Sedimentology and Stratigraphy of Glacial Lake Souris, North Dakota: effects of a glacial-lake outburst
Date of Award
Doctor of Philosophy (PhD)
Glacial-lake outbursts commonly occurred along the southern margin of the Laurentide Ice Sheet as ice-marginal lakes suddenly drained. These outbursts released huge volumes of water with tremendous erosive potential, forming large trench-shape channels. Although glacial-lake spillways have been studied in detail, the effects of outbursts on downstream lakes have not. The purpose of this study was to demonstrate the effects of the Glacial Lake Regina outburst on the lake that received the flows, Glacial Lake Souris.
Glacial Lake Souris, located in what is now North Dakota, was inundated by about 74 km3 of water carrying 25 km3 of sediment from the outburst of Lake Regina (Saskatchewan). Prior to the outburst, the bottom of Lake Souris was irregular with two shallow depressions and comprised of diamicton overlain by silt and clay rhythmites. Quiet-water lake sedimentation was abruptly halted by coarse-grained outburst sedimentation.
Based on surficial mapping, subsurface sample collection, and textural analyses, the outburst sediments have been grouped into three lithofacies: 1) matrix-rich gravel, commonly with lignite, that generally occurs at the base of the outburst sediments; 2) matrix deficient gravel, generally without lignite, that occurs near the ground surface adjacent to the Souris spillway; and 3) sand, the most widespread lithofacies, that tends to overlie other lithofacies. Lignite particles are abundant in much of the sand; at depth, outsize lignite clasts are common.
Three major depositional processes probably are responsible for deposition of the outburst sediments: braided rivers, low-density turbidity currents (the dominant process), and high-density turbidity currents or modified grain flows. Most high-density flows resulted directly from the influx of the outburst or from continuous avalanching due to rapid sedimentation. Low-density turbidity currents occurred for the entire duration of the outburst and were caused by the continuous influx of sediment-laden flows and by residual currents from high-density flows.
The emptying of Lake Souris was triggered by inundation of the lake by outburst waters before silt- and clay-size sediment had time to settle out. Incision of the lake bottom by outburst flows occurred concurrently with falling lake level.
Lord, Mark L., "Sedimentology and Stratigraphy of Glacial Lake Souris, North Dakota: effects of a glacial-lake outburst" (1988). Theses and Dissertations. 183.