Cordilleran ice sheet

Cordilleran Ice Sheet
Cordilleran Ice Sheet
	Map of North America during the Last Glacial Maximum, showing Cordilleran ice sheet (left) at maximum extent
Type	continental
Location	North American Cordillera
Area	1,500,000 km2
Width	900 km
Lowest elevation	Sea level
Terminus	West – Pacific Ocean ; East – Great Plains ; South – 40 degrees north latitude
Status	gone

Last updated December 07, 2024

The Cordilleran ice sheet was a major ice sheet that periodically covered large parts of North America during glacial periods over the last ~2.6 million years.

Extent

The ice extent covered almost all of the continental shelf north of the Strait of Juan de Fuca and south from approximately the southwestern third of the Yukon Territory. This included all of mainland British Columbia, South Central Alaska, the Alaska Panhandle, and peninsula. The southern glacial maximums extended south to Washington state near Olympia in the west and to Spokane, the Idaho Panhandle, and much of Western Montana at the eastern glacial edge. At its eastern end the Cordilleran ice sheet merged with the Laurentide Ice Sheet at the Continental Divide, forming an area of ice that contained one and a half times as much water as the Antarctic ice sheet does today. The ice sheet faded north of the Alaska Range because the climate was too dry to form glaciers.^{[ citation needed ]}

The ice sheet covered up to 1,500,000 km² (580,000 sq mi) at the Last Glacial Maximum ^[1] and probably more than that in some previous periods, when it may have extended into the northeast extremity of Oregon and the Salmon River Mountains in Idaho. It is probable, though, that its northern margin also migrated south due to the influence of starvation caused by very low levels of precipitation.^{[ citation needed ]}

Refugia

At its western end it is currently understood that several small glacial refugia existed during the last glacial maximum below present sea level in the now-submerged Hecate Strait and on the Brooks Peninsula in northern Vancouver Island. However, evidence of ice-free refugia above present sea level north of the Olympic Peninsula has been refuted by genetic and geological studies since the middle 1990s.

Thawing

Unlike the Laurentide Ice Sheet, which may have taken as many as eleven thousand years to fully melt,^[2] the Cordilleran ice sheet melted very quickly, probably in four thousand years or less.^[3] This rapid melting caused floods such as the overflow of Lake Missoula and shaped the topography of the fertile Inland Empire of Eastern Washington.^[4] Further north, the Cordilleran is responsible for a large number of glacial landforms scattered across the west of Canada.^[5] The rate of thawing has also played a significant role in research surrounding early human migration into the American continents.

The rapid retreat of the Cordilleran ice sheet is a focus of study by glaciologists seeking to understand the difference in patterns of melting in marine-terminating glaciers, glaciers whose margin extends into open water without seafloor contact, and land-terminating glaciers, with a land or seafloor margin, as scientists believe the western marine-terminating margin retreated much faster than its southern, land-terminating front.^[6] This rapid retreat resulted in noticeably fewer glacial landforms in the west of the Cordilleran's maximum extent compared to the south and east, though the exact mechanisms behind this disparity are unknown. Some glacial landforms are still present though: the well-characterized landscape of coastal Washington State contains glacial troughs, some glacial lakes, and an extensive outwash plain.^[7] Many of the southern and eastern landforms fall near the northern reaches of the American Cordillera, the mountain ranges which geologists believe to be the region from which the Cordilleran first grew, and, after its sudden retreat and ultimate collapse, where it terminated.^[8]

The timing of the retreat of the Cordilleran bears significance not just to glaciologists, but to anthropologists interested in the migration of early humans into the Americas. In particular, the collapse of the western front of the Cordilleran ice sheet has been proposed as one route through which early humans could have migrated after crossing the Beringian Land Bridge during the Last Glacial Maximum.^[9] This serves as an alternative to the Ice Free Corridor previously posited to have allowed for migration amid the retreat of the eastern front of the Cordilleran ice sheet and the western front of the Laurentide ice sheet.^[10] The Ice Free Corridor is a subject of debate among anthropologists in recent years. Recent studies have provoked skepticism, with areas of discussion including the lack of evidence of sufficient flora in the area to support megafaunal migration,^[11] to radiometric dating placing the emergence of a corridor through the central Canadian Shield too late to account for the earliest known human sites south of the glaciers.^[12]

Sea levels during glaciation

Because of the weight of the ice, the mainland of northwest North America was so depressed that sea levels at the Last Glacial Maximum were over a hundred metres higher than they are today (measured by the level of bedrock).

