MEDIAL MORAINE CONTRIBUTIONS TO THE CONSTRUCTION OF END MORAINES, MATANUSKA GLACIER, ALASKA

This study seeks to understand the role of supraglacial contribution on moraine construction and resedimentation processes. Lawson’s (1979 and 1982) studies on resedimentation at the Matanuska Glacier focused mostly on moraines proximal to the clean ice margin (almost no supraglacial debris cover) where sediment contributions to the moraines are primarily from the subglacial and basal ice systems. His research culminated in a classification scheme for four distinct types of sediment flows. However, a supraglacial contribution to moraines may result in significantly different resedimentation processes from those Lawson reported, resulting in different characteristics of the end moraines. For instance, sediment containing an increased amount of larger, angular clasts (supraglacial in origin) may be likely to have a lower water content than subglacial silts, and may result in more spallation, ice slope colluvium, and type I sediment flows. Measurements and samples were obtained at six moraine exposures on a transect oriented roughly perpendicular to ice flow. Some of these sites lie directly downglacier from a medial moraine, which contributes significant amounts of supraglacial sediment to the moraine systems. Fabric analyses, pebble roundness counts, and grain size analyses have all been performed in order to constrain sediment characteristics. Initial results indicate that supraglacially derived sediment has a larger presence in the moraines proximal to the medial moraineand that this results in specific resedimentation processes.