Bull Lake glaciation

The Bull Lake glaciation is the name of a glacial period in North America that is part of the Quaternary Ice Age. The Bull Lake glaciation began about 200,000 years ago and ended about 130,000 years ago, and was concurrent with the Illinoian Stage of the Quaternary Ice Age.[1] There is disagreement over these time frames, however, and further research is necessary.[2]

This glacial period was identified by geologist Eliot Blackwelder.[3] It draws its name from Bull Lake in Wyoming in the United States, where well-preserved moraines from this glacial period were first described. Although Blackwelder originally believed the Bull Lake glaciation occurred during the early Wisconsin Glaciation (the last major advance of glaciers in the North America), new data generated and described by geologist Gerald M. Richmond in the 1940s and 1960s more accurately dated the glacial period to the Illinoian Stage.[4]

The Bull Lake glaciation was a local glaciation. It did not cover the entire North American continent but rather just the eastern slopes of the southern Rocky Mountains. Generally speaking, it extended from northwestern Montana south to the San Juan Mountains in Colorado.[2] The Bull Lake glaciation has three periods—Early, Middle and Late—punctuated by periods of relative warmth (during which glaciers retreated).[5]

The Bull Lake glaciation is generally considered to be much less extensive than the preceding glaciations.[2] However, the reach of the glaciers varied from place to place, extending further in some areas than others.[2] Bull Lake moraines remain relatively undisturbed, indicating that glacial periods which came later were only about 90 percent as extensive as the Bull Lake glaciation.[2]

The Bull Lake Glaciation was followed by a warm interglacial period that lasted about 60,000 years. The Pinedale Glaciation, another local glacial period, occurred after this warm period.

References
  1. Fullerton, David S.; Colton, Roger B.; and Bush, Charles A. "Limits of Mountain and Continental Glaciations in Northern Montana and North-Western North Dakota, U.S.A." In Quaternary Glaciations: Extent and Chronology. Part II: North America. Jim Rose, ed. San Diego, Calif.: Elsevier, 2004.
  2. Pierce, Kenneth L. "Pleistocene Glaciations of the Rocky Mountains." Archived 2010-05-30 at the Wayback Machine Development in Quaternary Science. 1 (2003).
  3. Kelsey, Joe. Climbing and Hiking in the Wind River Mountains. Evergreen, Colo.: Chockstone Press, 1994; Balckwelder, Eliot. "Post-Cretaceous History of the Mountains of Central Western Wyoming." Journal of Geology. 23 (1915): 214-15.
  4. Richmond, Gerald M. Geology of the Northwest End of the Wind River Mountains, Sublette County, Wyoming. U.S. Geological Survey O1 map 31. 1945; Richmond, Gerald M. "Three Pre–Bull Lake Tills in the Wind River Mountains, Wyoming: A Reinterpretation." U.S. Geological Survey Professional Paper 501-D. 1964; Richmond, Gerald M. "Glaciation of the Rocky Mountains." In The Quaternary of the United States. H.E. Wright, Jr., and D.G. Frey, eds. Princeton, N.J.: Princeton University Press, 1965; Pierce, Kenneth L.; Obradovich, John D.; and Friedman, Irving. "Obsidian Hydration Dating and Correlation of Bull Lake and Pinedale Glaciations Near West Yellowstone, Montana." GSA Bulletin. 87:5 (May 1976): 703-710.
  5. Elias, Scott. The Ice-Age History of National Parks in the Rocky Mountains. Washington, D.C.: Smithsonian Institution, 1996; Richmond, Gerald M. "Appraisal of the Future Climate of the Holocene in the Rocky Mountains." Quaternary Research. 2:3 (November 1972): 315-322.
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