Erosion-driven shrinkage of recently glacier-detached lakes signals a proglacial-to-paraglacial transition across the Third Pole

Glacier retreat drives the expansion of glacier-contact lakes until topographic constraints trigger their detachment from parent glaciers. While the expansion phase is well-documented, the post-detachment evolution and its driving mechanisms remain poorly understood, limiting future glacier-related water resource and hazard assessments. Here, we investigated the spatio-temporal evolution of recently glacier-detached lakes across the Third Pole from 1990 to 2023 by combining multi-temporal lake inventories, climate and glacier mass-balance datasets, glacier runoff simulations, and geomorphic proxies for erosion and sediment supply. We identified 882 glacier-contact lakes that became detached during the study period, equivalent in number to 29% of the 3024 glacier-contact lakes mapped in 2023. Contrary to the widely documented expansion of glacier-contact lakes, detached lakes decreased in total area from 45.11 ± 0.02 to 42.63 ± 0.02 km2, corresponding to an estimated water-volume loss of ∼0.04 Gt, despite an increase in modeled glacier runoff of ∼0.37 Gt. Moraine-dammed lakes accounted for the larger absolute area loss, whereas bedrock-dammed lakes showed greater relative shrinkage. Shrinking detached lakes exhibited a median proglacial erosion potential about two times higher than non-shrinking lakes and preferentially occurred in areas with higher abrasion potential, suggesting an important role of proglacial erosion and sediment infilling in post-detachment lake shrinkage. These results indicate that detached lake evolution cannot be explained by meltwater supply alone. Instead, glacier detachment may mark a shift from meltwater-dominated lake expansion toward sediment-influenced lake shrinkage, reflecting an ongoing proglacial-to-paraglacial transition in high mountain glacial lake systems. Accounting for this transition can improve future assessments of glacial lake evolution, alpine water storage, and GLOF-related hazards under continued glacier retreat.