Journal
EARTH SURFACE PROCESSES AND LANDFORMS
Volume 40, Issue 9, Pages 1202-1215Publisher
WILEY
DOI: 10.1002/esp.3713
Keywords
cosmogenic nuclides; erosion rate; glacial erosion
Funding
- Agence Nationale de la Recherche [ANR-08-BLAN-0303-01]
- Institut National des Sciences de l'Univers SYSTER program
- Agence Nationale de la Recherche (ANR) [ANR-08-BLAN-0303] Funding Source: Agence Nationale de la Recherche (ANR)
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Deciphering the complex interplays between climate, uplift and erosion is not straightforward and estimating present-day erosion rates can provide useful insights. Glaciers are thought to be powerful erosional agents, but most published glacial' erosion rates combine periglacial, subglacial and proglacial erosion processes. Within a glaciated catchment, sediments found in subglacial streams originate either from glacial erosion of substratum or from the rock walls above the glacier that contribute to the supraglacial load. Terrestrial cosmogenic nuclides (TCN) are produced by interactions between cosmic ray particles and element targets at the surface of the Earth, but their concentration becomes negligible under 15 m of ice. Measuring TCN concentrations in quartz sand sampled in subglacial streams and in supraglacial channels is statistically compliant with stochastic processes (e.g. rockfalls) and may be used to discriminate subglacial and periglacial erosion. Results for two subglacial streams of the Bossons glacier (Mont Blanc massif, France) show that the proportion of sediments originating from glacially eroded bedrock is not constant: it varies from 50% to 90% (n = 6). The difference between the two streams is probably linked to the presence or absence of supraglacial channels and sinkholes, which are common features of alpine glaciers. Therefore, most of the published mean catchment glacial erosion rates should not be directly interpreted as subglacial erosion rates. In the case of catchments with efficient periglacial erosion and particularly rockfalls, the proportion of sediments in the subglacial stream originating from the supraglacial load could be considerable and the subglacial erosion rate overestimated. Here, we estimate warm-based subglacial and periglacial erosion rates to be of the same order of magnitude: 0.39 +/- 0.33 and 0.29 +/- 0.17 mm a(-1), respectively. Copyright (c) 2015John Wiley & Sons, Ltd.
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