered only by relatively shallow ice, subject to seasonal changes and riddled with icebergs calving from the surrounding ice sheets. According to the sediment composition retrieved from deep-sea cores, even times of seasonally open waters must have occurred.[13]

Outside the main ice sheets, widespread glaciation occurred on the highest mountains of the Alpide belt. In contrast to the earlier glacial stages, the Würm glaciation was composed of smaller ice caps and mostly confined to valley glaciers, sending glacial lobes into the Alpine foreland. Local ice fields or small ice sheets could be found capping the highest massifs of the Pyrenees, the Carpathian Mountains, the Balkan mountains, the Caucasus, and the mountains of Turkey and Iran.[14]

In the Himalayas and the Tibetan Plateau, there is evidence that glaciers advanced considerably, particularly between 47,000 and 27,000 BP,[15] but the exact ages,[16][17] as well as the formation of a single contiguous ice sheet on the Tibetan Plateau, is controversial.[18][19][20]

Other areas of the Northern Hemisphere did not bear extensive ice sheets, but local glaciers were widespread at high altitudes. Parts of Taiwan, for example, were repeatedly glaciated between 44,250 and 10,680 BP[21] as well as the Japanese Alps. In both areas, maximum glacier advance occurred between 60,000 and 30,000 BP.[22] To a still lesser extent, glaciers existed in Africa, for example in the High Atlas, the mountains of Morocco, the Mount Atakor massif in southern Algeria, and several mountains in Ethiopia. Just south of the equator, an ice cap of several hundred square kilometers was present on the east African mountains in the Kilimanjaro massif, Mount Kenya, and the Rwenzori Mountains, which still bear relic glaciers today.[23]

Southern Hemisphere

Glaciation of the Southern Hemisphere was less extensive. Ice sheets existed in the Andes (Patagonian Ice Sheet), where six glacier advances between 33,500 and 13,900 BP in the Chilean Andes have been reported.[24] Antarctica was entirely glaciated, much like today, but unlike today the ice sheet left no uncovered area. In mainland Australia only a very small area in the vicinity of Mount Kosciuszko was glaciated, whereas in Tasmania glaciation was more widespread.[25] An ice sheet formed in New Zealand, covering all of the Southern Alps, where at least three glacial advances can be distinguished.[26] Local ice caps existed in the highest mountains of the island of New Guinea, where temperatures were 5 to 6° C colder than at present.[27][28] The main areas of Papua New Guinea where glaciers developed during the LGP were the Central Cordillera, the Owen Stanley Range, and the Saruwaged Range. Mount Giluwe in the Central Cordillera had a "more or less continuous ice cap covering about 188 km2 and extending down to 3200-3500 m".[27] In Western New Guinea, remnants of these glaciers are still preserved atop Puncak Jaya and Ngga Pilimsit.[28]

Small glaciers developed in a few favorable places in Southern Africa during the last glacial period.[29][A][B] These small glaciers would have been located in the Lesotho Highlands and parts of the Drakensberg.[31][32] The development of glaciers was likely aided in part due to shade provided by adjacent cliffs.[32] Various moraines and former glacial niches have been identified in the eastern Lesotho Highlands a few kilometres west of the Great Escarpment, at altitudes greater than 3,000 m on south-facing slopes.[31] Studies suggest that the annual average temperature in the mountains of Southern Africa was about 6°C colder than at present, in line with temperature drops estimated for Tasmania and southern Patagonia during the same time. This resulted in an environment of relatively arid periglaciation without permafrost, but with deep seasonal freezing on south-facing slopes. Periglaciation in the eastern Drakensberg and Lesotho Highlands produced solifluction deposits and blockfields; including blockstreams and stone garlands.[29][30]

Deglaciation

 
Temperature rise marking the end of the most recent ice age, as derived from ice core data.

Scientists from the Center for Arctic Gas Hydrate, Environment and Climate at the University of Tromsø, published a study in June 2017[33] describing over a hundred ocean sediment craters, some 3,000 m wide and up to 300 m deep, formed by explosive eruptions of methane from destabilized methane hydrates, following ice-sheet retreat during the LGP, around 12,000 years ago. These areas around the Barents Sea still seep methane today. The study hypothesized that existing bulges containing methane reservoirs could eventually have the same fate.

Named local glaciations

Antarctica

During the last glacial period, Antarctica was blanketed by a massive ice sheet, much as it is today; however, the ice covered all land areas and extended into the ocean onto the middle and outer continental shelf.[34][35] Counterintuitively though, according to ice modeling done in 2002, ice over central East Antarctica was generally thinner than it is today.[36]

Europe

Devensian and Midlandian glaciation (Britain and Ireland)

British geologists refer to the LGP as the Devensian. Irish geologists, geographers, and archaeologists refer to the Midlandian glaciation, as its effects in Ireland are largely visible in the Irish Midlands. The name Devensian is derived from the Latin Dēvenses, people living by the Dee (Dēva in Latin), a river on the Welsh border near which deposits from the period are particularly well represented.[37]

The effects of this glaciation can be seen in many geological features of England, Wales, Scotland, and Northern Ireland. Its deposits have been found overlying material from the preceding Ipswichian stage and lying beneath those from the following Holocene, which is the current stage. This is sometimes called the Flandrian interglacial in Britain.

The latter part of the Devensian includes pollen zones I–IV, the Allerød oscillation and Bølling oscillation, and the Oldest Dryas, Older Dryas, and Younger Dryas cold periods.

