GEOMORPHIC CONTROLS ON THE SPATIAL DISTRIBUTION OF DEBRIS FLOWS IN PROGLACIAL DRAINAGES AT MOUNT RAINIER, WA

Although all proglacial drainages within Mount Rainier National Park are considered at risk for debris flow initiation, only certain drainages have apparent evidence of debris flow activity. This research uses field work and remote sensing techniques to explain the spatial distribution of debris flows in the West Fork White River, Winthrop Creek, South Puyallup River, and Tahoma Creek drainages. Field work includes the documentation of clast size, angularity, and composition in transects across proglacial river valleys. Clast size distribution in select transects suggest some geomorphic processes are dominant over others, but additional data are needed to confirm these results. Remote sensing work includes using Google Earth Pro to measure channel width, valley area, and available sediment area in each proglacial drainage. Our results suggest that the ratio of available sediment area to valley area can be used to highlight debris flow risk; measurements of the South Puyallup River drainage yielded a ratio of 2:1, while the same analysis produced a ratio of 4:1 for Tahoma Creek - a drainage with a well-documented debris flow history. A relationship may exist between terminus retreat distance and debris flow initiation, as glacial retreat increases the amount of readily-mobilized sediment. Remote sensing methodologies show promise in identifying locations with a higher risk of debris flow activity.