The Last Glacial Period (LGP) occurred from the end of the Eemian interglacial to the end of the Younger Dryas, encompassing the period c. 115,000 – c. 11,700 years ago. This most recent glacial period is part of a larger pattern of glacial and interglacial periods known as the Quaternary glaciation extending from c. 2,588,000 years ago to present. The definition of the Quaternary as beginning 2.58 Ma is based on the formation of the Arctic ice cap. The Antarctic ice sheet began to form earlier, at about 34 Ma, in the mid-Cenozoic (Eocene–Oligocene extinction event). The term Late Cenozoic Ice Age is used to include this early phase.
During this last glacial period there were alternating episodes of glacier advance and retreat. 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 it difficult to compare the details from continent to continent (see picture of ice core data below for differences). Approximately 13,000 years ago, the Late Glacial Maximum began. The end of the Younger Dryas about 11,700 years ago marked the beginning of the Holocene geological epoch, which includes the Holocene glacial retreat.
From the point of view of human archaeology, the last glacial period falls in the Paleolithic and early Mesolithic periods. When the glaciation event started, Homo sapiens were confined to lower latitudes and used tools comparable to those used by Neanderthals in western and central Eurasia and by Homo erectus in Asia. Near the end of the event, Homo sapiens migrated into Eurasia and Australia. Archaeological and genetic data suggest that the source populations of Paleolithic humans survived the last glacial period in sparsely wooded areas and dispersed through areas of high primary productivity while avoiding dense forest cover.
The last glacial period is sometimes colloquially referred to as the "last ice age", though this use is incorrect because an ice age is a longer period of cold temperature in which year-round ice sheets are present near one or both poles. Glacials are colder phases within an ice age in which glaciers advance; glacials are separated by interglacials. Thus, the end of the last glacial period, which was about 11,700 years ago, is not the end of the last ice age since 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 last glacial period is the best-known part of the current ice age, and has been intensively studied in North America, northern Eurasia, the Himalaya 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), 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.
Canada was nearly completely covered by ice, as well as 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. In Britain, mainland Europe, and northwestern Asia, 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. The maximum extent of western Siberian glaciation was reached by approximately 16,000–15,000 BC and thus later than in Europe (c. 20,000 – c. 16,000 BC). Northeastern Siberia was not covered by a continental-scale ice sheet. Instead, large, but restricted, icefield complexes covered mountain ranges within northeast Siberia, including the Kamchatka-Koryak Mountains.
The Arctic Ocean between the huge ice sheets of America and Eurasia was not frozen throughout, but like today probably was only covered 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 there must even have been times of seasonally open waters.
Outside the main ice sheets, widespread glaciation occurred on the highest mountains of the Alps−Himalaya mountain chain. 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. The [[Pirenees], the highest massifs of the Carpathian Mountains and the Balkanic peninsula mountains and to the east the Caucasus and the mountains of Turkey and Iran were capped by local ice fields or small ice sheets.
In the Himalaya and the Tibetan Plateau, glaciers advanced considerably, particularly between 45,000 and 25,000 BC, but these datings are controversial. The formation of a contiguous ice sheet on the Tibetan Plateau is controversial.
Other areas of the Northern Hemisphere did not bear extensive ice sheets, but local glaciers in high areas. Parts of Taiwan, for example, were repeatedly glaciated between 42,250 and 8,680 BCE as well as the Japanese Alps. In both areas maximum glacier advance occurred between 58,000 and 28,000 BCE. 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. In the Southern Hemisphere, 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, still bearing remnants of glaciers today.
Glaciation of the Southern Hemisphere was less extensive because of current configuration of continents. Ice sheets existed in the Andes (Patagonian Ice Sheet), where six glacier advances between 31,500 and 11,900 BC in the Chilean Andes have been reported. Antarctica was entirely glaciated, much like today, but 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. An ice sheet formed in New Zealand, covering all of the Southern Alps, where at least three glacial advances can be distinguished. Local ice caps existed in Irian Jaya, Indonesia, where in three ice areas remnants of the Pleistocene glaciers are still preserved today.
Small glaciers developed in a few favorable places in Southern Africa during the last glacial period.[A][B] These small glaciers would have developed in the Lesotho Highlands and parts of the Drakensberg. The development of glaciers was likely aided by localized cooling indebted to shading by adjacent cliffs. Various moraines and former glacier niches have been identified in the eastern Lesotho Highlands, above 3,000 m.a.s.l. and on south-facing slopes, a few kilometres west of the Great Escarpment. Studies suggest the mountains of Southern Africa were mostly subject to mild periglaciation during the last glacial cycle and the annual average temperatures were about 6 °C colder than at present. The estimated 6 °C temperature drop for Southern Africa is in line with temperature drops estimated for Tasmania and southern Patagonia during the same time. The environment of the Lesotho Highlands during the Last Glacial Maximum was one of a 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, blockfields and blockstreams, and stone garlands.