Weichselian glaciation (Scandinavia and northern Europe)

 
Europe during the last glacial period

Alternative names include Weichsel glaciation or Vistulian glaciation (referring to the Polish River Vistula or its German name Weichsel). Evidence suggests that the ice sheets were at their maximum size for only a short period, between 25,000 and 13,000 BP. Eight interstadials have been recognized in the Weichselian, including the Oerel, Glinde, Moershoofd, Hengelo, and Denekamp; however, correlation with isotope stages is still in process.[38][39] During the glacial maximum in Scandinavia, only the western parts of Jutland were ice-free, and a large part of what is today the North Sea was dry land connecting Jutland with Britain (see Doggerland).

The Baltic Sea, with its unique brackish water, is a result of meltwater from the Weichsel glaciation combining with saltwater from the North Sea when the straits between Sweden and Denmark opened. Initially, when the ice began melting about 10,300 BP, seawater filled the isostatically depressed area, a temporary marine incursion that geologists dub the Yoldia Sea. Then, as postglacial isostatic rebound lifted the region about 9500 BP, the deepest basin of the Baltic became a freshwater lake, in palaeological contexts referred to as Ancylus Lake, which is identifiable in the freshwater fauna found in sediment cores. The lake was filled by glacial runoff, but as worldwide sea level continued rising, saltwater again breached the sill about 8000 BP, forming a marine Littorina Sea, which was followed by another freshwater phase before the present brackish marine system was established. "At its present state of development, the marine life of the Baltic Sea is less than about 4000 years old", Drs. Thulin and Andrushaitis remarked when reviewing these sequences in 2003.

Overlying ice had exerted pressure on the Earth's surface. As a result of melting ice, the land has continued to rise yearly in Scandinavia, mostly in northern Sweden and Finland, where the land is rising at a rate of as much as 8–9 mm per year, or 1 m in 100 years. This is important for archaeologists, since a site that was coastal in the Nordic Stone Age now is inland and can be dated by its relative distance from the present shore.

Würm glaciation (Alps)

 
Violet: extent of the Alpine ice sheet in the Würm glaciation. Blue: extent in earlier ice ages.

The term Würm is derived from a river in the Alpine foreland, roughly marking the maximum glacier advance of this particular glacial period. The Alps were where the first systematic scientific research on ice ages was conducted by Louis Agassiz at the beginning of the 19th century. Here, the Würm glaciation of the LGP was intensively studied. Pollen analysis, the statistical analyses of microfossilized plant pollens found in geological deposits, chronicled the dramatic changes in the European environment during the Würm glaciation. During the height of Würm glaciation, c. 24,000 – c. 10,000 BP, most of western and central Europe and Eurasia was open steppe-tundra, while the Alps presented solid ice fields and montane glaciers. Scandinavia and much of Britain were under ice.

During the Würm, the Rhône Glacier covered the whole western Swiss plateau, reaching today's regions of Solothurn and Aarau. In the region of Bern, it merged with the Aar glacier. The Rhine Glacier is currently the subject of the most detailed studies. Glaciers of the Reuss and the Limmat advanced sometimes as far as the Jura. Montane and piedmont glaciers formed the land by grinding away virtually all traces of the older Günz and Mindel glaciation, by depositing base moraines and terminal moraines of different retraction phases and loess deposits, and by the proglacial rivers' shifting and redepositing gravels. Beneath the surface, they had profound and lasting influence on geothermal heat and the patterns of deep groundwater flow.

North America

Pinedale or Fraser glaciation (Rocky Mountains)

 
Map of Pleistocene lakes in the Great Basin of western North America, showing the path of the Bonneville Flood along the Snake River

The Pinedale (central Rocky Mountains) or Fraser (Cordilleran ice sheet) glaciation was the last of the major glaciations to appear in the Rocky Mountains in the United States. The Pinedale lasted from around 30,000 to 10,000 years ago, and was at its greatest extent between 23,500 and 21,000 years ago.[40] This glaciation was somewhat distinct from the main Wisconsin glaciation, as it was only loosely related to the giant ice sheets and was instead composed of mountain glaciers, merging into the Cordilleran ice sheet.[41] The Cordilleran ice sheet produced features such as glacial Lake Missoula, which broke free from its ice dam, causing the massive Missoula Floods. USGS geologists estimate that the cycle of flooding and reformation of the lake lasted an average of 55 years and that the floods occurred about 40 times over the 2,000-year period starting 15,000 years ago.[42] Glacial lake outburst floods such as these are not uncommon today in Iceland and other places.

Wisconsin glaciation

The Wisconsin glacial episode was the last major advance of continental glaciers in the North American Laurentide ice sheet. At the height of glaciation, the Bering land bridge potentially permitted migration of mammals, including people, to North America from Siberia.

It radically altered the geography of North America north of the Ohio River. At the height of the Wisconsin episode glaciation, ice covered most of Canada, the Upper Midwest, and New England, as well as parts of Montana and Washington. On Kelleys Island in Lake Erie or in New York's Central Park, the grooves left by these glaciers can be easily observed. In southwestern Saskatchewan and southeastern Alberta, a suture zone between the Laurentide and Cordilleran ice sheets formed the Cypress Hills, which is the northernmost point in North America that remained south of the continental ice sheets.

The Great Lakes are the result of glacial scour and pooling of meltwater at the rim of the receding ice. When the enormous mass of the continental ice sheet retreated, the Great Lakes began gradually moving south due to isostatic rebound of the north shore. Niagara Falls is also a product of the glaciation, as is the course of the Ohio River, which largely supplanted the prior Teays River.

