Comparison of moraines formed by surging and normal glaciers

Abstract

A Neoglacial moraine of Bighorn Glacier, St. Elias Mountains, Yukon, probably formed by a surging glacier, and a Neoglacial normal moraine of nearby Grizzly Glacier were studied. Surficial deposits and erosional features were mapped, Fabric analyses were done in till at five sites in each moraine. Samples were subjected to laboratory lithologic and texture analyses.The Bighorn (surge) moraine is a thin, discontinuous, irregular mantle, mostly till, but including ice-contact stratified material. Lateral moraines show subdued ridges marking the upper limit of glaciation. Ground moraine of the Grizzly (normal) glacier is an irregular, continuous, thick mantle, mostly till and. ice-contact stratified material. Upper ice limits are marked by prominent ridges. Rocks of similar lithologies within the till are concentrated in bands parallel to glacier flow.Stones in till of the Grizzly moraine have strong preferred orientation roughly in the direction of glacier flow. In the Bighorn moraine, rocks in till are weakly oriented. Where orientation is apparent, it is not necessarily in the flow direction. For the size fraction finer than 2 mm, Bighorn till is coarser than Grizzly till although the bedrock terrain is similar.These differences are useful in distinguishing moraines of normal and surging glaciers.