Date of Award
Master of Arts (MA)
The descriptive term 11washboard moraine" has been applied to small transverse till ridges occurring in glaciated regions of North America. Washboard moraines have, in the past, been confused with similar transverse features such as ribbed moraines and De Geer moraines. No previous work had been done on washboard moraines in North Dakota prior to this study. Objectives of this study were to (1) map the distribution of washboard moraines in a selected study area,(2) describe the morphology and composition of washboard moraines, (3) determine the origin !or washboard moraines, and (4) compare data obtained in North Dakota with previously published information.
Northern Nelson County, North Dakota, was chosen as the study area. Washboard moraines were mapped, sampled, measured and compared in the field. The structure of selected washboard moraines was determined by using pebble fabric analysis.
Washboard moraines in northern Nelson County are generally 4 to 15 feet high and are spaced 250 to 550 feet apart. The moraines are subdued, discontinuous, irregular ridges paralleling each other. The moraines are composed of slightly gravelly loam. The till bas unimodal, bimodal and polymodal grain-fabric distribution; preferred orientations were generally unrelated to regional ice flow direction. Some washboard moraines cross askers and drumlinoid features. Slopes ranged from 2° to 6° and showed no proximal or distal slope variation.
Based on Nelson County field observation and on studies in Greenland and Alberta, washboard moraines appear to be remnant shear moraines that were deposited from a superglacial position. Evidence of this includes (1) the crossing of some eskers and drumlinoid features by washboard moraines, (2) the discontinuous and irregular shape of washboard moraines, (3) the absence of consistent proximal and distal slope variation, and (4) the preferentially oriented till fabrics unrelated to regional ice flow. The shear moraines were formed by shearing of active ice over stagnant ice in marginal positions, forming debris-laden shear planes. Debris in the shear planes is released by ablation, forming ice-cored shear moraines.
The preservation of shear moraines during deposition is de pendent upon the plasticity of the till and the rate of ablation.
Nielsen, Dennis N., "Washboard moraines in northeastern North Dakota" (1969). Theses and Dissertations. 210.