With the assistance of several very broad glacial lakes, it released floods through the gorge of the Upper Mississippi River, which in turn was formed during an earlier glacial period.

In its retreat, the Wisconsin episode glaciation left terminal moraines that form Long Island, Block Island, Cape Cod, Nomans Land, Martha's Vineyard, Nantucket, Sable Island, and the Oak Ridges Moraine in south-central Ontario, Canada. In Wisconsin itself, it left the Kettle Moraine. The drumlins and eskers formed at its melting edge are landmarks of the lower Connecticut River Valley.

Tahoe, Tenaya, and Tioga, Sierra Nevada

In the Sierra Nevada, three stages of glacial maxima (sometimes incorrectly called ice ages) were separated by warmer periods. These glacial maxima are called, from oldest to youngest, Tahoe, Tenaya, and Tioga.[43] The Tahoe reached its maximum extent perhaps about 70,000 years ago. Little is known about the Tenaya. The Tioga was the least severe and last of the Wisconsin episode. It began about 30,000 years ago, reached its greatest advance 21,000 years ago, and ended about 10,000 years ago.

Greenland glaciation

In northwest Greenland, ice coverage attained a very early maximum in the LGP around 114,000. After this early maximum, ice coverage was similar to today until the end of the last glacial period. Towards the end, glaciers advanced once more before retreating to their present extent.[44] According to ice core data, the Greenland climate was dry during the LGP, with precipitation reaching perhaps only 20% of today's value.[45]

South America

Mérida glaciation (Venezuelan Andes)

 
Map showing the extent of the glaciated area in Venezuelan Andes during the Mérida glaciation

The name Mérida glaciation is proposed to designate the alpine glaciation that affected the central Venezuelan Andes during the Late Pleistocene. Two main moraine levels have been recognized - one with an elevation of 2,600–2,700 m (8,500–8,900 ft), and another with an elevation of 3,000–3,500 m (9,800–11,500 ft). The snow line during the last glacial advance was lowered approximately 1,200 m (3,900 ft) below the present snow line, which is 3,700 m (12,100 ft). The glaciated area in the Cordillera de Mérida was about 600 km2 (230 sq mi); this included these high areas, from southwest to northeast: Páramo de Tamá, Páramo Batallón, Páramo Los Conejos, Páramo Piedras Blancas, and Teta de Niquitao. Around 200 km2 (77 sq mi) of the total glaciated area was in the Sierra Nevada de Mérida, and of that amount, the largest concentration, 50 km2 (19 sq mi), was in the areas of Pico Bolívar, Pico Humboldt [4,942 m (16,214 ft)], and Pico Bonpland [4,983 m (16,348 ft)]. Radiocarbon dating indicates that the moraines are older than 10,000 BP, and probably older than 13,000 BP. The lower moraine level probably corresponds to the main Wisconsin glacial advance. The upper level probably represents the last glacial advance (Late Wisconsin).[46][47][48][49][50]

Llanquihue glaciation (Southern Andes)

 
Map showing the extent of the Patagonian ice sheet in the Strait of Magellan area during the LGP: Selected modern settlements are shown with yellow dots.

The Llanquihue glaciation takes its name from Llanquihue Lake in southern Chile, which is a fan-shaped piedmont glacial lake. On the lake's western shores, large moraine systems occur, of which the innermost belong to the LGP. Llanquihue Lake's varves are a node point in southern Chile's varve geochronology. During the last glacial maximum, the Patagonian ice sheet extended over the Andes from about 35°S to Tierra del Fuego at 55°S. The western part appears to have been very active, with wet basal conditions, while the eastern part was cold-based. Cryogenic features such as ice wedges, patterned ground, pingos, rock glaciers, palsas, soil cryoturbation, and solifluction deposits developed in unglaciated extra-Andean Patagonia during the last glaciation, but not all these reported features have been verified.[51] The area west of Llanquihue Lake was ice-free during the last glacial maximum, and had sparsely distributed vegetation dominated by Nothofagus. Valdivian temperate rain forest was reduced to scattered remnants on the western side of the Andes.[52]

 
Modelled maximum extent of the Antarctic ice sheet 21,000 years before present

See also

Historical names of the "four major" glacials in four regions
Region Glacial 1 Glacial 2 Glacial 3 Glacial 4
Alps Günz Mindel Riss Würm
North Europe Eburonian Elsterian Saalian Weichselian
British Isles Beestonian Anglian Wolstonian Devensian
Midwest U.S. Nebraskan Kansan Illinoian Wisconsinan

Notes

  1. ^ Prior to the 2010s, considerable debate arose on whether Southern Africa was glaciated during the last glacial cycle or not.[29][30]
  2. ^ The former existence of large glaciers or deep snow cover over much of the Lesotho Highlands has been judged unlikely considering the lack of glacial morphology (e.g. rôche moutonnées) and the existence of periglacial regolith that has not been reworked by glaciers.[30] Estimates of the mean annual temperature in Southern Africa during the last glacial maximum indicate the temperatures were not low enough to initiate or sustain a widespread glaciation. The former existence of rock glaciers or large glaciers is, according to the same study, ruled out, because of a lack of conclusive field evidence and the implausibility of the 10–17°C temperature drop, relative to the present, that such features would imply.[29]

