Glacier retreat and fluvial landscape response

Abstract

This thesis investigates the planform response of proglacial fluvial systems to deglaciation, specifically in northwest North America. Increase glacier retreat is extremely widespread today, drawing our attention to proglacial environments. Fluvial systems are being directly impacted by increasing rates of glacier retreat, resulting in changes to discharge, erosion and deposition, and sediment supply. It is important to understand how fluvial systems are going to reconfigure their geometries in response to these changing parameters and to help identify and assess future behaviour. Fluvial response to deglaciation was studied by two experiments, first focusing on the response to an instantaneous and dramatic change in discharge without a concomitant change in sediment supply, and second, focusing on slower changes, where sediment supply may have altered. In the first experiment, a rapid drop in discharge in Ä'ay Chu ("ay-CHEW", formerly known as Slims River) decreased the overall braiding complexity, while a rapid increase in discharge to Kaskawulsh River increased the braiding complexity. Further, alluvial fans in the Kaskawulsh River valley were eroded due to the wider active braid plain, while fans within Ä'ay Chu underwent minimal changes. In the second experiment, at 9 of 11 locations, where changes over multiple decades occurred, braiding intensity markedly decreased as proglacial lake area increased, also increasing the number of wide channels at the expense of narrower ones. The remaining two locations slightly increased in braiding intensity without ever forming a proglacial lake (control sites). This appears to be a ubiquitous trend in glaciated regions, as retreat affects sensitive proglacial rivers by disrupting the flow of discharge and sediment supply. Glacier retreat has resulted in drainage reorganization, directly altering levels of flow, and caused the formation of proglacial lakes, altering discharge and sediment supply to the rivers inducing geomorphic changes. These alluvial river systems have reconfigured their geometry in response to changing discharge and sediment supply.