Monitoring the physical processes driving the mass loss of Tapado Glacier, Desert Andes of Chile

Tapado Glacier (30.15°S, 69.93°W) is a 1.6 km2 ice mass located at high-altitude in Chile’s Desert Andes. This region reaches up to 6000 m a.s.l. and is characterised by high solar radiation and scarce and episodic precipitation. Despite its relatively small size, the glacier extends from 4500 to 5500 m a.s.l and contains several types of surfaces and features, such as a debris-covered section populated by ice cliffs and supraglacial ponds, a field of large snow and ice penitentes, a steep section with crevasses and seracs, and wind-exposed upper areas with minimal snow accumulation. As the ablation and evolution of these elements depend on several physical processes occurring at different rates, monitoring and modelling changes on Tapado Glacier is challenging. Our study describes and quantifies the main glacier changes over the last five years amidst rising summer temperatures and below-average precipitation from a process perspective. Monitoring techniques include direct mass balance and surface geometry measurements, flights of uncrewed aerial vehicles (UAVs), geophysical methods, satellite products, terrestrial LiDAR and automatic cameras. Enhanced melt at ice cliffs and supraglacial ponds primarily drives ablation in the debris-covered section. Ice cliffs and ponds have persisted on the glacier surface since at least 1955. Satellite products and photogrammetrically derived Digital Elevation Models (DEMs) from UAV flights in the period 2020-2023 show that the ablation over a selected cliff and pond was about 10 times higher than over the rest of the debris-covered section. Analysis of historical satellite imagery tracks the evolution of the selected cliff from its formation between 1978 and 2000 to its recent disappearance in 2023, which was corroborated by an automatic camera. Geophysical measurements suggest the presence of ancient supraglacial lakes within the debris cover. The debris-free section shows consistent patterns of thinning and increasing surface roughness. Terrestrial LiDAR indicates an annual surface lowering of about −0.4 m, while UAV flights and direct observations show that the end-of-summer height of penitentes has increased from 1-2 m to more than 2 m, reaching up to almost 6 m in spots. In the upper parts of the glacier, we have observed increasing instability from a serac that produces frequent ice and rock falls into the penitentes-covered area. Summer ablation at the top of the glacier, mainly by sublimation, varied from 0.15 to 1.15 m during 2021-2023. Using recent data from ablation stakes and UAVs, we estimate a summer glacier mass balance of about −0.8 m w.e., which is equivalent to 1.3 million m3 of water. Tapado Glacier exemplifies how different physical processes can drive glacier mass loss and runoff contribution. Recent changes in the glacier have made the field monitoring difficult and pose interesting challenges for glacier modelling.