Report

Erosion by an Alpine glacier

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Science  09 Oct 2015:
Vol. 350, Issue 6257, pp. 193-195
DOI: 10.1126/science.aab2386

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  • Glacial erosion report overlooks the role of quarrying in shaping mountain landscape

    Herman et al. (Report, 9 October, 2015, p.193) use continuously measured suspended load in glacial meltwater with ice velocity measurements to determine that glacial erosion is a function of the square of the sliding velocity for the Franz Josef Glacier, a fast flowing glacier in New Zealand. This is a significant step forward in work to constrain the constants and parameters of a glacial erosion law. Based on a comparison between this non-linear erosion law and a pseudo-linear quarrying model proposed by Iverson (1), the authors argue that abrasion must dominate over other processes in fast-flowing glaciers. However, the glacial erosion rate they derive is based on suspended sediment load, which samples fine sediment produced mainly by abrasion, and does not capture bed load produced by quarrying. In addition, a significant portion of the fine sediment may come from quarried clasts as they are worn down when acting as tools in the abrasion process. We suggest that their derived erosion rates are minimum estimates of the total glacial erosion and that their data can be interpreted as indicating that quarrying is at least as important as abrasion in removing rock from a glacier bed.
    In a glacial environment, suspended sediment measurements focus on fine-grained material produced mainly by abrasion, and do not capture bed load (large clasts) that are produced mainly by quarrying. Sub-rounded large clasts and boulders are commonly observed both in glacial meltwater...

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    Competing Interests: None declared.

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