INSIGHTS INTO RECENT ACTIVITY IN THE ST. ANTHONY DUNE FIELD, NORTHEASTERN SNAKE RIVER PLAIN, IDAHO
HOOVER, Rachael H., School of Earth & Environmental Sciences, Washington State University, Webster Physical Science Building 1228, Pullman, WA 99164, GAYLORD, David R., School of Earth & Environmental Sciences, Washington State University, PO Box 642812, Pullman, WA 99164-2812, RUPP, Richard A., Crop and Soil Sciences, Washington State University, Pullman, WA 99163 and PHILLIPS, William M., Idaho Geological Survey, University of Idaho, 875 Perimeter Dr MS 3014, Moscow, ID 83844-3014, hooverrh@gmail.com
The NE dune complex of the St. Anthony Dune Field, Idaho consists of ~20 km2of barchanoid ridge, barchan, and parabolic dunes. Mapping crestal positions and areas of active, partially stabilized and stabilized dunes using archival air photos and GIS reveals changes in the rates and timing of dune migration during a 57-year period. From 1954-2011 dunes on the northeastern (downwind) margin of the dune complex migrated at an average rate of 4.1 m/yr; concurrently, dunes on the upwind margin migrated at an average rate of 7.5 m/yr and dunes in the interior migrated at an average rate 2.2 m/yr. Differences between exterior and interior dune migration rates are explained by increased dune heights that vary inversely with migration rate. Differences between upwind and downwind margin dune migration rates are attributed primarily to changing surface roughness. Faster migration rates on the upwind margin are attributed to enhanced dune migration across relatively smooth, unvegetated dunes and interdune basalt. Slower migration rates on the downwind margin are attributed to the influence of relatively rough, shrub-dominated vegetation on sand transport. Despite differences in migration rates, the estimated volume and spatial extent of dunes in the NE complex since 1954 have remained essentially constant; an outcome attributed to interactions among climate, vegetation and the surrounding topography.
Preliminary textural analyses suggest downwind particle fining even as secondary winds extensively modify active dune morphologies. Sparse grasses dominate active to partially stabilized dunes whereas 2-6 meter high shrubs dominate stabilized dunes. Interdune areas are dominated by basalt flow rock that promotes sediment bypass rather than deposition. Regional meteorological data for the past 57 years reveal that persistently arid conditions have been interrupted by year-long episodes of increased and decreased moisture. The absence of significant change in either the volume or spatial distribution of active to partially stabilized dunes in their present topographic setting suggests they may be in balance with a changing climate, vegetation and wind patterns. However, it remains to be seen whether this potentially tenuous balance will be maintained with increasingly extreme and perhaps lengthy episodes of aridity.
