Evolution of the caldera-filling glacier at Volcán Sollipulli, Chile

In the Southern Volcanic Zone of the Andes (~33°S - ~46°S), glaciers occur only on the highest peaks of active volcanoes. Many of these glaciers, hence, are located within craters or calderas that have a bowl-shaped basal geometry atypical to other mountain glaciers. Volcán Sollipulli, located at about 39° S, hosts a massive glacier that fills a caldera (diameter of ~4 km), with a relatively flat surface elevation of ~2060 m in 2023/2024. Ground-penetrating radar data from 2013 suggested a maximum ice thickness of approximately 750 m, making it the deepest measured body of ice in Chile, north of the Patagonian Ice Fields, thus harboring a vast amount of freshwater. Glaciers in the southern Andes are undergoing unabated retreat, resulting in reduced freshwater storage, increasing contribution to sea-level rise, and leading to the formation of glacial lakes, which implies the potential risk of glacial lake outburst floods (GLOFs).

We present a glaciological study of the caldera Sollipulli glacier, investigating the glacier surface elevation over the last decades using remote sensing data and field measurements, and discuss potential effects of the atypical geometry on its future evolution. While the glacier was already losing mass in the 2000 – 2015 period, our results show a nearly two-fold increase in melt rates since then, resulting in more than 60-m glacier thinning during the 21st century. The increasing melt coincides with observations of late summer snow absence on the entire glacier. This indicates that the freezing level has risen above the maximum glacier surface altitude, leading to shrinkage of the accumulation zone to a minimum or its disappearance. In consequence, the surface-lowering induced melt-elevation feedback is now further enhancing mass loss, in addition to the increased climate forcing. The evolution of existing and new marginal glacial lakes is providing hints on glacier hydrology and provides insights on the potential future lake formation that could affect the glacier’s role as a freshwater reservoir and GLOF risk.