Beyond debuttressing: Mechanics of paraglacial rock slope damage during repeat glacial cycles

Abstract

Cycles of glaciation impose mechanical stresses on underlying bedrock as glaciers advance, erode, and retreat. Fracture initiation and propagation constitute rock mass damage and act as preparatory factors for slope failures; however, the mechanics of paraglacial rock slope damage remain poorly characterized. Using conceptual numerical models closely based on the Aletsch Glacier region of Switzerland, we explore how in situ stress changes associated with fluctuating ice thickness can drive progressive rock mass failure preparing future slope instabilities. Our simulations reveal that glacial cycles as purely mechanical loading and unloading phenomena produce relatively limited new damage. However, ice fluctuations can increase the criticality of fractures in adjacent slopes, which may in turn increase the efficacy of fatigue processes. Bedrock erosion during glaciation promotes significant new damage during first deglaciation. An already weakened rock slope is more susceptible to damage from glacier loading and unloading and may fail completely. We find that damage kinematics are controlled by discontinuity geometry and the relative position of the glacier; ice advance and retreat both generate damage. We correlate model results with mapped landslides around the Great Aletsch Glacier. Our result that most damage occurs during first deglaciation agrees with the relative age of the majority of identified landslides. The kinematics and dimensions of a slope failure produced in our models are also in good agreement with characteristics of instabilities observed in the field. Our results extend simplified assumptions of glacial debuttressing, demonstrating in detail how cycles of ice loading, erosion, and unloading drive paraglacial rock slope damage.

Post-glacial rock avalanches in the Obersee Valley, Glarner Alps, Switzerland

“…Such models allow for longer lag times, but most rely on dating to resolve the time scale of slope response rather than making predictions from rock mechanical principles (c.f. Graemiger et al, 2014).…”

Thermomechanical Stresses Drive Damage of Alpine Valley Rock Walls During Repeat Glacial Cycles

“…Synopsis of Late Glacial and Holocene glacier extents combined with spatial landslide extents mapped in the Aletsch region (modified from Grämiger et al, ): Hillshade derived from DTM (swissALTI3D by Swisstopo). Positions of rock and air temperature measurements (this study) and air temperature measurements from nearby weather stations (MeteoSchweiz) are shown.…”

“…Concept of paraglacial rock slope preparation until ultimate failure: (a) variation of driving and resisting forces in a rock slope during repeat glacial cycles. Incremental damage induced by glacier advance and retreat as purely mechanical loading and unloading (Grämiger et al, ) together with other preparatory factors during ice‐free conditions reduces slope stability until a critical state is reached. A single small disturbance may become the ultimate trigger for catastrophic failure (adapted from Gunzburger et al, and Gischig et al, ).…”

Monitoring Surface Deformation over a Failing Rock Slope with the ESA Sentinels: Insights from Moosfluh Instability, Swiss Alps

“…To evaluate the failure potential of active rock slope instabilities, a fundamental understanding of the predisposing factors and physical processes driving the slope movements and accelerations is essential [58,59]. This process understanding depends on high-resolution spatial and temporal records of slope displacements and the corresponding driving forces, such as pore pressure from rainfall and snow melt, surface temperature or glacial retreat.…”