A RECORD OF DROUGHT AND DUNE ACTIVATION ON THE SNAKE RIVER PLAIN IN SOUTHEASTERN IDAHO: RESULTS FROM TESTING A HYPOTHESIS REGARDING THE POTENTIAL BONNEVILLE-FLOOD SOURCE OF THE DUNE SAND

A prominent, narrow ridge of now mostly relict sand dunes extends for 155 kilometers along the Snake River Plain in a northeast-southwest orientation between Idaho Falls and Rupert, Idaho. Dune forms range from nondescript low dunes and sand sheets to 10-m tall parabolic dunes and lower relief hairpin parabolic dunes. Paleowind directions determined from dune forms and sedimentary structures are distinctly from the southwest and are the same as the dominant wind direction today.

Research goals were to test Scott's (1982) hypothesis that the source sediment for these dunes came from the Bonneville flood and therefore the oldest deposits should date to ~18 ka. In order to test this hypothesis the dunes were mapped using ArcGIS and potential sample sites were identified. In the field, the sedimentology and soil stratigraphy was described from dune exposures and hand augered cores. Twelve samples were collected from eight different sand dunes and were analyzed for grain size, organic content, magnetic susceptibility, elemental analysis, and then processed for optically stimulated luminescence (OSL) dating. Additionally, a sample was collect from Bonneville flood sands in order to provide greater age control on the timing of the drainage of Lake Bonneville.

Preliminary OSL ages from the dunes are younger then the Bonneville flood but may indicate a record of past climate change on the Snake River Plain. The OSL ages from dune sand bracketed by paleosols provides the time periods of dune activation. Based on preliminary results, this dune field was actively migrating around 4400 yr, 2200 yr, 1900-1500 yr, 700 yr, 220-250 yr and as recently as 70-90 years ago. Based on these results there have been several cycles of dune activation and stability on the Snake River Plain signifying several periods of drought. Funding for this undergraduate research project was provided by the URCO foundation at Utah State University.