Date of Award

1984

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Geology

First Advisor

A.E. Kehew

Abstract

Recent recognition of the rapid draining of numerous glacial lakes, including some in the Northern Plains, has revealed 'a need for further research concerning this process. Geomorphic interpretation of the Souris, Des Lacs, and Moose Mountain Valleys, and the gravel deposits in them, has resulted in the recognition of five phases in the development of the drainageways. Textural analyses and paleohydraulic methods were applied to the sediments associated with each phase to distinguish and characterize the discharges. Four of the five phases of development involved short-lived, high velocity (>4 m/s) discharges resulting from the rapid draining of glacial lakes; the other phase (2) involved deposition by glacial meltwater.

Phase 1 discharges (3 x 104 m3/s) initiated the development of the Des Lacs Valley; the source probably was a supraglacial lake in the vicinity of Bowbells, North Dakota. Deposits of generally unstructured sandy gravel occur relatively high on the valley walls and are confined to the lower Des Lacs and Souris spillways.

Phase 2 discharges (2.1 x 103 m3/s) deposited outwash sediment, consisting of cross-bedded gravelly sand, in the Moose Mountain and lower Souris Valley. Glacial meltwater from the Moose Mountains, which commenced when the ice sheet divided around the Moose Mountains, was the source of these flows.

Phase 3 and 4 discharges (1.9 x 104 m3/s) probably each resulted from the rapid draining of Glacial Lake Arcola. Phase 3 was an erosional stage that incised the Moose Mountain and lower Souris Valley and induced landslides along the valley walls. Deposition of unstructured pebble gravel throughout much of the lower Souris spillway occurred during phase 4. The deposits commonly are inset into the valley walls, indicating that they were later truncated by erosion.

The upper Souris Valley was developed and the lower Souris and Des Lacs spillways were enlarged during the cataclysmic discharges of phase 5 (2.0 x 105 m3 /s) from Glacial Lake Regina. Huge bars of unstructured pebbly cobble gravel were deposited during this event. Several geomorphic features associated with this phase are similar to features described in the Channeled Scabland. Phase 5 concluded the development of the spillways.

A glacial chronology proposed by Clayton and Moran (1982) indicates that the drainage described in this study occurred between 11,700 BP and 11,300 BP. Although active ice is generally assumed to have been northeast of the spillways during the time of drainage development, the presence of stagnant ice is indicated by streamlined collapse topography within a fluvially scoured zone, several inconsistencies in paleohydraulic calculations, and the abundance of landslides in the lower Souris Valley.

The information developed from this study, and the relatively recent recognition of other floods resulting from the rapid draining of glacial lakes, indicates that this form of 'instantaneous' drainage development may have been common during the Pleistocene Epoch, especially in areas of ice stagnation.

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