| Summary: | Glacier and slope instabilities pose significant hazards in mountain areas, with a high potential impact on the population. Forecasting glacier and slope instabilities remains challenging as sensing technology focusing on the surface might fail to detect damage and changes in subsurface elastic properties leading to large-scale failures. Seismic methods, such as seismic interferometry, can help address this observational gap by quantifying changes in material integrity. Here, we discuss two case studies in which seismology elucidates the development of cryospheric hazards: a hanging glacier instability and permafrost degradation on an active rockslide. We first analyze seismic data from Switzerland's Eiger hanging glacier before a 15,000 m3 break-off event. Our approach, based on an analysis of multiple icequake waveforms, allows us to measure seismic source migration. Combined with an analytical model based on damage mechanics our results quantify crevasse extension between unstable and stable ice masses. We then move to the second study site, an active rock slope near "Spitze Stei" in the Kandersteg region, Switzerland. The time series of relative seismic velocity variations (dv/v) constrain the lateral and depth-dependent extent of changes in the rock's elastic properties caused by pore pressure increase and potentially by permafrost thawing. The presented case studies illustrate how seismology can give quantitative insights into material damage and allow separating effects of irreversible damage growth from reversible thermoelastic hydrologic variations. This knowledge is needed to better predict the development of large failures and thus improve warning systems.
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