MAPPING PLAYA EVAPORITE MINERALS WITH AVIRIS DATA - A 1ST REPORT FROMDEATH-VALLEY, CALIFORNIA

Efflorescent salt crusts in Death Valley, California, were mapped by u sing Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data and a recently developed least-squares spectral band-fitting algorithm. Ei ght different saline minerals were remotely identified, including thre e borates, hydroboracite, pinnoite, and rivadavite, that have not been previously reported from the Death Valley efflorescent crusts. The th ree borates are locally important phases in the crusts, and at least o ne Of the minerals, rivadavite, appears to be forming directly from br ine. Borates and other evaporite minerals provide a basis for making r emote chemical measurements of desert hydrologic systems. For example, in the Eagle Borax Spring area, the AVIRIS mineral maps pointed to el evated magnesium and boron levels in the ground waters, and to the act ion of chemical divides causing subsurface fractionation of calcium. M any other chemical aspects of playa brines should have an expression i n the associated evaporite assemblages. Certain anhydrous evaporites, including anhydrite, glauberite, and thenardite, lack absorption bands in the visible and near-infrared wavelength range, and crusts compose d of these minerals could not be characterized by using AVIRIS. In the se situations, thermal-infrared remote sensing data may complement vis ible and near-infrared data for mapping evaporites. Another problem oc curred in wet areas of Death Valley, where water absorption caused low signal levels in the 2.0-2.5 mum wavelength region that obscured any spectral features of evaporite minerals. Despite these difficulties, t he results of this study demonstrate the potential for using AVIRIS an d other imaging spectrometer data to study playa chemistry. Such data can be useful for understanding chemical linkages between evaporites a nd ground waters, and will facilitate studies of how desert ground-wat er regimes change through time in response to climatic and other varia bles.