Date of Award

1967

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Geology

First Advisor

L. Clayton

Abstract

The thesis here abstracted was written under the direction of Lee Clayton and approved by Walter L. Moore -and John R. Reid as members of the examining connnittee, of which Mr. Clayton was chairman.

In western North Dakota many drainage channels that are incised into valley fill are characterized by steep, unvegetated sides. Many such channels contain actively eroding scarps. The origin of these scarps is most frequently related to increased water velocity causing accelerated erosion on a steepened reach of the valley flat.

The principal mechanism of scarp migration is soilfall which is initiated by undercutting of the scarp face. Groundwater seepage at the base of the scarp is effective in reducing the cohesion of the sediment, thereby increasing the erodibility. In a channel with several successive scarps, the height of these scarps becomes progressively greater downstream, indicating a relationship to discharge.

Three alluvial units and two paleosols within the recent valley fill have been identified. By carbon-14 dating it was established that the upper 15 to 20 feet of chis sediment was probably deposited after A. D. 1775. An average rate of sedimentation on the order of 0.3 to 0.4 feet per year is believed to be characteristic of these units.

The modern cycle of erosion and deposit in western North Dakota probably began in the middle or late 1800's. Many of the gullies were partially or entirely filled during the deposition of the upper alluvial unit and new gullies have been trenched to their present depth since approximately 1936.

The periods of valley filling in western North Dakota were associated with periods of sub-normal precipitation. Modern precipitation records indicate that such a period occurred from 1917 to 1936 during which the upper unit was deposited.

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