However, on the western edge at the Haida Gwaii, the lower thickness of the ice sheet meant that sea levels were as much as 170 m (560 ft) lower than they are today, forming a lake in the deepest parts of the strait. This was because the much greater thickness of the center of the ice sheet served to push upwards areas at the edge of the continental shelf in a glacial forebulge. The effect of this during deglaciation was that sea levels on the edge of the ice sheet, which naturally deglaciated first, initially rose due to an increase in the volume of water, but later fell due to rebound after deglaciation. Some underwater features along the Pacific Northwest were exposed because of the lower sea levels, including Bowie Seamount west of Haida Gwaii which has been interpreted as an active volcanic island throughout the last ice age.

These effects are important because they have been used to explain how migrants to North America from Beringia were able to travel southward during the deglaciation process due purely to the exposure of submerged land between the mainland and numerous continental islands. They are also important for understanding the direction evolution has taken since the ice retreated.

Related Research Articles

The Wisconsin glaciation, also called the Wisconsin glacial episode, was the most recent glacial period of the North American ice sheet complex, peaking more than 20,000 years ago. This advance included the Cordilleran Ice Sheet, which nucleated in the northern North American Cordillera; the Innuitian ice sheet, which extended across the Canadian Arctic Archipelago; the Greenland ice sheet; and the massive Laurentide Ice Sheet, which covered the high latitudes of central and eastern North America. This advance was synchronous with global glaciation during the last glacial period, including the North American alpine glacier advance, known as the Pinedale glaciation. The Wisconsin glaciation extended from about 75,000 to 11,000 years ago, between the Sangamonian Stage and the current interglacial, the Holocene. The maximum ice extent occurred about 25,000–21,000 years ago during the last glacial maximum, also known as the Late Wisconsin in North America.

The Last Glacial Period (LGP), also known as the Last glacial cycle, occurred from the end of the Last Interglacial to the beginning of the Holocene, c. 115,000 – c. 11,700 years ago, and thus corresponds to most of the timespan of the Late Pleistocene.

Post-glacial rebound is the rise of land masses after the removal of the huge weight of ice sheets during the last glacial period, which had caused isostatic depression. Post-glacial rebound and isostatic depression are phases of glacial isostasy, the deformation of the Earth's crust in response to changes in ice mass distribution. The direct raising effects of post-glacial rebound are readily apparent in parts of Northern Eurasia, Northern America, Patagonia, and Antarctica. However, through the processes of ocean siphoning and continental levering, the effects of post-glacial rebound on sea level are felt globally far from the locations of current and former ice sheets.

<span class="mw-page-title-main">Last Glacial Maximum</span> Circa 24,000–16,000 BCE; most recent era when ice sheets were at their greatest extent

The Last Glacial Maximum (LGM), also referred to as the Last Glacial Coldest Period, was the most recent time during the Last Glacial Period where ice sheets were at their greatest extent 26,000 and 20,000 years ago. Ice sheets covered much of Northern North America, Northern Europe, and Asia and profoundly affected Earth's climate by causing a major expansion of deserts, along with a large drop in sea levels.

The Laurentide ice sheet (LIS) was a massive sheet of ice that covered millions of square miles, including most of Canada and a large portion of the Northern United States, multiple times during the Quaternary glaciation epochs, from 2.58 million years ago to the present.

