Sidewall erosion: Insights from in situ‐produced ¹⁰Be concentrations measured on supraglacial clasts (Mont Blanc massif, France)

Abstract

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 10Be 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 10Be concentrations obtained for supraglacial samples vary from 1.97 ± 0.24 to 23.82 ± 1.68 × 104 atoms g−1. Our analysis suggests that part of the 10Be 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 10Be‐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 10Be 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.

Climatic and structural controls on Late‐glacial and Holocene rockfall occurrence in high‐elevated rock walls of the Mont Blanc massif (Western Alps)

“…inherited 10 Be concentration produced during the last glacial cycle) was an overestimation. This higher rockfall frequency is also confirmed by 10 Be measurements in supra-glacial clasts collected in Bossons and Argentière glacier areas (MBM), revealing significant rockfall erosion in glacier sidewalls (Sarr et al, 2019). We thus consider that the inherited 10 Be content in our collected samples is non-significant for exposure age computation.…”

Production and Transport of Supraglacial Debris: Insights From Cosmogenic 10Be and Numerical Modeling, Chhota Shigri Glacier, Indian Himalaya

“…The benefit of this approach is that (1) the estimated erosion rates represent values that are spatially and temporally averaged across relatively large headwall areas; (2) the source areas of the debris can be reconstructed, e.g., from remote‐sensing images; and (3) the sampling procedure is relatively straightforward. However, despite a promising initial application (Ward & Anderson, 2011), this approach has rarely been employed (e.g., Guillon et al, 2015; Sarr et al, 2019), and its applicability in different settings remains to be tested. Here we present headwall erosion rates derived from 10 Be concentrations in the ablation‐dominated medial moraine of the Chhota Shigri Glacier, Indian Himalaya.…”

Rockwall Slope Erosion in the Northwestern Himalaya

“…(2017; http://calibration.ice-d.org/) and a 10 Be half‐life of 1.387 Ma (Chmeleff 2010; Korschinek 2010). Ward and Anderson (2011) and others have demonstrated that muonic production of 10 Be within amalgamated supraglacial debris sourced from the rockwall is negligible, and for the process timescales of rockwall slope erosion can be omitted from our calculation scheme (Akçar et al., 2014; Braucher et al., 2003; Sarr et al., 2019).…”

“…This approach to quantifying rockwall slope erosion accounts only for the spallogenic component of incoming cosmic rays and assumes a negligible loss of 10 Be due to radioactive decay, and steady state erosion and 10 Be production over time (von Blanckenburg, 2005). Further details of this methodology and its assumptions are provided by Supplementary Item 1 and in Ward and Anderson (2011) and Sarr et al (2019).…”

“…Periglacial weathering processes that are driven by moisture and temperature variability, and include freeze‐thaw, frost cracking and ice wedging, are particularly critical for the detachment and disintegration of rock from rockwalls (Eppes & Keanini, 2017; Heimsath & McGlynn, 2008; McColl & Davies, 2013). This detachment is considered stochastic, and through rockfall and other mass wasting delivers debris to glacier surfaces (Gibson et al., 2017; Sanders et al., 2012; Sarr et al., 2019).…”