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  36. ^ Huybrechts, P. (2002). "Sea-level changes at the LGM from ice-dynamic reconstructions of the Greenland and Antarctic ice sheets during the glacial cycles" (PDF). Quaternary Science Reviews. 21 (1–3): 203–231. Bibcode:2002QSRv...21..203H. doi:10.1016/S0277-3791(01)00082-8.
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  39. ^ Davis, Owen K. (2003). . Introduction to Quaternary Ecology. University of Arizona. Archived from the original on July 27, 2017.
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Further reading

  • Bowen, D.Q. (1978). Quaternary geology: a stratigraphic framework for multidisciplinary work. Oxford UK: Pergamon Press. ISBN 978-0-08-020409-3.
  • Ehlers, J.; Gibbard, P. L., eds. (2004). Quaternary Glaciations: Extent and Chronology 2: Part II North America. Amsterdam: Elsevier. ISBN 978-0-444-51462-2.
  • Ehlers, J.; Gibbard, P. L., eds. (2004). Quaternary Glaciations: Extent and Chronology 3: Part III: South America, Asia, Africa, Australia, Antarctica. Amsterdam: Elsevier. ISBN 978-0-444-51593-3.
  • Gillespie, A. R., Porter, S. C.; Atwater, B. F. (2004). The Quaternary Period in the United States [of America]. Developments in Quaternary Science. Vol. 1. Amsterdam: Elsevier. ISBN 978-0-444-51471-4.{{cite book}}: CS1 maint: multiple names: authors list (link)
  • Harris, A. G.; Tuttle, E.; Tuttle, S. D. (1997). Geology of National Parks (5th ed.). Iowa: Kendall/Hunt. ISBN 978-0-7872-5353-0.
  • Kuhle, M. (1988). "The Pleistocene Glaciation of Tibet and the Onset of Ice Ages – An Autocycle HypothesisGeoJournal". GeoJournal. 17 (4): 581–596. doi:10.1007/BF00209444. S2CID 129234912.
  • Mangerud, J.; Ehlers, J.; Gibbard, P., eds. (2004). Quaternary Glaciations : Extent and Chronology 1: Part I Europe. Amsterdam: Elsevier. ISBN 978-0-444-51462-2.
  • Sibrava, V.; Bowen, D.Q; Richmond, G. M. (1986). "Quaternary Glaciations in the Northern Hemisphere". Quaternary Science Reviews. 5: 1–514. doi:10.1016/S0277-3791(86)80002-6.
  • Pielou, E. C. (1991). After the Ice Age : The Return of Life to Glaciated North America. Chicago IL: University Of Chicago Press. ISBN 978-0-226-66812-3.

External links

  • Pielou, E. C. After the Ice Age: The Return of Life to Glaciated North America (University of Chicago Press: 1992)
  • : Present state of knowledge
  • Ray, N.; Adams, J.M. (2001). "A GIS-based Vegetation Map of the World at the Last Glacial Maximum (25,000–15,000 BP)" (PDF). Internet Archaeology. 11.