Till plains are an extensive flat plain of glacial till that forms when a sheet of ice becomes detached from the main body of a glacier and melts in place, depositing the sediments it carried. Ground moraines are formed with melts out of the glacier in irregular heaps, forming rolling hills. Till plains are common in areas such as the Midwestern United States, due to multiple glaciation events that occurred in the Holocene epoch. During this period, the Laurentide Ice Sheet advanced and retreated during the Pleistocene epoch. Till plains formed by the Wisconsin glaciation cover much of the Midwest, including North Dakota, South Dakota, Indiana, Minnesota, Wisconsin, Iowa, Illinois, and northern Ohio.

<span class="mw-page-title-main">Glacial landform</span> Landform created by the action of glaciers

Glacial landforms are landforms created by the action of glaciers. Most of today's glacial landforms were created by the movement of large ice sheets during the Quaternary glaciations. Some areas, like Fennoscandia and the southern Andes, have extensive occurrences of glacial landforms; other areas, such as the Sahara, display rare and very old fossil glacial landforms.

The Desert of Maine is a natural curiosity and privately owned tourist attraction whose main feature is a 20-acre (8.1 ha) expanse of barren glacial sand in the town of Freeport, Maine, United States. The area was de‑vegetated by poor farming practices in the 19th century.

The Quaternary glaciation, also known as the Pleistocene glaciation, is an alternating series of glacial and interglacial periods during the Quaternary period that began 2.58 Ma and is ongoing. Although geologists describe this entire period up to the present as an "ice age", in popular culture this term usually refers to the most recent glacial period, or to the Pleistocene epoch in general. Since Earth still has polar ice sheets, geologists consider the Quaternary glaciation to be ongoing, though currently in an interglacial period.

The Holocene glacial retreat is a geographical phenomenon that involved the global retreat of glaciers (deglaciation) that previously had advanced during the Last Glacial Maximum. Ice sheet retreat initiated ca. 19,000 years ago and accelerated after ca. 15,000 years ago. The Holocene, starting with abrupt warming 11,700 years ago, resulted in rapid melting of the remaining ice sheets of North America and Europe.

A tunnel valley is a U-shaped valley originally cut under the glacial ice near the margin of continental ice sheets such as that now covering Antarctica and formerly covering portions of all continents during past glacial ages. They can be as long as 100 km (62 mi), 4 km (2.5 mi) wide, and 400 m (1,300 ft) deep.

The neoglaciation describes the documented cooling trend in the Earth's climate during the Holocene, following the retreat of the Wisconsin glaciation, the most recent glacial period. Neoglaciation has followed the hypsithermal or Holocene Climatic Optimum, the warmest point in the Earth's climate during the current interglacial stage, excluding the global warming-induced temperature increase starting in the 20th century. The neoglaciation has no well-marked universal beginning: local conditions and ecological inertia affected the onset of detectably cooler conditions.

Lake Bassano was a proglacial lake that formed in the Late Pleistocene during the deglaciation of south-central Alberta by the impoundment of a re-established drainage system and addition of glacial meltwater. It is associated with the development of through-flowing drainage within the Red Deer River basin in particular, and the South Saskatchewan drainage network in general. Approximately 7,500 square kilometres (2,900 sq mi) of the Bassano basin is covered with lacustrine sediments. These sediments are bordered by the topographically higher Buffalo Lake Moraine to the west, the Suffield Moraine to the east and the Lethbridge Moraine to the south.

<span class="mw-page-title-main">Weichselian glaciation</span> Last glacial period and its associated glaciation in northern parts of Europe

The Weichselian glaciation is the regional name for the Last Glacial Period in the northern parts of Europe. In the Alpine region it corresponds to the Würm glaciation. It was characterized by a large ice sheet that spread out from the Scandinavian Mountains and extended as far as the east coast of Schleswig-Holstein, northern Poland and Northwest Russia. This glaciation is also known as the Weichselian ice age, Vistulian glaciation, Weichsel or, less commonly, the Weichsel glaciation, Weichselian cold period (Weichsel-Kaltzeit), Weichselian glacial (Weichsel-Glazial), Weichselian Stage or, rarely, the Weichselian complex (Weichsel-Komplex).

