GEOMORPHOLOGIC AND PALEOENVIRONMENTAL CHANGE IN THE MANY GLACIER REGION, GLACIER NATIONAL PARK, MT

Understanding controls on past climate variability is key to assessing potential future environmental change. Results from a ~12,900 year long core collected in 2005 from Swiftcurrent Lake (located downstream of Grinnell Glacier in the Many Glacier region of Glacier National Park, Montana) show evidence of prominent climate swings reflected in the total organic carbon content (MacGregor et al., in press). Dolomite presence in the Swiftcurrent core may reflect the position of Grinnell Glacier over time. However, the presence of three proglacial lakes between the glacier and Swiftcurrent Lake, and the likelihood of hillslope contributions to the hydrologic system, make the correlation problematic.

In July 2010, we brought seven undergraduates to the Park to collect additional cores from Swiftcurrent Lake, as well as from the upstream Lake Josephine and lower Grinnell Lake. The goal of this research was to test the relationship between climate fluctuations and lake sediment variables, such as organic carbon content and wildfire-related charcoal flux; enhance our understanding of the connections between lakes within the Grinnell Glacier watershed, and between glacial erosion and downstream lake sedimentation; and assess the human impacts on the watershed through collection and dating of near-surface sediments.

A ~8-m long core from Swiftcurrent Lake was several meters longer than previously collected, and contained three volcanic ash layers. Surface cores from Swiftcurrent, Josephine, and lower Grinnell lakes will be dated using lead-210, providing controls on modern sedimentation rates and helping constrain human impacts near the Many Glacier Hotel, longstanding car camping and other tourism facilities, and Park roads. A ~4-m long core from steep-sided lower Grinnell Lake shows periods of quiescent fine-grained sedimentation as well as sandy and woody debris flow units. Gravel clasts found in the absence of other coarse material suggest ice-rafted debris from valley wall rockfalls may be important in the geomorphic history of the basin. Alternating pink and dark gray layering in the Lake Josephine core likely reflects variability in the source rock feeding the lake, and may show changing geomorphic forcing to the valley hydrologic system.