CHARACTERIZATION OF PROGLACIAL SEDIMENTS IN MOUNT RAINIER NATIONAL PARK, WASHINGTON

Mount Rainier is the most glaciated mountain in the continental United States. This study examines the impact of glacier geometry on sediment production and transport. We divide glacial geometries into two categories: valley and ridge glaciers. Sediment distribution was mapped and described in the proglacial areas of one ridge glacier and three valley glaciers; ongoing work will incorporate additional glaciers into our study. At each glacier, samples were collected at 10-m intervals along a cross-valley transect perpendicular to glacial flow. At each site, we measured the diameter of the ten largest clasts, and ten randomly-selected clasts. We measured the length of the a, b, and c axes of ten more randomly-selected clasts, where the a and b axes are defined as the longest and second longest axes, respectively. Based on published methodologies, we interpreted an a-b ratio greater than or equal to 1.4 as indicative of subglacial transport. Our preliminary results show the ridge glacier has a higher percentage of sites that averaged 1.4 or greater, and a higher transect-averaged a-b ratio overall. Using the techniques described above, the average clast size for ridge glaciers is smaller, averaging 270 mm compared to 350 mm for valley glaciers; additional grain-size analyses will confirm these results. Lower a-b ratios of valley-glacier sediment may reflect the influence of subglacial fluvial processes or the contribution of rockfall and supraglacial debris to the proglacial area. Future work will include sedimentary characterization of additional proglacial areas. Results from this work will clarify the relative importance of supraglacial and subglacial processes in sediment transport in Mount Rainier National Park.