Formation of linear and parabolic dunes on the eastern Snake River Plain, Idaho in the nineteenth century

Geomorphic and stratigraphic evidence show periods of distinct hydrologic excess and deficit sometime in the past 500 years on the eastern Snake River Plain. Natural exposures at the current shore of Mud Lake contain a lacustrine silty sand beneath eolian sands; the latter deposit is expressed at the surface as hairpin parabolic and linear dunes. These dunes can be traced into and across lakes, a clear sign of recent aridity. Two shallow-water gastropods and two wood fragments from the lacustrine silty sand yield the respective AMS 14C ages of ca. 705 and 988 year BP, and 195 and 305 year BP. The offset in ages indicates a lake hard-water effect of aquatic gastropods, with the wood ages providing the closest age constraint. Optically stimulated luminescence single aliquot regeneration ages of 150±30 and 120±20 year BP on quartz grains from the overlying eolian sands further constrains a drop in lake level and subsequent aridity to the 19th century. This lacustrine–dune sequence is probably the geomorphic expression of a distinct wet period followed by a severe drought between AD 1845 and 1856, which has been documented in the dendroclimatic records for the Rocky Mountains and the western Great Plains. Lake fluctuations and dune formation is associated with greater subdecadal variability in spring precipitation, than recorded in the past 100 years.