Scientists from the Center for Arctic Gas Hydrate, Environment (CAGE) and Climate at the Arctic University of Norway, published a study in June 2017 describing over a hundred ocean sediment craters, some 3,000 meters wide and up to 300 meters deep, formed by explosive eruptions of methane from destabilized methane hydrates, following ice-sheet retreat during the last glacial period, 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.
During the last glacial period Antarctica was blanketed by a massive ice sheet, much as it is today. The ice covered all land areas and extended into the ocean onto the middle and outer continental shelf. According to ice modelling, ice over central East Antarctica was generally thinner than today.
British geologists refer to the last glacial period 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.
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 stage we are living in today. This is sometimes called the Flandrian interglacial in Britain.
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. 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). It is also in Denmark that the only Scandinavian ice-age animals older than 13,000 BCE are found.
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 post-glacial 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 meter 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.
The term Würm is derived from a river in the Alpine foreland, approximately 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 last glacial period 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 pro-glacial rivers' shifting and redepositing gravels. Beneath the surface, they had profound and lasting influence on geothermal heat and the patterns of deep groundwater flow.
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 approximately 30,000 to 10,000 years ago and was at its greatest extent between 23,500 and 21,000 years ago. 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. The Cordilleran Ice Sheet produced features such as glacial Lake Missoula, which would break 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 approximately 40 times over the 2,000 year period between 15,000 and 13,000 years ago. Glacial lake outburst floods such as these are not uncommon today in Iceland and other places.
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.
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.
In the Sierra Nevada, there are three named stages of glacial maxima (sometimes incorrectly called ice ages) separated by warmer periods. These glacial maxima are called, from oldest to youngest, Tahoe, Tenaya, and Tioga. 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.
In Northwest Greenland, ice coverage attained a very early maximum in the last glacial period around 114,000. After this early maximum, the ice coverage was similar to today until the end of the last glacial period. Towards the end, glaciers readvanced once more before retreating to their present extent. According to ice core data, the Greenland climate was dry during the last glacial period, precipitation reaching perhaps only 20% of today's value.
The name Mérida Glaciation is proposed to designate the alpine glaciation which 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 approximately 600 km2 (230 sq mi); this included the following high areas from southwest to northeast: Páramo de Tamá, Páramo Batallón, Páramo Los Conejos, Páramo Piedras Blancas, and Teta de Niquitao. Approximately 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).
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 there are large moraine systems of which the innermost belong to the last glacial period. 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 like ice wedges, patterned ground, pingos, rock glaciers, palsas, soil cryoturbation, solifluction deposits developed in unglaciated extra-Andean Patagonia during the Last Glaciation. However, not all these reported features have been verified. The area west of Llanquihue Lake was ice-free during the LGM, and had sparsely distributed vegetation dominated by Nothofagus. Valdivian temperate rain forest was reduced to scattered remnants in the western side of the Andes.
Asham Quarry is a 2.6-hectare (6.4-acre) geological Site of Special Scientific Interest north of Newhaven in East Sussex. It is a Geological Conservation Review site and in the Sussex Downs Area of Outstanding Natural Beauty.This site provides important biostratigraphical and lithostratigraphical evidence about environmental conditions during the last 100,000 years, the Last Glacial Period and the Holocene. It is notable for its extensive early and mid Holocene deposits and for having yielded a series of radiocarbon dates.Boggeragh Mountains
The Boggeragh Mountains (Irish: An Bhograch) are located in County Cork, Ireland, with the Munster Blackwater to the north and the River Lee to the south of the hills. With an elevation of 644 m (2,113 ft), the highest peak is Musheramore (Irish: Muisire Mór). The landscape consists of peat blanket bog, grassland, streams and areas of forestry. The mountains were formed from red sandstone deposited during the Devonian Era. They were shaped by glacial erosion during the last glacial period.
