Drumlins and Large-Scale Flutings Related to Glacier Folds

Abstract

A brief review of the possible mechanisms of drumlin formation leads to the conclusion that several are plausible. The universality of the generally accepted assumptions that drumlins are formed by lodgment under wet-based glaciers is questioned, and the alternatives that, in some cases, formation may be under cold-based conditions with final deposition by melt-out should be considered. This has bearing on the preservation of the landform beneath active ice. With respect to drumlins and flutings composed of materials transported by ice, the fundamental issue is to explain how these materials are agglomerated. Folding with fold axes parallel to the downglacier flow direction in zones of constricted flow is proposed as one mechanism of agglomeration. This mechanism is shown to produce the type of secondary flows that have been deduced from the internal structure of drumlins and flutings. The hypothesis is supported by observations on surface morphology, debris distribution, foliation patterns, and moraine characteristics of some glaciers in Switzerland. Drumlins are interpreted to result from three-dimensional flows and flutings from two-dimensional flows. Lateral moraines termed Röthlisberger-Schneebeli moraines, are formed partly by transverse flows and are essentially half drumlins or flutings. Some fields of drumlins and flutings are shown to occur in constricted areas of former ice flows. Details of the cross-profiles of some ice-molded landforms are explained in terms of secondary flows.