PRELIMINARY LIMNOGEOLOGICAL CHARACTERIZATION OF GLACIAL EROSION AND ENVIRONMENTAL CHANGE FROM SEDIMENT CORES, SWIFTCURRENT LAKE, GLACIER NATIONAL PARK, MONTANA

Glaciers are important geomorphic agents in alpine landscapes, carving U-shaped valleys and creating bedrock overdeepenings that are signatures of glacial erosion. In addition to subglacial processes such as abrasion and quarrying, supraglacial erosion of steep valley headwalls results from avalanching ice and rock. Quantifying rates of glacial erosion is difficult, but sediment cores collected from lakes downstream may yield important information on changing rates of erosion in catchments. In addition, lake cores can yield information about local climate, forest fire history, and ecosystem change over time. In summer 2005 we collected sediment cores from Swiftcurrent Lake and Lake Josephine, located near Many Glacier on the eastern side of Glacier National Park, Montana. A total of ~20 meters of sediment was retrieved. Swiftcurrent Lake is the most distal of four lakes currently receiving sediment influx due to erosion of Proterozic Belt Supergroup bedrock by Grinnell Glacier.

Here we characterize the erosive history of Grinnell Glacier during recent glacial retreat through sedimentological and mineralogical analyses of lake sediments. Age models based on radiocarbon dating and tephrachronological fingerprinting of a thick Mazama Ash layer (~7500 ybp) suggest the longest Swiftcurrent Lake core spans ~10,000 years. Changes in mineralogical composition of sediments sequences may be used to track glacial retreat through the varying lithologies of the Grinnell Glacier valley. Environmental change, well-documented in the Park over the past century, is compared to charcoal layers, grain size changes, and sedimentation pulses documented in the cores.