last, glacial, period, last, glacial, redirects, here, period, maximum, glacier, extent, during, this, time, last, glacial, maximum, also, known, colloquially, last, simply, occurred, from, eemian, younger, dryas, encompassing, period, years, part, larger, seq. Last glacial redirects here For the period of maximum glacier extent during this time see Last Glacial Maximum The Last Glacial Period LGP also known colloquially as the last ice age or simply ice age 1 occurred from the end of the Eemian to the end of the Younger Dryas encompassing the period c 115 000 c 11 700 years ago The LGP is part of a larger sequence of glacial and interglacial periods known as the Quaternary glaciation which started around 2 588 000 years ago and is ongoing 2 The definition of the Quaternary as beginning 2 58 million years ago Mya is based on the formation of the Arctic ice cap The Antarctic ice sheet began to form earlier at about 34 Mya in the mid Cenozoic Eocene Oligocene extinction event The term Late Cenozoic Ice Age is used to include this early phase 3 The previous ice age the Saalian glaciation which ended about 128 000 years ago was more severe than the Last Glacial Period in some areas such as Britain but less severe in others Chronology of climatic events of importance for the last glacial period about the last 120 000 years During this last glacial period alternating episodes of glacier advance and retreat occurred Within the last glacial period the Last Glacial Maximum was approximately 22 000 years ago While the general pattern of global cooling and glacier advance was similar local differences in the development of glacier advance and retreat make comparing the details from continent to continent difficult see picture of ice core data below for differences Around 12 800 years ago the Younger Dryas the most recent glacial epoch began a coda to the preceding 100 000 year glacial period Its end about 11 550 years ago marked the beginning of the Holocene the current geological epoch From the point of view of human archaeology the LGP falls in the Paleolithic and early Mesolithic periods When the glaciation event started Homo sapiens was confined to lower latitudes and used tools comparable to those used by Neanderthals in western and central Eurasia and by Denisovans and Homo erectus in Asia Archaeological and genetic data suggest that the source populations of Paleolithic humans survived the LGP in sparsely wooded areas and dispersed through areas of high primary productivity while avoiding dense forest cover 4 Artist s impression of the last glacial period at glacial maximum 5 Contents 1 Origin and definition 2 Overview 2 1 Northern Hemisphere 2 2 Southern Hemisphere 3 Deglaciation 4 Named local glaciations 4 1 Antarctica 4 2 Europe 4 2 1 Devensian and Midlandian glaciation Britain and Ireland 4 2 2 Weichselian glaciation Scandinavia and northern Europe 4 2 3 Wurm glaciation Alps 4 3 North America 4 3 1 Pinedale or Fraser glaciation Rocky Mountains 4 3 2 Wisconsin glaciation 4 3 3 Tahoe Tenaya and Tioga Sierra Nevada 4 3 4 Greenland glaciation 4 4 South America 4 4 1 Merida glaciation Venezuelan Andes 4 4 2 Llanquihue glaciation Southern Andes 5 See also 6 Notes 7 References 8 Further reading 9 External linksOrigin and definition EditThe LGP is often colloquially referred to as the last ice age though the term ice age is not strictly defined and on a longer geological perspective the last few million years could be termed a single ice age given the continual presence of ice sheets near both poles Glacials are somewhat better defined as colder phases during which glaciers advance separated by relatively warm interglacials The end of the last glacial period which was about 10 000 years ago is often called the end of the ice age although extensive year round ice persists in Antarctica and Greenland Over the past few million years the glacial interglacial cycles have been paced by periodic variations in the Earth s orbit via Milankovitch cycles The LGP has been intensively studied in North America northern Eurasia the Himalayas and other formerly glaciated regions around the world The glaciations that occurred during this glacial period covered many areas mainly in the Northern Hemisphere and to a lesser extent in the Southern Hemisphere They have different names historically developed and depending on their geographic distributions Fraser in the Pacific Cordillera of North America Pinedale in the Central Rocky Mountains Wisconsinan or Wisconsin in central North America Devensian in the British Isles 6 Midlandian in Ireland Wurm in the Alps Merida in Venezuela Weichselian or Vistulian in Northern Europe and northern Central Europe Valdai in Russia and Zyryanka in Siberia Llanquihue in Chile and Otira in New Zealand The geochronological Late Pleistocene includes the late glacial Weichselian and the immediately preceding penultimate interglacial Eemian period Overview Edit Vegetation types at time of Last glacial maximum Last glacial period as seen in ice core data from Antarctica and Greenland Northern Hemisphere Edit Canada was nearly completely covered by ice as was the northern part of the United States both blanketed by the huge Laurentide Ice Sheet Alaska remained mostly ice free due to arid climate conditions Local glaciations existed in the Rocky Mountains and the Cordilleran ice sheet and as ice fields and ice caps in the Sierra Nevada in northern California 7 In northern Eurasia the Scandinavian ice sheet once again reached the northern parts of the British Isles Germany Poland and Russia extending as far east as the Taymyr Peninsula in western Siberia 8 The maximum extent of western Siberian glaciation was reached by about 18 000 to 17 000 BP thus later than in Europe 22 000 18 000 BP 9 Northeastern Siberia was not covered by a continental scale ice sheet 10 Instead large but restricted icefield complexes covered mountain ranges within northeast Siberia including the Kamchatka Koryak Mountains 11 12 The Arctic Ocean between the huge ice sheets of America and Eurasia was not frozen throughout but like today probably was covered only by relatively shallow ice subject to seasonal changes and riddled with icebergs calving from the surrounding ice sheets According to the sediment composition retrieved from deep sea cores even times of seasonally open waters must have occurred 13 Outside the main ice sheets widespread glaciation occurred on the highest mountains of the Alpide belt In contrast to the earlier glacial stages the Wurm glaciation was composed of smaller ice caps and mostly confined to valley glaciers sending glacial lobes into the Alpine foreland Local ice fields or small ice sheets could be found capping the highest massifs of the Pyrenees the Carpathian Mountains the Balkan mountains the Caucasus and the mountains of Turkey