MELTING MOUNTAINS: LIDAR MAPPING AND CHARACTERIZATION OF THE PERIGLACIAL DEBRIS FLOWS on MT. RAINIER, WASHINGTON AND MT. HOOD, OREGON

In November of 2006 an intense tropical rainstorm inundated the Pacific Northwest triggering numerous debris flows on the flanks of several of the Pacific Northwest volcanoes, including Mt. Rainier and Mt. Hood. The debris flows initiated in areas that had been recently exposed by glacier recession and hence are referred to as “periglacial” debris flows. Airborne LiDAR data were acquired over the region in fall 2007 and 2008. The LiDAR elevation data provide key information for characterizing the geomorphology of the initiation sites, and have allowed us to quantify upslope-contributing area, channel and side slope gradients, and to simulate downstream flow patterns. When compared with traditional USGS digital elevation model (DEM) data, the LiDAR DEM shows a clear relationship between upslope contributing area and debris flow initiation, whereas the USGS DEM analyses do not. The elevation data have also been merged with multi-year satellite-derived maps of glacier extent for improved geo-visualization and to identify areas of potential future debris flow initiation. Qualitative analysis of the LiDAR intensity images appear to indicate that intensity can also be used to map the transition from erosion to deposition in channels where debris flows have recently occurred.