Large landslides cluster along Patagonian Ice Sheet margin

Deglaciation of mountain ranges promotes landslides of various scales and types, and many of them may present a major hazard. Traditionally, it is assumed that landslides are concentrated in the steepest, wettest, and most tectonically active parts of the orogens, where glaciers reached their greatest thickness. Based on our mapping of large landslides (>1km²) over an extensively large area of Southern Patagonia (~305,000 km²), we show that the distribution of landslides can have the opposite trend. The largest landslides within the limits of the former Patagonian Ice Sheet (PIS) cluster along its eastern margins occupying lower, tectonically less active, and arid part of the Patagonian Andes. In contrast to the heavily glaciated, highest elevations of the mountain range, the peripheral regions have been glaciated only episodically. However, a combination of glaciation, weak volcanic and sedimentary rocks, sufficient relief, and presence of large glacial lakes in the past, created favourable conditions for huge number of large landslides along eastern margin of PIS. We explain the scarcity of large landslides in the highest parts of the PIS by presence of strong granitic rocks and long-term glacial modification, that adjusted topography for efficient ice discharge. Our model is applicable only for large bedrock landslides, not for shallow slides and rock falls, which are abundant in the highest and western part of the Andes.