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Nivation Landforms in the Western Great Basin and Their Paleoclimatic Significance
- John C. Dohrenwend
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- Journal:
- Quaternary Research / Volume 22 / Issue 3 / November 1984
- Published online by Cambridge University Press:
- 20 January 2017, pp. 275-288
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More than 10,000 nivation landforms occur in the higher mountain ranges of the western Great Basin. They range from small, subtle hollows with head scarps a few meters high and a few tens of meters long to broad, clearly defined terraces as much as 220 m wide bounded by bold, steeply sloping head scarps as much as 30 m high and 1600 m long. Distribution of these nivation hollows is strongly influenced by elevation, slope orientation, local relief, and substrate lithology. About 95% occur between 2200 and 3000 m elevation, and nearly 80% are situated on north-northwest-to east-northeast-facing slopes. They occur mainly in areas of moderately sloping terrain and moderate local relief, and they are preferentially developed on relatively incompetent substrates including terrigenous sedimentary deposits, volcanic and metavolcanic rocks of intermediate composition, and deeply weathered granitoid rocks. Nearly all of these nivation hollows are relict. They are most abundant near areas of late Pleistocene glaciation but rarely occur within such areas. Most are veneered with colluvium and are well vegetated, and many hollows in the Mono Basin area are veneered with volcanic ash at least 700 yr old. Distribution of nivation hollows suggests that (1) the full-glacial nivation threshold altitude (NTA) rose from north to south at 190 m per degree of latitude, subparallel to, and approximately 740 m lower than, the full-glacial equilibrium-line altitude (ELA) and about 1370 m lower than the estimated modern ELA; (2) the difference between the full-glacial and modern ELAs indicates an approximate 7°C full-glacial mean-annual-temperature depression throughout the Great Basin; and (3) the full-glacial mean annual temperature at the NTA is estimated to have been approximately 0° to 1°C, assuming little change in accumulation-season precipitation.
Influence of Late Quaternary Climatic Changes on Geomorphic and Pedogenic Processes on a Desert Piedmont, Eastern Mojave Desert, California
- Stephen G. Wells, Leslie D. McFadden, John C. Dohrenwend
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- Journal:
- Quaternary Research / Volume 27 / Issue 2 / March 1987
- Published online by Cambridge University Press:
- 20 January 2017, pp. 130-146
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Radiocarbon dating of late Quaternary deposits and shorelines of Lake Mojave and cation-ratio numerical age dating of stone pavements (Dorn, 1984) on the adjacent Soda Mountains piedmont provide age constraints for alluvial and eolian deposits. These deposits are associated with climatically controlled stands of Lake Mojave during the past 15,000 yr. Six alluvial fan units and three eolian stratigraphic units were assigned ages based on field relations with dated shorelines and piedmont surfaces, as well as on soil-geomorphic data. All but one of these stratigraphic units were deposited in response to time-transgressive climatic changes beginning approximately 10,000 yr ago. Increased eolian flux rates occurred in response to the lowering of Lake Mojave and a consequent increase in fine-sediment availability. Increased rates of deposition of eolian fines and associated salts influenced pedogenesis, stone-pavement development, and runoff-infiltration relations by (1) enhancing mechanical weathering of fan surfaces and hillslopes and (2) forming clay- and silt-rich surface horizons which decrease infiltration. Changes in alluvial-fan source areas from hillslopes to piedmonts during the Holocene reflect runoff reduction on hillslopes caused by colluvial mantle development and runoff enhancement on piedmonts caused by the development of less-permeable soils. Inferred increased in early to middle Holocene monsoonal activity resulted in high-magnitude paleo-sheetflood events on older fan pavements; this runoff triggered piedmont dissection which, in turn, caused increased sediment availability along channel walls. Thus, runoff-infiltration changes during the late Quaternary have occurred in response to eolian deposition of fines, pedogenesis, increased sheetflood activity in the Holocene, and vegetational changes which are related to many complicated linkages among climatic change, lake fluctuations, and eolian, hillslope, and alluvial-fan processes.
Contributors
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- By Avishek Adhikari, Susanne E. Ahmari, Anne Marie Albano, Carlos Blanco, Desiree K. Caban, Jonathan S. Comer, Jeremy D. Coplan, Ana Alicia De La Cruz, Emily R. Doherty, Bruce Dohrenwend, Amit Etkin, Brian A. Fallon, Michael B. First, Abby J. Fyer, Angela Ghesquiere, Jay A. Gingrich, Robert A. Glick, Joshua A. Gordon, Ethan E. Gorenstein, Marco A. Grados, James P. Hambrick, James Hanks, Kelli Jane K. Harding, Richard G. Heimberg, Rene Hen, Devon E. Hinton, Myron A. Hofer, Matthew J. Kaplowitz, Sharaf S. Khan, Donald F. Klein, Karestan C. Koenen, E. David Leonardo, Roberto Lewis-Fernández, Jeffrey A. Lieberman, Michael R. Liebowitz, Sarah H. Lisanby, Antonio Mantovani, John C. Markowitz, Patrick J. McGrath, Caitlin McOmish, Jeffrey M. Miller, Jan Mohlman, Elizabeth Sagurton Mulhare, Philip R. Muskin, Navin Arun Natarajan, Yuval Neria, Nicole R. Nugent, Mayumi Okuda, Mark Olfson, Laszlo A. Papp, Sapana R. Patel, Anthony Pinto, Kristin Pontoski, Jesse W. Richardson-Jones, Carolyn I. Rodriguez, Steven P. Roose, Moira A. Rynn, Franklin Schneier, M. Katherine Shear, Ranjeeb Shrestha, Helen Blair Simpson, Smit S. Sinha, Natalia Skritskaya, Jami Socha, Eun Jung Suh, Gregory M. Sullivan, Anthony J. Tranguch, Hilary B. Vidair, Tor D. Wager, Myrna M Weissman, Noelia V. Weisstaub
- Edited by Helen Blair Simpson, Columbia University, New York, Yuval Neria, Columbia University, New York, Roberto Lewis-Fernández, Columbia University, New York, Franklin Schneier, Columbia University, New York
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- Book:
- Anxiety Disorders
- Published online:
- 10 November 2010
- Print publication:
- 26 August 2010, pp vii-xii
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