Paraglacial reworking of lateral moraine slopes, sharp-crested lateral moraines and alluvial fans buttressed by lateral moraines

Abstract

The ongoing retreat of alpine glaciers has exposed large quantities of glacial sediments prone to paraglacial geomorphic processes. Lateral moraines are key features of these glacial landscapes. Studies on the paraglacial reworking of lateral moraines are rare; consequently, their transformation is relatively undocumented. However, as deglaciation in alpine regions increases the requirement for a fuller understanding of paraglacial response increases as well. This is due to a need to understand the complex geomorphological responses to deglaciation. To document typical examples, analyze the morphological setting and provide an analysis of lateral moraine paraglacial reworking in deglaciating regions of the United States, Canada, Asia, Afghanistan, Argentina and Switzerland, analysis ready data from GIS software packages was utilized. Paraglacial adjustment is evident through the development of gullying, primarily on the proximal moraine slope. Gully slope and length increase with moraine height. The proximal slope had a steeper angle of repose compared to the distal slope. The erosional activity as well as the more or less in activity is a reflection of slope stability. Sharp-crested lateral moraines were defined within the context of slope profile and captured within selected regions. Extensive paraglacial modification by debris flows was limited to sections of the glacial valley where valley wall slopes gradients are steep. The slope profile of moraines, with a gentler lower slope, an intense gullied upper section and a sediment deposit at the bottom of the proximal slope was more prevalent towards the glacier terminus. There, moraines are either devoid of vegetation colonization or vegetation colonies are well established. Up-glacier moraines have little or no distal slope and are devoid of vegetation on both slopes. The general form of the moraines establishes that there are many feedbacks, between position and geomorphic activity on a moraine, that influence the paraglacial process.