Subglacial Quarrying Erosion: Flawed Ideas Fixed by Intuitive Bedrock Weaknesses

The two dominant subglacial landscape-carving processes, quarrying and abrasion, are analogous to having teeth pulled vs. more slowly grinding them flat. While abrasion, like sandpapering wood, is a smoothening process and involves glaciers dragging loose rocks across subglacial bedrock, quarrying boosts landscape roughness and frictional resistance to glacial flow. It is the process by which chunks of at least somewhat intact continuous bedrock can be liberated and turned into sediments. Those sediments can then scrape along downstream, causing further erosion through abrasion. While abrasion tends to happen more extensively because it merely requires loose rocks and moving ice, quarrying tends to achieve much greater rates of mass removal, if achievable. The magnitude of these and other “what if’s” results in landscape erosion rates varying from tens of micrometers per year to centimeters per year. Where minimal quarrying is achieved, valleys can resemble their prior stream-modified V-shape, while others resemble a classic glacially-modified U-shape.

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Speaker: Roland Theiss, UC Berkeley