Cordilleran ice sheet
| Cordilleran Ice Sheet | |
|---|---|
 Southern edge of the ice sheet. It extended north along the Pacific coast and covered the Alaska Peninsula. | |
| Type | continental |
| Location | Canadian Shield |
| Lowest elevation | Sea level |
| Terminus | West – Pacific Ocean East – Great Plains South – 40 degrees north latitude |
| Status | List of glaciers in Canada and List of glaciers in the United States |
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
The ice sheet covered up to 2,500,000 km2 (970,000 sq mi) at the Last Glacial Maximum 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
Thawing
Unlike the Laurentide Ice Sheet, which may have taken as many as eleven thousand years to fully melt,
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.
See also
References
- ^ Fulton, R. J. & Prest, V. K. (1987). Introduction: The Laurentide Ice Sheet and its Significance. Géographie physique et Quaternaire, 41 (2), 181–186
- ISBN 978-0-444-51592-6, retrieved 2024-04-01
- ISSN 0094-8276.
- ^ Topinka, L (2002). "The Cordilleran Ice Sheet and Missoula Floods". United States Geological Survey.
- doi:10.4095/298865. Retrieved 2024-03-08.
- ISSN 0033-5894.
- ISBN 978-0-444-51470-7, retrieved 2024-04-01
- ISSN 1744-5647.
- PMID 29854947.
- ISBN 978-0-8021-3888-0.
- PMID 27509852.
- 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. [1]
- 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. [2]
- 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 [3]