Construction of a wind farm in the area started in September 2009. In February 2010 19 units of Vestas V90-3MW MW wind turbines are up and running.Cedar Hill (Central Park)
Cedar Hill in Central Park, New York City, is an east-facing slope used for reading and sunbathing, sledding in winter and a preferred area for dog owners. The hill indeed is home to many red cedars that form a line of clumps on its crest. Low outcroppings of rock in the mown turf were grooved and scarred by the last glacial period. The south slope is called by joggers "Cat Hill" for its statue, 'Still Hunt', of a large stalking cat. Eddie Coyle, a sportswriter for the New York Daily News, in his weekly running columns in the late 1970s, often called it "cat" Hill and the name became popular.
The frontage of Fifth Avenue apartment houses provides a backdrop to the east. At its southern perimeter stands the Glade Arch designed by Calvert Vaux, which originally provided carriage traffic with a conduit to Fifth Avenue. Hidden deep beneath the north end of Cedar Hill runs New York City Water Tunnel No. 3 with its valve chamber, completed in 1993, due to carry some of the city's drinking water in 2020.Eemian
The Eemian (also called the last interglacial, Sangamonian Stage, Ipswichian, Mikulin, Kaydaky, penultimate, Valdivia or Riss-Würm) was the interglacial period which began about 130,000 years ago at the end of the Penultimate Glacial Period and ended about 115,000 years ago at the beginning of the Last Glacial Period. It corresponds to Marine Isotope Stage 5e. Although sometimes referred to as the "last interglacial" (in the "most recent previous" sense of "last"), it was the second-to-latest interglacial period of the current Ice Age, the most recent being the Holocene which extends to the present day (having followed the last glacial period). The prevailing Eemian climate was, on average, around 1 to 2 degrees Celsius (1.8 to 3.6 Fahrenheit) warmer than that of the Holocene. However, due to global warming, the past few July global temperatures likely surpassed the (long-term average) July temperatures of the Eemian period. During the Eemian, the proportion of CO2 in the atmosphere was about 280 parts per million.The Eemian is known as the Ipswichian in the UK, the Mikulin interglacial in Russia, the Valdivia interglacial in Chile and the Riss-Würm interglacial in the Alps. Depending on how a specific publication defines the Sangamonian Stage of North America, the Eemian is equivalent to either all or part of it.Geology of Florida
The Floridian peninsula is a porous plateau of karst limestone sitting atop bedrock known as the Florida Platform. The emergent portion of the platform was created during the Eocene to Oligocene as the Gulf Trough filled with silts, clays, and sands. Flora and fauna began appearing during the Miocene. No land animals were present in Florida prior to the Miocene.
The largest deposits of rock phosphate in the country are found in Florida. Most of this is in Bone Valley.Extended systems of underwater caves, sinkholes and springs are found throughout the state and supply most of the water used by residents. The limestone is topped with sandy soils deposited as ancient beaches over millions of years as global sea levels rose and fell. During the last glacial period, lower sea levels and a drier climate revealed a much wider peninsula, largely savanna.
While there are sinkholes in much of the state, modern sinkholes have tended to be in West-Central Florida.Glacial period
A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate between glacial periods. The last glacial period ended about 15,000 years ago. The Holocene epoch is the current interglacial. A time with no glaciers on Earth is considered a greenhouse climate state.Heinrich event
A Heinrich event is a natural phenomenon in which large armadas of icebergs break off from glaciers and traverse the North Atlantic. First described by marine geologist Hartmut Heinrich (Heinrich, H., 1988), they occurred during five of the last seven glacial periods or "ice ages" over the past 640,000 years (Hodell, et al., 2008). Heinrich events are particularly well documented for the last glacial period but notably absent from the penultimate glaciation (Obrochta et al., 2014). The icebergs contained rock mass, eroded by the glaciers, and as they melted, this material was dropped to the sea floor as ice rafted debris (abbreviated to "IRD").
The icebergs' melting caused extensive amounts of fresh water to be added to the North Atlantic. Such inputs of cold and fresh water may well have altered the density-driven, thermohaline circulation patterns of the ocean, and often coincide with indications of global climate fluctuations.
