DUNE ACTIVITY IN THE IDAHO FALLS DUNE FIELD ON THE SNAKE RIVER PLAIN, SOUTHEASTERN IDAHO

The eastern Snake River Plain contains a prominent, narrow dune field that extends for 155 kilometers along a northeast-southwest orientation between Idaho Falls and Rupert, Idaho. This dune field sits on a Pleistocene braidbelt of the Snake River. Dune forms are mostly relict and range from non-descript 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 indicate winds from the southwest, the same as the dominant wind direction today.

Sediment exposures in the dunes reveal buried soils and records of previous dune mobilization and sand deposition. In the field, the sedimentology and soil stratigraphy was described from outcrop exposures and hand augered cores. Stratigraphic samples were analyzed for grain size, organic content, magnetic susceptibility and elemental analysis. Dunes and stacked eolian deposits were dated with optically stimulated luminescence (OSL) dating.

The OSL ages from dune sand bracketed by paleosols provides the time periods of dune activation. Based on these ages and stratigraphic relationships to bracketing soil horizons, sand dunes were active ~6 ka, ~3 ka, ~2.5 ka ~2 ka, ~1.7 ka, ~1.0 ka, ~800 yr, ~600-700 yr, ~500 yr, ~350 yr and as recently as 80-140 years ago. Based on these results there have been several cycles of dune activation and stability on the southeastern Snake River Plain signifying several periods of drought.