Repeat Subglacial Lake Drainage and Filling beneath Thwaites Glacier

Active subglacial lakes have been identified throughout Antarctica, offering a window into subglacial environments and their impact on ice sheet mass balance. Here we use high‐resolution altimetry measurements from 2010 to 2019 to show that a lake system under the Thwaites glacier undertook a large episode of activity in 2017, only four years after the system underwent a substantial drainage event. Our observations suggest significant modifications of the drainage system between the two events, with 2017 experiencing greater upstream discharge, faster lake‐to‐lake connectivity, and the transfer of water within a closed system. Measured rates of lake recharge during the inter‐drainage period are 137% larger than modelled estimates, suggesting processes that drive subglacial meltwater production, such as geothermal heat flux or basal friction, are currently underestimated.