Deglaciation is the transition from full glacial conditions during ice ages, to warm interglacials, characterized by global warming and sea level rise due to change in continental ice volume. Thus, it refers to the retreat of a glacier, an ice sheet or frozen surface layer, and the resulting exposure of the Earth's surface. The decline of the cryosphere due to ablation can occur on any scale from global to localized to a particular glacier. After the Last Glacial Maximum, the last deglaciation begun, which lasted until the early Holocene. Around much of Earth, deglaciation during the last 100 years has been accelerating as a result of climate change, partly brought on by anthropogenic changes to greenhouse gases.

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References

1 2 3 Martin Margold; Krister N. Jansson; Johan Kleman; Arjen P. Stroeven; John J. Clague (18 February 2013). "Retreat pattern of the Cordilleran Ice Sheet in central British Columbia at the end of the last glaciation reconstructed from glacial meltwater landforms". Boreas. 42 (4). Wiley Online Library: 830–847. doi:10.1111/bor.12007.
↑ Dyke, Arthur S. (2004), "An outline of North American deglaciation with emphasis on central and northern Canada", Quaternary Glaciations-Extent and Chronology - Part II: North America, Developments in Quaternary Sciences, vol. 2, Elsevier, pp. 373–424, doi:10.1016/s1571-0866(04)80209-4, ISBN 978-0-444-51592-6 , retrieved 2024-04-01
↑ Darvill, C. M.; Menounos, B.; Goehring, B. M.; Lesnek, A. J. (2022-05-28). "Cordilleran Ice Sheet Stability During the Last Deglaciation". Geophysical Research Letters. 49 (10). Bibcode:2022GeoRL..4997191D. doi: 10.1029/2021GL097191 . ISSN 0094-8276.
↑ Topinka, L (2002). "The Cordilleran Ice Sheet and Missoula Floods". United States Geological Survey.
↑ Arnold, H.; Ferbey, T.; Hickin, A. S. (2016). "Ice-flow indicator compilation, British Columbia and Yukon". ostrnrcan-dostrncan.canada.ca. doi: 10.4095/298865 . Retrieved 2024-03-08.
↑ Lesnek, Alia J.; Briner, Jason P.; Baichtal, James F.; Lyles, Alex S. (July 2020). "New constraints on the last deglaciation of the Cordilleran Ice Sheet in coastal Southeast Alaska". Quaternary Research. 96: 140–160. Bibcode:2020QuRes..96..140L. doi:10.1017/qua.2020.32. ISSN 0033-5894.
↑ Booth, Derek B.; Troost, Kathy Goetz; Clague, John J.; Waitt, Richard B. (2003), "The Cordilleran Ice Sheet", The Quaternary Period in the United States, vol. 1, Elsevier, pp. 17–43, Bibcode:2003DevQS...1...17B, doi:10.1016/s1571-0866(03)01002-9, ISBN 978-0-444-51470-7 , retrieved 2024-04-01
↑ Dulfer, Helen E.; Margold, Martin (2021-12-01). "Glacial geomorphology of the central sector of the Cordilleran Ice Sheet, Northern British Columbia, Canada". Journal of Maps. 17 (2): 413–427. Bibcode:2021JMaps..17..413D. doi: 10.1080/17445647.2021.1937729 . ISSN 1744-5647.
↑ Lesnek, Alia J.; Briner, Jason P.; Lindqvist, Charlotte; Baichtal, James F.; Heaton, Timothy H. (2018-05-04). "Deglaciation of the Pacific coastal corridor directly preceded the human colonization of the Americas". Science Advances. 4 (5): eaar5040. Bibcode:2018SciA....4.5040L. doi:10.1126/sciadv.aar5040. ISSN 2375-2548. PMC 5976267 . PMID 29854947.
↑ Flannery, Tim F. (2002). The eternal frontier: an ecological history of North America and its peoples (2. [print.] ed.). New York, NY: Grove Press. ISBN 978-0-8021-3888-0.
↑ Pedersen, Mikkel W.; Ruter, Anthony; Schweger, Charles; Friebe, Harvey; Staff, Richard A.; Kjeldsen, Kristian K.; Mendoza, Marie L. Z.; Beaudoin, Alwynne B.; Zutter, Cynthia; Larsen, Nicolaj K.; Potter, Ben A.; Nielsen, Rasmus; Rainville, Rebecca A.; Orlando, Ludovic; Meltzer, David J. (September 2016). "Postglacial viability and colonization in North America's ice-free corridor". Nature. 537 (7618): 45–49. Bibcode:2016Natur.537...45P. doi:10.1038/nature19085. ISSN 1476-4687. PMID 27509852.
↑ Clark, Jorie; Carlson, Anders E.; Reyes, Alberto V.; Carlson, Elizabeth C. B.; Guillaume, Louise; Milne, Glenn A.; Tarasov, Lev; Caffee, Marc; Wilcken, Klaus; Rood, Dylan H. (2022-04-05). "The age of the opening of the Ice-Free Corridor and implications for the peopling of the Americas". Proceedings of the National Academy of Sciences. 119 (14): e2118558119. Bibcode:2022PNAS..11918558C. doi: 10.1073/pnas.2118558119 . ISSN 0027-8424. PMC 9168949 . PMID 35312340.

