Controls upon the location and size of glacial overdeepenings

Overdeepening is an important glaciological and geomorphological process that has the potential to influence the response of ice masses to climatic changes. We have examined several hundred glacial overdeepenings proximal to/ within Labrador, Canada, to investigate the controls upon overdeepening location and size. Our analyses show that overdeepening appears to correlate strongly with glacial confluence and, importantly, the correlation is strongest where confluence-geometry indicates the speed up of ice-flow. Further, we find that the magnitude of ice-flow speed up correlates with overdeepening depth only for confluences situated in or near major geological fault-zones. Our findings therefore support the hypothesis that overdeepening can be initiated by an increase in ice velocity. Further, we conclude that overdeepening is most efficacious where fractured bedrock enables efficient quarrying.