BASALT WEATHERING AND VEGETATION MAPPING AT CRATERS OF THE MOON NATIONAL MONUMENT: A HYPERSPECTRAL REMOTE SENSING STUDY

The Craters of the Moon (COM) volcanic field lies in south-central Idaho along the northern border of the Snake River Plain. The field consists of cinder and spatter cones and a complex central fissure system known as the Great Rift, and has multiple basaltic lava flows of Holocene to Pleistocene age (15,000 to 2,000 years). Airborne hyperspectral (224 spectral bands) AVIRIS data was collected in three parallel flight lines in July, 2004, covering most of Craters of the Moon National Monument (about 1500 square km). Approximately 40 individual, overlapping lava flows occur in the study area, the majority of which are basalts, but some compositions range up to trachytes. Each flow has distinct spectral reflectance characteristics in the AVIRIS data, and there is inter- as well as intra-flow spectral variability. These variations are largely due to variability in primary mineralogy and texture (a'a vs. pahoehoe), as well as the effects of weathering and post-emplacement mineralization (e.g. oxidation effects, conversion to clays, hydrothermal alteration zones). In addition, the lavas have variable ash, loess, and vegetation cover. In 2005, a large-scale field vegetation study was undertaken in the monument, with vegetation types and percent vegetation cover measured for over 250 individual locations in the AVIRIS study area. The goal of this study was to determine how the variations in lava flows, soils and ash, and vegetation influence the spectral properties in the imagery, and to use spectral un-mixing methods to map the proportions of each of these components.