and Iran 14 In the Himalayas and the Tibetan Plateau there is evidence that glaciers advanced considerably particularly between 47 000 and 27 000 BP 15 but the exact ages 16 17 as well as the formation of a single contiguous ice sheet on the Tibetan Plateau is controversial 18 19 20 Other areas of the Northern Hemisphere did not bear extensive ice sheets but local glaciers were widespread at high altitudes Parts of Taiwan for example were repeatedly glaciated between 44 250 and 10 680 BP 21 as well as the Japanese Alps In both areas maximum glacier advance occurred between 60 000 and 30 000 BP 22 To a still lesser extent glaciers existed in Africa for example in the High Atlas the mountains of Morocco the Mount Atakor massif in southern Algeria and several mountains in Ethiopia Just south of the equator an ice cap of several hundred square kilometers was present on the east African mountains in the Kilimanjaro massif Mount Kenya and the Rwenzori Mountains which still bear relic glaciers today 23 Southern Hemisphere Edit Glaciation of the Southern Hemisphere was less extensive Ice sheets existed in the Andes Patagonian Ice Sheet where six glacier advances between 33 500 and 13 900 BP in the Chilean Andes have been reported 24 Antarctica was entirely glaciated much like today but unlike today the ice sheet left no uncovered area In mainland Australia only a very small area in the vicinity of Mount Kosciuszko was glaciated whereas in Tasmania glaciation was more widespread 25 An ice sheet formed in New Zealand covering all of the Southern Alps where at least three glacial advances can be distinguished 26 Local ice caps existed in the highest mountains of the island of New Guinea where temperatures were 5 to 6 C colder than at present 27 28 The main areas of Papua New Guinea where glaciers developed during the LGP were the Central Cordillera the Owen Stanley Range and the Saruwaged Range Mount Giluwe in the Central Cordillera had a more or less continuous ice cap covering about 188 km2 and extending down to 3200 3500 m 27 In Western New Guinea remnants of these glaciers are still preserved atop Puncak Jaya and Ngga Pilimsit 28 Small glaciers developed in a few favorable places in Southern Africa during the last glacial period 29 A B These small glaciers would have been located in the Lesotho Highlands and parts of the Drakensberg 31 32 The development of glaciers was likely aided in part due to shade provided by adjacent cliffs 32 Various moraines and former glacial niches have been identified in the eastern Lesotho Highlands a few kilometres west of the Great Escarpment at altitudes greater than 3 000 m on south facing slopes 31 Studies suggest that the annual average temperature in the mountains of Southern Africa was about 6 C colder than at present in line with temperature drops estimated for Tasmania and southern Patagonia during the same time This resulted in an environment of relatively arid periglaciation without permafrost but with deep seasonal freezing on south facing slopes Periglaciation in the eastern Drakensberg and Lesotho Highlands produced solifluction deposits and blockfields including blockstreams and stone garlands 29 30 Deglaciation Edit Temperature rise marking the end of the most recent ice age as derived from ice core data Main article Holocene glacial retreat See also Bolling Allerod warming Meltwater pulse 1A and Deglaciation Scientists from the Center for Arctic Gas Hydrate Environment and Climate at the University of Tromso published a study in June 2017 33 describing over a hundred ocean sediment craters some 3 000 m wide and up to 300 m deep formed by explosive eruptions of methane from destabilized methane hydrates following ice sheet retreat during the LGP around 12 000 years ago These areas around the Barents Sea still seep methane today The study hypothesized that existing bulges containing methane reservoirs could eventually have the same fate Named local glaciations EditAntarctica Edit During the last glacial period Antarctica was blanketed by a massive ice sheet much as it is today however the ice covered all land areas and extended into the ocean onto the middle and outer continental shelf 34 35 Counterintuitively though according to ice modeling done in 2002 ice over central East Antarctica was generally thinner than it is today 36 Europe Edit Devensian and Midlandian glaciation Britain and Ireland Edit British geologists refer to the LGP as the Devensian Irish geologists geographers and archaeologists refer to the Midlandian glaciation as its effects in Ireland are largely visible in the Irish Midlands The name Devensian is derived from the Latin Devenses people living by the Dee Deva in Latin a river on the Welsh border near which deposits from the period are particularly well represented 37 The effects of this glaciation can be seen in many geological features of England Wales Scotland and Northern Ireland Its deposits have been found overlying material from the preceding Ipswichian stage and lying beneath those from the following Holocene which is the current stage This is sometimes called the Flandrian interglacial in Britain The latter part of the Devensian includes pollen zones I IV the Allerod oscillation and Bolling oscillation and the Oldest Dryas Older Dryas and Younger Dryas cold periods Weichselian glaciation Scandinavia and northern Europe Edit Main article Weichselian glaciation Europe during the last glacial period Alternative names include Weichsel glaciation or Vistulian glaciation referring to the Polish River Vistula or its German name Weichsel Evidence suggests that the ice sheets were at their maximum size for only a short period between 25 000 and 13 000 BP Eight interstadials have been recognized in the Weichselian including the Oerel Glinde Moershoofd Hengelo and Denekamp however correlation with isotope stages is still in process 38 39 During the glacial maximum in Scandinavia only the western parts of Jutland were ice free and a large part of what is today the North Sea was dry land connecting Jutland with Britain see Doggerland The Baltic Sea with its unique brackish water is a result of meltwater from the Weichsel glaciation combining with saltwater from the North Sea when the straits between Sweden and Denmark opened Initially when the ice began melting about 10 300 BP seawater filled the isostatically depressed area a temporary marine incursion that geologists dub the Yoldia Sea Then as postglacial isostatic rebound lifted the region about 9500 BP the deepest basin of the Baltic became a freshwater lake in palaeological contexts referred to as Ancylus Lake which is identifiable in the freshwater fauna found in sediment cores The lake was filled by glacial runoff but as worldwide sea level continued rising saltwater again breached the sill about 8000 BP forming a