GLACIAL DISPERSAL PATTERNS AND NUMERIC MODELING; A COMBINED APPROACH TO INTERPRETING LARGE-SCALE PATTERNS OF SUBGLACIAL EROSION AND DEPOSITION

Qualifying and quantifying the large-scale spatial distribution of subglacial erosion and deposition is a vital step in understanding the relationship between ice dynamics, process mechanics, and the landforms and sediments preserved in the geologic record. Due to the inaccessibility of the subglacial transport zone in modern glaciers, this study uses a combination of numeric modeling and field studies in glaciated basins to interpret the spatial distribution of subglacial processes.

A simple one-dimensional numeric model of the subglacial transport system was designed to simulate glacial dispersion patterns for given bedrock sources along a flowline of an alpine paleo-glacier and to test models for the spatial distribution of erosion and deposition processes. The model assumes that the only input of material to the subglacial sediment stream is the bedrock at the glacier bed and that sediment is passively transported to the glacier margin for deposition. The model algorithm assumes that the amount of material added to the sediment stream increases in a linear fashion downglacier.

Modeled dispersal curves were compared to dispersion patterns preserved in the Middle Quartz Creek Valley of the Sawatch Range, Colorado. This valley was chosen because: the glaciated basin is small enough so that the entire glacial system could be studied; a glacier is no longer present in the modern system; and the bedrock geology is diverse with a complex structure. Samples were taken at 200-meter intervals along a glacial flowline and rock fragments from subglacial till were used to create dispersal curves. The standard deviation of differences between paired-observations was less than 6% between the modeled and observed glacial dispersal patterns. This close correlation suggests that a model based only on the simple addition of material can accurately simulate complex glacial dispersal patterns.