Various mechanisms have been proposed to explain the cause of Heinrich events, most of which imply instability of the massive Laurentide ice sheet, a continental glacier covering north eastern North America during the last glacial period. Other northern hemisphere ice sheets were potentially involved as well (Fennoscandic, Iceland/Greenland). However, the initial cause of this instability is still debated.Holkham Brick Pit
Holkham Brick Pit is a 0.5-hectare (1.2-acre) geological Site of Special Scientific Interest west of Wells-next-the-Sea in Norfolk. It is a Geological Conservation Review site, and it is in the Norfolk Coast Area of Outstanding Natural Beauty.This is the best site displaying the Hunstanton Till, a glacial deposit dating the last glacial period, between 115,000 and 11,700 years ago. This is the furthest the ice reached in East Anglia during the Last Glacial Maximum, around 26,000 years ago.The site is private land with no public access, and no geology is visible as the pit has been filled in.Holocene
The Holocene ( ) 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. The Holocene and the preceding Pleistocene 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.The Holocene has seen the growth and impacts of the human species worldwide, including all its written history, development of major civilizations, and overall significant transition toward urban living in the present. Human impacts on modern-era Earth and its ecosystems may be considered of global significance for future evolution of living species, including approximately synchronous lithospheric evidence, or more recently hydrospheric and atmospheric evidence of human impacts. In July 2018, the International Union of Geological Sciences split the Holocene epoch into three distinct subsections, Greenlandian (11,700 years ago to 8,326 years ago), Northgrippian (8,326 years ago to 4,200 years ago) and Meghalayan (4,200 years ago to the present), as proposed by International Commission on Stratigraphy. The boundary stratotype of Meghalayan is a speleothem in Mawmluh cave in India, and the global auxiliary stratotype is an ice core from Mount Logan in Canada.The name Holocene comes from the Ancient Greek words ὅλος (holos, whole or entire) and καινός (kainos, new), meaning "entirely recent".Houlder and Monarch Hill Pits, Upper Halling
Houlder and Monarch Hill Pits is a 0.7-hectare (1.7-acre) geological Site of Special Scientific Interest in Upper Halling in Kent. It is a Geological Conservation Review site.This site has a sequence of deposits covering the end of the Last glacial period, with two sheets of glacial deposits separated by a fossil soil assigned to the late glacial interstadial around 13,000 years ago. It provides evidence of lithostratigraphic and biostratigraphic changes during this period.The quarries are private land with no public access.Hyaloclastite
Hyaloclastite is a volcaniclastic accumulation or breccia consisting of glass (from the Greek hyalus) fragments (clasts) formed by quench fragmentation of lava flow surfaces during submarine or subglacial extrusion. It occurs as thin margins on the lava flow surfaces and between pillow lavas as well as in thicker deposits, more commonly associated with explosive, volatile-rich eruptions as well as steeper topography. Hyaloclastites form during volcanic eruptions under water, under ice or where subaerial flows reach the sea or other bodies of water. It commonly has the appearance of angular flat fragments sized between a millimeter to few centimeters. The fragmentation occurs by the force of the volcanic explosion, or by thermal shock and spallation during rapid cooling.
Several minerals are found in hyaloclastite masses. Sideromelane is a basalt glass rapidly quenched in water. It is transparent and pure, lacking the iron oxide crystals dispersed in the more commonly occurring tachylite. Fragments of these glasses are usually surrounded by a yellow waxy layer of palagonite, formed by reaction of sideromelane with water.
Hyaloclastite ridges, formed by subglacial eruptions during the last glacial period, are a prominent landscape feature of Iceland and the Canadian province of British Columbia. Hyaloclastite is usually found at subglacial volcanoes, such as tuyas, which is a type of distinctive, flat-topped, steep-sided volcano formed when lava erupts through a thick glacier or ice sheet.
In lava deltas, hyaloclastites form the main constituent of foresets formed ahead of the expanding delta. The foresets fill in the seabed topography, eventually building up to sea level, allowing the subaerial flow to move forwards until it reaches the sea again.Ice sheet
An ice sheet, also known as a continental glacier, is a mass of glacial ice that covers surrounding terrain and is greater than 50,000 km2 (19,000 sq mi). The only current ice sheets are in Antarctica and Greenland; during the last glacial period at Last Glacial Maximum (LGM) the Laurentide ice sheet covered much of North America, the Weichselian ice sheet covered northern Europe and the Patagonian Ice Sheet covered southern South America.
Ice sheets are bigger than ice shelves or alpine glaciers. Masses of ice covering less than 50,000 km2 are termed an ice cap. An ice cap will typically feed a series of glaciers around its periphery.
Although the surface is cold, the base of an ice sheet is generally warmer due to geothermal heat. In places, melting occurs and the melt-water lubricates the ice sheet so that it flows more rapidly. This process produces fast-flowing channels in the ice sheet — these are ice streams.
The present-day polar ice sheets are relatively young in geological terms. The Antarctic Ice Sheet first formed as a small ice cap (maybe several) in the early Oligocene, but retreating and advancing many times until the Pliocene, when it came to occupy almost all of Antarctica. The Greenland ice sheet did not develop at all until the late Pliocene, but apparently developed very rapidly with the first continental glaciation. This had the unusual effect of allowing fossils of plants that once grew on present-day Greenland to be much better preserved than with the slowly forming Antarctic ice sheet.Ingression coast
An ingression coast or depressed coast is a generally level coastline that is shaped by the penetration of the sea as a result of crustal movements or a rise in the sea level.
