1 Introduction

Cycles of glaciation drive in-situ stress changes in underlying bedrock as glaciers advance, erode, and retreat, generating damage in adjacent rock slopes and influencing paraglacial slope stability. Glacial debuttressing is frequently implicated as a trigger for paraglacial rock slope failures, despite commonly observed large lag-times between deglaciation and the timing of failure and often without clear mechanical reasoning. Rock slope damage generated during glacial cycles is hypothesized to have a strong role in preparing rock slope failures, however, the mechanics of paraglacial rock slope damage remain poorly characterized.

Glacial cycles mechanically load and unload proximal rock slopes by the changing weight of ice, and in addition produce strongly varying thermal and hydraulic rock-surface boundary conditions tied to the fluctuating glacier (Fig. 1). Bedrock beneath temperate glacier ice maintains near isothermal surface temperatures at ~0 °C. Glacier retreat exposes rock walls to new thermal boundary conditions with strongly varying daily and seasonal cycles, a transition we term paraglacial thermal shock. Temperature changes generate thermal strain, inducing thermo-mechanical stresses capable of generating rock mass damage. In addition, high subglacial water pressures near the ice overburden level prevail at the base of temperate glaciers, and affect groundwater conditions in proximal valley flanks. Groundwater recharge by precipitation and snowmelt raises the water table seasonally, which is superposed on changes in hillslope groundwater tied to varying glacial ice elevations. Changing cleft water pressures control effective stresses and the strength of rock mass discontinuities. Together, these thermo-hydro-mechanical stresses act in concert with glacial loading cycles to generate rock slope damage, preparing slopes for future failure.

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