marine Littorina Sea which was followed by another freshwater phase before the present brackish marine system was established At its present state of development the marine life of the Baltic Sea is less than about 4000 years old Drs Thulin and Andrushaitis remarked when reviewing these sequences in 2003 Overlying ice had exerted pressure on the Earth s surface As a result of melting ice the land has continued to rise yearly in Scandinavia mostly in northern Sweden and Finland where the land is rising at a rate of as much as 8 9 mm per year or 1 m in 100 years This is important for archaeologists since a site that was coastal in the Nordic Stone Age now is inland and can be dated by its relative distance from the present shore Wurm glaciation Alps Edit Main article Wurm glaciation Violet extent of the Alpine ice sheet in the Wurm glaciation Blue extent in earlier ice ages The term Wurm is derived from a river in the Alpine foreland roughly marking the maximum glacier advance of this particular glacial period The Alps were where the first systematic scientific research on ice ages was conducted by Louis Agassiz at the beginning of the 19th century Here the Wurm glaciation of the LGP was intensively studied Pollen analysis the statistical analyses of microfossilized plant pollens found in geological deposits chronicled the dramatic changes in the European environment during the Wurm glaciation During the height of Wurm glaciation c 24 000 c 10 000 BP most of western and central Europe and Eurasia was open steppe tundra while the Alps presented solid ice fields and montane glaciers Scandinavia and much of Britain were under ice During the Wurm the Rhone Glacier covered the whole western Swiss plateau reaching today s regions of Solothurn and Aarau In the region of Bern it merged with the Aar glacier The Rhine Glacier is currently the subject of the most detailed studies Glaciers of the Reuss and the Limmat advanced sometimes as far as the Jura Montane and piedmont glaciers formed the land by grinding away virtually all traces of the older Gunz and Mindel glaciation by depositing base moraines and terminal moraines of different retraction phases and loess deposits and by the proglacial rivers shifting and redepositing gravels Beneath the surface they had profound and lasting influence on geothermal heat and the patterns of deep groundwater flow North America Edit Pinedale or Fraser glaciation Rocky Mountains Edit Map of Pleistocene lakes in the Great Basin of western North America showing the path of the Bonneville Flood along the Snake River The Pinedale central Rocky Mountains or Fraser Cordilleran ice sheet glaciation was the last of the major glaciations to appear in the Rocky Mountains in the United States The Pinedale lasted from around 30 000 to 10 000 years ago and was at its greatest extent between 23 500 and 21 000 years ago 40 This glaciation was somewhat distinct from the main Wisconsin glaciation as it was only loosely related to the giant ice sheets and was instead composed of mountain glaciers merging into the Cordilleran ice sheet 41 The Cordilleran ice sheet produced features such as glacial Lake Missoula which broke free from its ice dam causing the massive Missoula Floods USGS geologists estimate that the cycle of flooding and reformation of the lake lasted an average of 55 years and that the floods occurred about 40 times over the 2 000 year period starting 15 000 years ago 42 Glacial lake outburst floods such as these are not uncommon today in Iceland and other places Wisconsin glaciation Edit The Wisconsin glacial episode was the last major advance of continental glaciers in the North American Laurentide ice sheet At the height of glaciation the Bering land bridge potentially permitted migration of mammals including people to North America from Siberia It radically altered the geography of North America north of the Ohio River At the height of the Wisconsin episode glaciation ice covered most of Canada the Upper Midwest and New England as well as parts of Montana and Washington On Kelleys Island in Lake Erie or in New York s Central Park the grooves left by these glaciers can be easily observed In southwestern Saskatchewan and southeastern Alberta a suture zone between the Laurentide and Cordilleran ice sheets formed the Cypress Hills which is the northernmost point in North America that remained south of the continental ice sheets The Great Lakes are the result of glacial scour and pooling of meltwater at the rim of the receding ice When the enormous mass of the continental ice sheet retreated the Great Lakes began gradually moving south due to isostatic rebound of the north shore Niagara Falls is also a product of the glaciation as is the course of the Ohio River which largely supplanted the prior Teays River With the assistance of several very broad glacial lakes it released floods through the gorge of the Upper Mississippi River which in turn was formed during an earlier glacial period In its retreat the Wisconsin episode glaciation left terminal moraines that form Long Island Block Island Cape Cod Nomans Land Martha s Vineyard Nantucket Sable Island and the Oak Ridges Moraine in south central Ontario Canada In Wisconsin itself it left the Kettle Moraine The drumlins and eskers formed at its melting edge are landmarks of the lower Connecticut River Valley Tahoe Tenaya and Tioga Sierra Nevada Edit In the Sierra Nevada three stages of glacial maxima sometimes incorrectly called ice ages were separated by warmer periods These glacial maxima are called from oldest to youngest Tahoe Tenaya and Tioga 43 The Tahoe reached its maximum extent perhaps about 70 000 years ago Little is known about the Tenaya The Tioga was the least severe and last of the Wisconsin episode It began about 30 000 years ago reached its greatest advance 21 000 years ago and ended about 10 000 years ago Greenland glaciation Edit In northwest Greenland ice coverage attained a very early maximum in the LGP around 114 000 After this early maximum ice coverage was similar to today until the end of the last glacial period Towards the end glaciers advanced once more before retreating to their present extent 44 According to ice core data the Greenland climate was dry during the LGP with precipitation reaching perhaps only 20 of today s value 45 South America Edit Merida glaciation Venezuelan Andes Edit Map showing the extent of the glaciated area in Venezuelan Andes during the Merida glaciation The name Merida glaciation is proposed to designate the alpine glaciation that affected the central Venezuelan Andes during the Late Pleistocene Two main moraine levels have been recognized one with an elevation of 2 600 2 700 m 8 500 8 900 ft and another with an elevation of 3 000 3 500 m 9 800 11 500 ft The snow line during the last glacial advance was lowered