Megalandslides and deglaciation: modelling of two case studies in the Central Andes

Abstract

Large-volume rock slope failures are one of the main hazards in high mountain glaciated valleys, inducing severe damage to population and infrastructure, representing a high risk for society, ecosystems and infrastructure. The Andes Mountain Range is shaped by glacial activity and therefore by megalandslides due to changes in shear strength and deformation during periods of glaciation and deglaciation, which modify the slope stress state and, along with other processes, induce progressive damage in the rock mass, eventually leading to failure. The study focuses on validating the hypothesis that glacier unloading contributes to these types of landslides. The research numerically modelled the effects of glacier unloading on stress distribution and its potential impact on landslides, particularly using two Chilean cases: The 1987 Estero Parraguirre and the 2018 Yerba Loca rock slides. These models used the Universal Distinct Element Code, along with geological and geotechnical data from previous studies and field observations. The numerical results showed that the combination of shear stress changes due to glacial unloading and structural control from main discontinuities could cause landslides, with the deglaciation of glaciers potentially preparing the slope for catastrophic failure that may occur due to external climatic or tectonic triggers. The results suggest that stress redistribution and damage to the rock mass caused by deglaciation can lead to progressive failure. Further work is needed to understand better the slope failure mechanics to assess the geohazards in the Andes and other mountain regions.