Hydromechanical Rock Slope Damage During Late Pleistocene and Holocene Glacial Cycles in an Alpine Valley

Abstract

Subglacial water pressures influence groundwater conditions in proximal alpine valley rock slopes, varying with glacier advance and retreat in parallel with changing ice thickness. Fluctuating groundwater pressures in turn increase or reduce effective joint normal stresses, affecting the yield strength of discontinuities. Here we extend simplified assumptions of glacial debuttressing to investigate how glacier loading cycles together with changing groundwater pressures generate rock slope damage and prepare future slope instabilities. Using hydromechanical coupled numerical models closely based on the Aletsch Glacier valley in Switzerland, we simulate Late Pleistocene and Holocene glacier loading cycles including long‐term and annual groundwater fluctuations. Measurements of transient subglacial water pressures from ice boreholes in the Aletsch Glacier ablation area, as well as continuous monitoring of bedrock deformation from permanent Global Navigation Satellite Systems stations, help verify our model assumptions. While purely mechanical glacier loading cycles create only limited rock slope damage in our models, introducing a fluctuating groundwater table generates substantial new fracturing. Superposed annual groundwater cycles increase predicted damage. The cumulative effects are capable of destabilizing the eastern valley flank of our model in toppling‐mode failure, similar to field observations of active landslide geometry and kinematics. We find that hydromechanical fatigue is most effective acting in combination with long‐term loading and unloading of the slope during glacial cycles. Our results demonstrate that hydromechanical stresses associated with glacial cycles are capable of generating substantial rock slope damage and represent a key preparatory factor for paraglacial slope instabilities.

Topographic and Geologic Controls on Frost Cracking in Alpine Rockwalls

“…The problem of cracking is associated with initial conditions associated with rock structure (Anderson et al., 2013). Cracks can be generated by tectonic stress (Molnar et al., 2007), paraglacial stress release (Grämiger et al., 2017; Grämiger et al., 2020), and internal stress distribution (Leith et al., 2014a, 2014b) following glacier retreat or surface processes (Clarke & Burbank, 2010, 2011). Cracks also develop progressively (Walder & Hallet, 1985) and therefore initial conditions will be far away from assumed constant cracks.…”

The Landslide Hazard Chain in the Tapovan of the Himalayas on 7 February 2021

“…Widespread recession of glaciers is occurring on the plateau as a result of climate change and anthropogenic forcing (IPCC, 2013(IPCC, , 2019Marzeion et al, 2014;Wang et al, 2021;Zemp et al, 2019). As glaciers melt, accelerated water infiltration into the superficial geomaterials (Grämiger et al, 2020) and permafrost thaw (Gruber et al, 2004) take place, resulting in reduced strengths of the geo-materials and hence landslides at high altitudes. At about 10:00 a.m. local time (04:30 GMT) on February 7, 2021 (Martha et al, 2021), an enormous landslide occurred near Nanda Ghunti (  30.37 N,  79.73 E) in India's Chamoli District (Figure 1a).…”

Topographic and geologic controls of frost cracking in Alpine rockwalls

“…The problem of cracking is associated with initial conditions associated with rock structure (Anderson et al, 2013). Cracks can be generated by tectonic stress (Molnar et al, 2007), paraglacial stress release (Grämiger et al, 2017;Grämiger et al, 2020), and internal stress distribution (Leith et al, 2014a(Leith et al, , 2014b following glacier retreat or surface processes (Clarke & Burbank, 2010. Cracks also develop progressively (Walder & Hallet, 1985) and therefore initial conditions will be far away from assumed constant cracks.…”