approximately 1 200 m 3 900 ft below the present snow line which is 3 700 m 12 100 ft The glaciated area in the Cordillera de Merida was about 600 km2 230 sq mi this included these high areas from southwest to northeast Paramo de Tama Paramo Batallon Paramo Los Conejos Paramo Piedras Blancas and Teta de Niquitao Around 200 km2 77 sq mi of the total glaciated area was in the Sierra Nevada de Merida and of that amount the largest concentration 50 km2 19 sq mi was in the areas of Pico Bolivar Pico Humboldt 4 942 m 16 214 ft and Pico Bonpland 4 983 m 16 348 ft Radiocarbon dating indicates that the moraines are older than 10 000 BP and probably older than 13 000 BP The lower moraine level probably corresponds to the main Wisconsin glacial advance The upper level probably represents the last glacial advance Late Wisconsin 46 47 48 49 50 Llanquihue glaciation Southern Andes Edit Main article Llanquihue glaciation Map showing the extent of the Patagonian ice sheet in the Strait of Magellan area during the LGP Selected modern settlements are shown with yellow dots The Llanquihue glaciation takes its name from Llanquihue Lake in southern Chile which is a fan shaped piedmont glacial lake On the lake s western shores large moraine systems occur of which the innermost belong to the LGP Llanquihue Lake s varves are a node point in southern Chile s varve geochronology During the last glacial maximum the Patagonian ice sheet extended over the Andes from about 35 S to Tierra del Fuego at 55 S The western part appears to have been very active with wet basal conditions while the eastern part was cold based Cryogenic features such as ice wedges patterned ground pingos rock glaciers palsas soil cryoturbation and solifluction deposits developed in unglaciated extra Andean Patagonia during the last glaciation but not all these reported features have been verified 51 The area west of Llanquihue Lake was ice free during the last glacial maximum and had sparsely distributed vegetation dominated by Nothofagus Valdivian temperate rain forest was reduced to scattered remnants on the western side of the Andes 52 Modelled maximum extent of the Antarctic ice sheet 21 000 years before presentSee also EditHistorical names of the four major glacials in four regions Region Glacial 1 Glacial 2 Glacial 3 Glacial 4Alps Gunz Mindel Riss WurmNorth Europe Eburonian Elsterian Saalian WeichselianBritish Isles Beestonian Anglian Wolstonian DevensianMidwest U S Nebraskan Kansan Illinoian WisconsinanGlacial history of Minnesota Glacial lake outburst flood Glacial period Penultimate Glacial Period Pleistocene which includes Pleistocene megafauna Plio Pleistocene Quaternary extinction event Quaternary glaciation Sea level rise Stone Age Timeline of glaciation Valparaiso MoraineNotes Edit Prior to the 2010s considerable debate arose on whether Southern Africa was glaciated during the last glacial cycle or not 29 30 The former existence of large glaciers or deep snow cover over much of the Lesotho Highlands has been judged unlikely considering the lack of glacial morphology e g roche moutonnees and the existence of periglacial regolith that has not been reworked by glaciers 30 Estimates of the mean annual temperature in Southern Africa during the last glacial maximum indicate the temperatures were not low enough to initiate or sustain a widespread glaciation The former existence of rock glaciers or large glaciers is according to the same study ruled out because of a lack of conclusive field evidence and the implausibility of the 10 17 C temperature drop relative to the present that such features would imply 29 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Template Cite journal cite journal a Cite journal requires journal help Schubert Carlos 1998 Glaciers of Venezuela US Geological Survey USGS P 1386 I Schubert C Valastro S 1974 Late Pleistocene glaciation of Paramo de La Culata north central Venezuelan Andes Geologische Rundschau 63 2 516 538 Bibcode 1974GeoRu 63 516S doi 10 1007 BF01820827 S2CID 129027718 Mahaney William C Milner M W Kalm Volli Dirsowzky Randy W Hancock R G V Beukens Roelf P April 1 2008 Evidence for a Younger Dryas glacial advance in the Andes of northwestern Venezuela Geomorphology 96 1 2 199 211 Bibcode 2008Geomo 96 199M doi 10 1016 j geomorph 2007 08 002 a href Template Cite journal html title Template Cite journal cite journal a CS1 maint multiple names authors list link Maximiliano B Orlando G Juan C Ciro S Glacial Quaternary geology of las Gonzales basin paramo los conejos Venezuelan andes Trombotto Liaudat Dario 2008 Geocryology of Southern South America In Rabassa J ed The Late Cenozoic of Patagonia and Tierra del Fuego pp 255 268 ISBN 978 0 444 52954 1 Adams Jonathan South America during the last 150 000 years Archived from the original on January 30 2010 Further reading EditBowen D Q 1978 Quaternary geology a stratigraphic framework for multidisciplinary work Oxford UK Pergamon Press ISBN 978 0 08 020409 3 Ehlers J Gibbard P L eds 2004 Quaternary Glaciations Extent and Chronology 2 Part II North America Amsterdam Elsevier ISBN 978 0 444 51462 2 Ehlers J Gibbard P L eds 2004 Quaternary Glaciations Extent and Chronology 3 Part III South America Asia Africa Australia Antarctica Amsterdam Elsevier ISBN 978 0 444 51593 3 Gillespie A R Porter S C Atwater B F 2004 The Quaternary Period in the United States of America Developments in Quaternary Science Vol 1 Amsterdam Elsevier ISBN 978 0 444 51471 4 a href Template Cite book html title Template Cite book cite book a CS1 maint multiple names authors list link Harris A G Tuttle E Tuttle S D 1997 Geology of National Parks 5th ed Iowa Kendall Hunt ISBN 978 0 7872 5353 0 Kuhle M 1988 The Pleistocene Glaciation of Tibet and the Onset of Ice Ages An Autocycle HypothesisGeoJournal GeoJournal 17 4 581 596 doi 10 1007 BF00209444 S2CID 129234912 Mangerud J Ehlers J Gibbard P eds 2004 Quaternary Glaciations Extent and Chronology 1 Part I Europe Amsterdam Elsevier ISBN 978 0 444 51462 2 Sibrava V Bowen D Q Richmond G M 1986 Quaternary Glaciations in the Northern Hemisphere Quaternary Science Reviews 5 1 514 doi 10 1016 S0277 3791 86 80002 6 Pielou E C 1991 After the Ice Age The Return of Life to Glaciated North America Chicago IL University Of Chicago Press ISBN 978 0 226 66812 3 External links EditPielou E C After the Ice Age The Return of Life to Glaciated North America University of Chicago Press 1992 National Atlas of the USA Wisconsin Glaciation in North America Present state of knowledge Ray N Adams J M 2001 A GIS based Vegetation Map of the World at the Last Glacial Maximum 25 000 15 000 BP PDF Internet Archaeology 11 Retrieved from https en wikipedia org w index php title Last Glacial Period amp oldid 1132380254, wikipedia, wiki, book, books, library,

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