| Even Longer Records Changes in Great Plains Landcover Forman, S.L. and Oglesby, R. Complete Scientific Reference Summary: The semi-arid Great Plains is covered by >100,000 km2 of eolian (wind blown) deposits which contain evidence for episodes of dune formation, or reactivation of old dunes, over the past 10,000 years. The region of multiple sand dunes and eolian deposits across the central United States (figure on this page) is currently stabilized by vegetation. However, analyses of sediments within sand dunes (stratigraphic records) and the shapes of the dunes (geomorphic records) provide information about multiple past droughts, which resulted in the removal of vegetation, and the movement and accumulation of eolian sand. Accumulations of eolian sediment and formation of dunes occurs when there is adequate sediment supply, when winds exceed the speed needed to move particles of sand, and when there is a lack of stabilizing vegetation or landforms. On the Great Plains, there is adequate sediment supply. Wind strength is already sufficient in much of the Great Plains to move silt and sand, and create widespread active dunes. When a decrease in moisture results in a reduction of vegetation cover below a threshold (~30% decrease in rainfall), dunes can once again become active.
The combination of integrated geomorphic and stratigraphic studies and advances
in dating techniques has lead to an enhanced understanding of the timing and
location of Holocene (the last 10,000 years) eolian activity on the Great Plains.
The figure to the right (click here or on the figure for a larger version) , from the work of Forman and Munyikwa, shows the spatial distribution and extent of stabilized dune fields (in brown) in the North American Great Plains. Superimposed on this map are 15 time series for the last 10,000 years with evidence for episodes of dry and moist conditions (LS denotes landscape stability, DR denotes dune reactivation. HW denotes high water level, LL denotes low water level). Back to... Even Longer Records. |
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