Dynamic response of lake-terminating glaciers to the abrupt drainage of Lago Greve, in the Southern Patagonia Icefield

Abstract. Abrupt drainage of proglacial lakes has the potential to trigger large changes in lake-terminating glaciers. However, observations of glacier response to lake drainage remain sparse. Here, we report changes seen in three glaciers in the Southern Patagonia Icefield (Glaciar Pío XI, Greve, and Lautaro) terminating in a large proglacial lake, which drained, lowering the lake level by ~18 m in 2020. This event provided a rare opportunity for a natural experiment to compare glacier responses to a common lake-level perturbation. Using satellite data from 2017–2021, we investigated the impact of lake drainage on ice-front position, surface elevation, flow speed, and frontal ablation. Glaciar Pío XI decelerated to <10 % of its pre-event speed during the drainage, suggesting the ice-flow influenced by lake level through changes in subglacial water pressure. Glaciar Greve showed speed-up, ice-front advance, and surface lowering, suggesting hydrostatic pressure plays a fundamental role acting on the glacier front. Glaciar Lautaro showed no clear changes attributable to the event. The contrasting responses of these glaciers are likely due to individual settings, i.e., subglacial hydrology, ice thickness, bed geometry, and frontal ablation. Our results provide important implications for glacier and ice sheet response to changes in conditions at glacier fronts.