DUST EMISSION POTENTIAL OF MISSOURI RIVER SAND BARS DEPOSITED BY THE 2011 FLOOD

The thick Peoria loess that mantles the southern bluffs along the 59-mile segment of the Missouri National Recreational River is assumed to be derived from wind erosion of expansive braid bars in glacial melt water streams of the late Pleistocene. Dust from sand bars emplaced by the 2011 flood can be used as a proxy to estimate the environmental conditions necessary for the origin of the loess. A PI-SWERL (Portable in situ Wind Erosion Lab) was used to measure the potential of three different sand bars near Vermillion, SD to emit dust. The threshold velocity for sand and dust entrainment along a transect on each bar was measured. Surface samples were collected and analyzed for grain size and composition. Each bar was mapped using GIS by the type of surface including fluvially deposited sand and gravel with occasional silt rich zones, eolian sand dunes and wind ripples, and gravel lags. Dust emission potential was assigned to each type of surface. Fluvial sediments, especially those with higher silt contents, were the highest dust emitters whereas eolian sands were lower dust emitters. Rapid eolian and fluvial erosion of the sand bars make bars short-lived dust sources. Even though suspended load concentrations and frequency of bar generation are greatly reduced from late Pleistocene conditions, dust emission measurements from flood-generated bars can provide a first approximation for volumes of dust produced by sand bars.