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Sidewall erosion: Insights from in situ ‐produced 10 Be concentrations measured on supraglacial clasts (Mont Blanc massif, France)
Author(s) -
Sarr A.C.,
Mugnier J.L.,
Abrahami R.,
Carcaillet J.,
Ravanel L.
Publication year - 2019
Publication title -
earth surface processes and landforms
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.294
H-Index - 127
eISSN - 1096-9837
pISSN - 0197-9337
DOI - 10.1002/esp.4620
Subject(s) - rockfall , erosion , geology , massif , geomorphology , drainage basin , clastic rock , debris , hydrology (agriculture) , physical geography , structural basin , geochemistry , landslide , geotechnical engineering , geography , oceanography , cartography
Sidewall erosion because of rockfalls is one of the most efficient erosional processes in the highest parts of mountain ranges; it is therefore important to quantify sidewall erosion to understand the long‐term evolution of mountainous topography. In this study, we analyse how the 10 Be concentration of supraglacial debris can be used to quantify sidewall erosion in a glaciated catchment. We first analyse, in a glaciated catchment, the cascade of processes that move a rock from a rockwall to a supraglacial location and propose a quantitative estimate of the number of rockfalls statistically mixed in a supraglacial sand sample. This model incorporates the size of the rockwall, a power law distribution of the size of the rockfalls and the mean glacial transport velocity. In the case of the Bossons glacier catchment (Mont Blanc massif), the 10 Be concentrations obtained for supraglacial samples vary from 1.97 ± 0.24 to 23.82 ± 1.68 × 10 4 atoms g −1 . Our analysis suggests that part of the 10 Be concentration dispersion is related to an insufficient number of amalgamated rockfalls that does not erase the stochastic nature of the sidewall erosion. In the latter case, the concentration of several collected samples is averaged to increase the number of statistically amalgamated rockfalls. Variable and robust 10 Be‐derived rockwall retreat rates are obtained for three distinct rockfall zones in the Bossons catchment and are 0.19 ± 0.08 mm year −1 , 0.54 ± 0.1 mm year −1 and 1.08 ± 0.17 mm year −1 . The mean 10 Be retreat rate for the whole catchment (ca. 0.65 mm year −1 ) is close to the present‐day erosion rate derived from other methods. © 2019 John Wiley & Sons, Ltd.