REMOTE SENSING AS A TOOL FOR GEOLOGIC MAPPING AT MOUNT ST. HELENS, WASHINGTON

Remotely sensed data have been successfully employed in geologic mapping, ranging from mapping rock types on a broad regional scale (e.g. Abrams et. al., 1977; Savage and Fischer, 1998), to mapping smaller local features such as delineating flow boundaries in historic basaltic lava flows, determining mineral abundances, and classifying felsic plutons (e.g. Realmuto et. al., 1992; Hamilton and Christensen, 2000; Hook et. al., 2001; Michalski et. al., 2001). Remotely sensed data can significantly aid the on-going geologic mapping effort at Mount St. Helens by providing a high-resolution textural and compositional view of the volcano's proximal pumice plain and amphitheater crater. Mount St. Helens has been the most active volcano in the Cascade Range in the past 4,000 years, but despite the attention that has been focused on it because of its eruption in 1980, a modern detailed geologic map of the volcano is not yet available. Understanding the past eruptive behavior of the volcano is the key component for assessing the impacts of future events, thus an accurate and detailed geologic map is critical to a thorough volcano hazards assessment. Spectroscopic data can help to delineate the boundaries of the northward-directed lateral blast deposits and pyroclastic flows associated with the 1980 eruptions and subsequent lahars on the pumice plain and to help map the core of the volcanic edifice as it outcrops in the amphitheater crater. We are employing remotely sensed data from a combination of instruments, including orthorectified aerial photographs, Landsat 7 Thematic Mapper, AVIRIS, TIMS, and MASTER. Geologic mapping of the pumice plain and crater is being compiled in a GIS as a digital database so it can easily be compared to and combined with other geospatial data to visualize the geology and assess volcano hazards and their potential effects at Mount St. Helens. If these methods prove successful, they can be applied to other Cascade volcanoes.