Hidy, A. J., Gosse, J. C., Froese, D. G., Bond, J. D., and Rood, D. H. (2013). A latest Pliocene age for the earliest and most extensive Cordilleran Ice Sheet in northwestern Canada. Quaternary Science Reviews 61:77-84.
Gwaii Haanas National Park Reserve and Haida Heritage Site ^{[ permanent dead link ‍]}
Clarke, T.E., D.B. Levin, D.H. Kavanaugh and T.E. Reimchen. 2001. Rapid Evolution in the Nebria Gregaria Group (Coleoptera: Carabidae) and the Paleogeography of the Queen Charlotte Islands. Evolution 51:1408–1418
Brown, A. S., and H. Nasmith. 1962. The glaciation of the Queen Charlotte Islands. Canadian Field-Naturalist 76:209–219.
Byun, S. A., B. F. Koop, and T. E. Reimchen. 1997. North American black bear mtDNA phylogeography: implications for morphology and the Haida Gwaii glacial refugium controversy. Evolution 51:1647–1653.
Richard B. Waitt, Jr., and Robert M. Thorson, 1983. The Cordilleran Ice Sheet in Washington, Idaho, and Montana. IN: H.E. Wright, Jr., (ed.), 1983, Late-Quaternary Environments of the United States, Volume 1: The Late Pleistocene (Stephen C. Porter (ed.)): University of Minnesota Press, 407p., Chapter 3, p.53-70. Abstract
Holder, K., Montgomerie, R., and V.L. Friesen. 1999. A test of the glacial refugium hypothesis using patterns of mitochondrial and nuclear DNA sequence variation in the rock ptarmingan (Lagopus mutus). Evolution 53(6):1936–1950.
Warner, B.G., Mathewes, R.W., and J.J. Clague. 1982. Ice-free conditions on the Queen Charlotte Islands, British Columbia, at the height of late Wisconsin glaciation. Science 218(4573):675–6770

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[2013-central-1] 1 2 3 Martin Margold; Krister N. Jansson; Johan Kleman; Arjen P. Stroeven; John J. Clague (18 February 2013). "Retreat pattern of the Cordilleran Ice Sheet in central British Columbia at the end of the last glaciation reconstructed from glacial meltwater landforms". Boreas. 42 (4). Wiley Online Library: 830–847. doi:10.1111/bor.12007.

