CGRG Bibliography of Canadian Geomorphology
Search Results
Author : Bik, M.J.J.
Date : 1969
Title : The origin and age of the prairie mounds of southern Alberta
Publication : Biuletyn Peryglacjalny
Issue : 19:
Page(s) : 85-130
Abstract
The distribution of prairie mounds in the Foremost-Cypress Hills area in particular and in the area between the Cypress Hills and Edmonton in general, is described and analyzed. Earlier hypotheses of super- or subglacial origin of the prairie mounds do not account for the breaches of the mound rim and cannot explain their occurrence on both glacial and proglacial deposits. A periglacial mechanism of formation is more likely. In aspect of form the prairie mounds are similar to, but not identical with the collapsed pingos of western Europe. However, there is an excess of material in the former. The low Atterberg limits of the till of the mounds of the Foremost-Cypress Hills area, and the high content in montmorillonite of tbe clay fraction suggest that subsurface displacement of this material under supersaturated conditions is probable. The frost-heave potential of the till of the mounds is substantial and ice-lenses of considerable thickness could have formed in it. The parent relief of the mound fields was probably a rolling till plain or lacustrine plain with low internal relief. Under periglacial climatic conditions, ice segregation would start earlier and continue longer below the depressions than beneath the convexities of such a relief, if the till is saturated with water. Below the downwards advancing freezing front supersaturation occurs only when ice segregation has ceased; it ensues earlier under the convexities than beneath the depressions of the parent relief. The "eruption" and subsurface movement of deposits towards the mound sites is explained from the formation of "closed systems" of supersaturated till between an arched permafrost front above and a remnant permafrost layer or a hardrock surface below. The majority of prairie mounds occurs in belts that regionally run parallel to proglacial lacustrine deposits; these belts appear to be located in the shore-zones of former proglacial lakes. In the Foremost-Cypress Hills area the deposits of a proglacial lake along the margin of which mound fields formed, are less than 20,600 years old. The minimal age of the prairie mounds was determined to be 12,500 years.
Bibliography of Canadian Geomorphology