Such coasts are characterised by a subaerially formed relief that has previously experienced little deformation by littoral (tidal) processes, because the sea level, which had fallen by more than 100 metres during the last glacial period, did not reach its current level until about 6,000 years ago.
Depending on the geomorphological shaping of the flooded landform – e. g. glacially or fluvially formed relief – various types of ingression coast emerge, such as rias, skerry and fjard coasts as well as förde and bodden coasts.Llanquihue Lake
Lake Llanquihue is the second largest lake in Chile with an area of about 860 square kilometres (330 sq mi). It is situated in the southern Los Lagos Region in the Llanquihue and Osorno provinces. The lake's fan-like form was created by successive piedmont glaciers during the Quaternary glaciations. The last glacial period is called Llanquihue glaciation in Chile after the terminal moraine systems around the lake.Lake Llanquihue is located in southern Chile a territory of northern Patagonia in the Los Lagos Region. The lake's views of Volcán Osorno make the surrounding cities such as Puerto Varas tourism hotspots.Mansfield Hollow State Park
Mansfield Hollow State Park is a public recreation area occupying 251 acres (102 ha) of leased lands on the western shore of 500-acre (200 ha) Mansfield Hollow Lake in the town of Mansfield, Connecticut. The state park is one portion of the 2,300 acres (930 ha) leased by the Connecticut Department of Energy and Environmental Protection from the U.S. Army Corps of Engineers for recreational and wildlife management purposes. Geologic features of the park include remnants of the last glacial period, where retreating glaciers left kames, eskers, and kettles. Recreational opportunities include facilities for boating, fishing, picnicking, hiking, mountain biking, and cross-country skiing. The park is traversed by the southeastern leg of the Nipmuck Trail.Mount Brew (Cheakamus River)
Mount Brew is a rounded mountain in southwestern British Columbia, Canada, located 18 km (11 mi) southwest of Whistler in the Pacific Ranges of the Coast Mountains. A public cabin run by the Varsity Outdoor Club, Brew Hut, is located near the summit. The alpine area is a popular destination for hiking in the summer and backcountry ski touring in the winter and spring.
Mount Brew is a volcanic feature in the Mount Cayley volcanic field of the central Garibaldi Volcanic Belt of the Canadian Cascade Arc. It formed during the Pleistocene period when volcanic activity in this area occurred under glacial ice during the last glacial period. Although it had a vigorous start, the eruption that formed Mount Brew was not sufficiently sustained to form a larger edifice that could break through the surrounding ice and water to form a tuya. Instead, the eruption produced a subglacial mound.Penultimate Glacial Period
The Penultimate Glacial Period (PGP) is the glacial period that occurred before the last glacial period. It began ~194,000 years ago, and ended 135,000 years ago with the beginning of the Eemian interglacial. It roughly coincides with Marine Isotope Stage 6 (see Marine Isotope Stage) and the Illinoian Stage. The penultimate glacial period is one of a series of glacial and interglacial periods of the Quaternary Ice Age/Quaternary Glaciation. The Quaternary Ice Age began 2.58 million years ago and is ongoing. It began with the formation of the Arctic Ice Cap. The Quaternary Ice Age is part of an even longer ice age called the Late Cenozoic Ice Age. It began 33.9 million years ago and is also ongoing. It began with the formation of the Antarctic Ice Cap.Just like the Last Glacial Period, the penultimate glacial period has no name. The word penultimate means second to last.
The penultimate glacial period was at least the second glacial period that Neanderthals and Homo sapiens experienced.
Penultimate Glacial Period was more severe than the Last Glacial Period.Quaternary
Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.588 ± 0.005 million years ago to the present. 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). The informal term "Late Quaternary" refers to the past 0.5–1.0 million years.The Quaternary Period is typically defined by the cyclic growth and decay of continental ice sheets associated with Milankovitch cycles and the associated climate and environmental changes that occurred.Sundaland
Sundaland (also called the Sundaic region) is a biogeographical region of Southeastern Asia corresponding to a larger landmass that was exposed throughout the last 2.6 million years during periods when sea levels were lower. It includes the Malay Peninsula on the Asian mainland, as well as the large islands of Borneo, Java, and Sumatra and their surrounding islands.
|Quaternary / |