[2] Dyke, Arthur S. (2004), "An outline of North American deglaciation with emphasis on central and northern Canada", Quaternary Glaciations-Extent and Chronology - Part II: North America, Developments in Quaternary Sciences, vol. 2, Elsevier, pp. 373–424, doi:10.1016/s1571-0866(04)80209-4, ISBN 978-0-444-51592-6 , retrieved 2024-04-01

[3] Darvill, C. M.; Menounos, B.; Goehring, B. M.; Lesnek, A. J. (2022-05-28). "Cordilleran Ice Sheet Stability During the Last Deglaciation". Geophysical Research Letters. 49 (10). Bibcode:2022GeoRL..4997191D. doi: 10.1029/2021GL097191 . ISSN 0094-8276.

[4] Topinka, L (2002). "The Cordilleran Ice Sheet and Missoula Floods". United States Geological Survey.

[5] Arnold, H.; Ferbey, T.; Hickin, A. S. (2016). "Ice-flow indicator compilation, British Columbia and Yukon". ostrnrcan-dostrncan.canada.ca. doi: 10.4095/298865 . Retrieved 2024-03-08.

[6] Lesnek, Alia J.; Briner, Jason P.; Baichtal, James F.; Lyles, Alex S. (July 2020). "New constraints on the last deglaciation of the Cordilleran Ice Sheet in coastal Southeast Alaska". Quaternary Research. 96: 140–160. Bibcode:2020QuRes..96..140L. doi:10.1017/qua.2020.32. ISSN 0033-5894.

[7] Booth, Derek B.; Troost, Kathy Goetz; Clague, John J.; Waitt, Richard B. (2003), "The Cordilleran Ice Sheet", The Quaternary Period in the United States, vol. 1, Elsevier, pp. 17–43, Bibcode:2003DevQS...1...17B, doi:10.1016/s1571-0866(03)01002-9, ISBN 978-0-444-51470-7 , retrieved 2024-04-01

[:0-8] Dulfer, Helen E.; Margold, Martin (2021-12-01). "Glacial geomorphology of the central sector of the Cordilleran Ice Sheet, Northern British Columbia, Canada". Journal of Maps. 17 (2): 413–427. Bibcode:2021JMaps..17..413D. doi: 10.1080/17445647.2021.1937729 . ISSN 1744-5647.

[9] Lesnek, Alia J.; Briner, Jason P.; Lindqvist, Charlotte; Baichtal, James F.; Heaton, Timothy H. (2018-05-04). "Deglaciation of the Pacific coastal corridor directly preceded the human colonization of the Americas". Science Advances. 4 (5): eaar5040. Bibcode:2018SciA....4.5040L. doi:10.1126/sciadv.aar5040. ISSN 2375-2548. PMC 5976267 . PMID 29854947.

[10] Flannery, Tim F. (2002). The eternal frontier: an ecological history of North America and its peoples (2. [print.] ed.). New York, NY: Grove Press. ISBN 978-0-8021-3888-0.

[11] Pedersen, Mikkel W.; Ruter, Anthony; Schweger, Charles; Friebe, Harvey; Staff, Richard A.; Kjeldsen, Kristian K.; Mendoza, Marie L. Z.; Beaudoin, Alwynne B.; Zutter, Cynthia; Larsen, Nicolaj K.; Potter, Ben A.; Nielsen, Rasmus; Rainville, Rebecca A.; Orlando, Ludovic; Meltzer, David J. (September 2016). "Postglacial viability and colonization in North America's ice-free corridor". Nature. 537 (7618): 45–49. Bibcode:2016Natur.537...45P. doi:10.1038/nature19085. ISSN 1476-4687. PMID 27509852.

[12] Clark, Jorie; Carlson, Anders E.; Reyes, Alberto V.; Carlson, Elizabeth C. B.; Guillaume, Louise; Milne, Glenn A.; Tarasov, Lev; Caffee, Marc; Wilcken, Klaus; Rood, Dylan H. (2022-04-05). "The age of the opening of the Ice-Free Corridor and implications for the peopling of the Americas". Proceedings of the National Academy of Sciences. 119 (14): e2118558119. Bibcode:2022PNAS..11918558C. doi: 10.1073/pnas.2118558119 . ISSN 0027-8424. PMC 9168949 . PMID 35312340.

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