DROUGHT AND DUNE ACTIVITY IN THE IDAHO FALLS DUNE FIELD, 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 and may originate from sediment derived from the Bonneville Flood (Scott, 1982), which emptied into the Snake River valley near the downstream-upwind end of the dune field. 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 a record of previous dune activations. The stratigraphy, sedimentology and chronology of the dunes was investigated to determine if they recorded a coherent response to past aridity. In the field, the sedimentology and soil stratigraphy was described from dune exposures and hand augered cores. Stratigraphic samples were analyzed for grain size, organic content, magnetic susceptibility and elemental analysis. Stacked eolian deposits were dated with optically stimulated luminescence (OSL) dating.

The OSL ages from dune sand bracketed by paleosols indicate multiple periods of dune activation during the late Holocene. Results indicate that dunes were destabilized around 3000 yr (n=1), 2000 yr (n=2), 1200 yr (n=1), 700 yr (n=1), and as recently as 80-140 years ago (n=4). Current research is focusing on the description of more exposures and cores in order to develop a robust record of aridity and dune activity for the eastern Snake River Plain. Results will be compared to other dune records within the region (e.g Forman and Pierson, 2003) and regional tree ring and paleoclimate data.