Stability of Moraine and Rock Slopes at Glacial Lakes—Two Case Studies in the Cordillera Blanca

Two presented cases of slope-specific stability assessment illustrate an approach of low-impact investigation techniques, which at the same time allow obtaining necessary data for reliable and realistic slope stability calculations. The applied methods combine field geomorphological, structural and engineering geological investigations with basic laboratory rock and soil tests to constrain the strength properties of the soil, rock discontinuities and rock mass forming landslide material and determining its initiation. Careful observations of the slope’s natural conditions served as input data and along with available historical information about sliding frequencies were used to validate the results of the slope stability calculations. For the investigated cases, they show that glacier retreat and thinning were necessary, but not sufficient conditions for landslide initiation in both, a moraine and a rock slope. Other factors need to contribute to low slope stability and material strength to allow failure initiation. These are water saturation of both, soils and rocks within a slope, seismicity, favorable slope dips and structural conditions, and long-term rock strength deterioration, which is probably one of the factors resulting in delayed rock slope response to deglaciation. At higher altitudes, climate-induced permafrost degradation has the potential significantly contribute to long-term slope destabilization.