GEOCHEMICAL AND FIELD IDENTIFICATION OF A LANDSLIDE AT STEAMBOAT ROCK, WASHINGTON USING PORTABLE X-RAY FLUORESCE

An approximately 24,000 square meters section at the north tip of Steamboat Rock slid about 130 meters downslope. This large landslide likely occurred sometime during, or following the catastrophic draining of glacial Lake Columbia/ Missoula floods. Samples taken from the slump block were analyzed using portable x-ray fluoresce. Geochemical results were correlated to the stratigraphy along the basaltic cliff to help estimate the offset and to confirm that the block is a landslide deposit. Geochemical composition of the basalt was estimated using a new calibration developed between Bruker and Eastern Washington University, based on samples from eastern Washington that had previously been measured at the Peter Hooper GeoAnalytical Laboratory at WSU. The mass wasting event may have been due to preferential erosion of interbeds and/or possibly weathered granitic bedrock at the headward side of the Steamboat Rock during the Missoula Floods.