MAPPING PLAYA EVAPORITE MINERALS AND ASSOCIATED SEDIMENTS IN DEATH-VALLEY, CALIFORNIA, WITH MULTISPECTRAL THERMAL INFRARED IMAGES

Efflorescent salt crusts and associated sediments in Death Valley, Cal ifornia, were studied with remote-sensing data acquired by the NASA th ermal infrared multispectral scanner (TIMS). Nine spectral classes tha t represent a variety of surface materials were distinguished, includi ng several classes that reflect important aspects of the playa groundw ater chemistry and hydrology. Evaporite crusts containing abundant the nardite (sodium sulfate) were mapped along the northern and eastern ma rgins of the Cottonball Basin, areas where the inflow waters are rich in sodium. Gypsum (calcium sulfate) crusts were more common in the Bad water Basin, particularly near springs associated with calcic groundwa ters along the western basin margin. Evaporite-rich crusts generally m arked areas where groundwater is periodically near the surface and thu s able to replenish the crusts though capillary evaporation. Detrital silicate minerals were prevalent in other parts of the salt pan where shallow groundwater does not affect the surface composition. The surfa ce features in Death Valley change in response to climatic variations on several different timescales. For example, salt crusts on low-lying mudflats form and redissolve during seasonal-to-interannual cycles of wetting and desiccation. In contrast, recent flooding and erosion of rough-salt surfaces in Death Valley probably reflect increased regiona l precipitation spanning several decades. Remote-sensing observations of playas can provide a means for monitoring changes in evaporite faci es and for better understanding the associated climatic processes. At present, such studies are limited by the availability of suitable airb orne scanner data. However, with the launch of the Earth Observing Sys tem (EOS) AM-1 Platform in 1998, multispectral visible/near-infrared a nd thermal infrared remote-sensing data will become globally available .