High-Resolution Seismic Stratigraphy of Lake Mcdonald, Glacier National Park, Montana, U.S.A.
Mullins HT, Hinchey EJ, Eyles N. 1991. High-Resolution Seismic Stratigraphy of Lake Mcdonald, Glacier National Park, Montana, U.S.A.. Arctic and Alpine Research. 23(3):311-319
A high-resolution, "uniboom" seismic reflection survey of the largest lake (Lake McDonald) in Glacier National Park, Montana, has determined the thickness and nature of the sediment fill beneath the lake as well as the form of the underlying bedrock surface. The bedrock surface below the lake is distinctly V-shaped and contains a narrow, axial thalweg eroded as much as 279 m below lake level. Although a significant portion of the sediment fill is acoustically impenetrable (possibly due to gas-saturated sediment), four seismic stratigraphic sequences have been identified. The oldest (I) is restricted to the steeply sloping bedrock walls of the basin and correlates with lateral moraine ridges on the margins of the lake that record retreat of the late Wisconsin valley glacier. Younger sequences (collectively up to 150 m thick) occur along the axial portion of the basin and distinctly onlap sequence I and/or bedrock. Sequences II and III are characterized by alternations of highly reflective and reflection-free seismic facies whereas sequence IV consists exclusively of high-frequency parallel reflections. Sequences II and III are interpreted as fine-grained, proglacial lake sediments deposited from a glacier-fed river during final ice retreat from the basin. Sequence IV likely records a strongly seasonal postglacial sedimentation regime. Lake McDonald differs from other seismically investigated glaciated lake basins by its paucity of chaotic debris and a relatively simple infill stratigraphy. The nature of the bedrock surface and proglacial sediment fill may record the erosional and depositional significance of subglacial and proglacial meltwater activity. The thick stratigraphy beneath Lake McDonald likely contains a detailed record of glacial and environmental change for this portion of the Rocky Mountains.
- Type
- Journal Article
- Authors
- Mullins, Henry; Hinchey, Edward; Eyles, Nicholas
- Units
- GLAC
- Keywords
- Geophysical Surveys, Lake McDonald Glacier National Park MT, Lakes & Ponds, Physical Sciences, Stratigraphy