Unveiling the subglacial landscape in the Southern Andes shows an abundance of future glacial lakes

Glaciers in the southern Andes are retreating rapidly because of ongoing climate warming. This process is reshaping the mountainous landscape and promoting the formation of new glacial lakes. Therefore, quantifying glacier ice thickness and subglacial topography is vitally important for assessing future water resources and glacier-retreat hazard. Of particular interest are bed over-deepening that will fill with water once they become ice-free. Such water bodies are potentially trigger sites for devasting Glacial Lake Outburst Floods (GLOF). However, estimates of ice thickness at the regional scale in the southern Andes remain uncertain due to the scarcity of in situ data on current glacier thickness as well as strong climatic and topographic gradients.Here, we present a regional reconstruction of glacier ice thickness and subglacial topography for the entire Southern Andes, systematically constrained by the extensive archive of ground-penetrating radar measurements available for the region. Ice thickness is reconstructed, assuming perfect plasticity. Apart from direct measurements, we use glacier retreat and observe elevation changes to constrain the reconstruction. The resultant thickness map shows latitudinal contrasts in glacier geometry, with thin ice bodies in the desert Andes and substantially thicker ice masses in Patagonia.We estimate a total volume of glacial ice of 5,960.6 km³ in the Southern Andes, equivalent to a global sea-level rise of 15.1 mm, with more than 95% of this volume concentrated in Patagonia, particularly in the two vast icefields there. By removing the modeled ice cover, we determine the subglacial topography and identify more than 6,000 overdeepenings that represent potential sites for future glacial lake formation. For each potential lake, we estimate its area, depth, and volume, yielding a total potential lake volume of approximately 177.6 km³ across the Southern Andes, with most of this volume concentrated in Patagonia (171.18 km³).Our results provide a new measurement-informed, database for assessing future glacier evolution, freshwater storage, and emerging GLOF hazards in the Andes, providing critical information for climate adaptation and risk management in high-mountain regions