Large Volcanic Landslides on the Southern Patagonian Icefield and Linkages to Glacial Retreat

Unloading associated with ice-sheet thinning and volcanic-cone collapse can drive larger and more frequent eruptions. The Southern Patagonian Icefield (SPI) is the Southern hemisphere's largest ice mass outside of Antarctica and hosts three active volcanoes. All three (Reclus, Aguilera and Lautaro) have erupted during the Holocene, including several 20th-century eruptions recorded in nearby lake deposits (Stern., 2008, Mayr et al., 2019). This suggests that the volcanoes are likely underlain by active magmatic plumbing systems and responsive to variations in overburden pressure. Warming climates have caused many of the SPI's glaciers to thin and retreat at increased rates recently (Davies and Glasser, 2012), with an ice loss rate calculated at 23.5 ± 8.1 Gt/yr during the period 2002-2016 (Li et al., 2018). This ice loss has the potential to directly influence magma plumbing systems through depressurization, and indirectly influence them by debuttressing hillslopes and triggering landslides, further reducing overburden pressure on the magma chambers.

We identified a series of large debris avalanches from the volcanoes, suggesting that previously stable slopes have been disrupted. Two large (1-5 km²) avalanches occurred on the north flank of Reclus over the last two and a half years, and one 12 km² avalanche occurred on the north flank of Lautaro earlier this year. Here we present a detailed description of the conditions preceding each collapse, and the properties of each collapse. The Reclus collapses are inferred to have been mostly unconsolidated rock, with moderate to low cohesion. The 2019 collapse was the larger of the two and settled onto Amalia glacier, causing local speedup and slowdown, possibly due to the loading of the ice. The Lautaro collapse is found to have a large ice component, and very low cohesion. These large debris avalanches may increase the rate of decrease of overburden pressure on these volcanic plumbing systems, and increased monitoring efforts are necessary to quantify the magnitude of this effect.