Interseasonal persistence of large subglacial channel on Hintereisferner, Austria.

Understanding the subglacial hydrology of glaciers is key in adequately modelling ice flow and future retreat of glaciers under climate change. Subglacial drainage systems are observed and modelled to change with the seasons, varying between an inefficient, distributed drainage system in winter and an efficient, channelised drainage system during the melt season. This directly influences a glacier’s basal flow velocity. Subglacial channels close at the end of the melt season by ice creep and the decrease of melt reducing subglacial discharge, and are typically supposed to disappear completely on many Alpine glaciers before the start of the next melt season. We modelled the evolution of the subglacial discharge system over the course of a year on Hintereisferner, Austrian Alps, using the Glacier Drainage System model (GlaDS). Additionally, we did three ground-penetrating radar (GPR) acquisitions of the glacier tongue over the course of a year (April 2025-March 2026). In both winter and summer acquisitions, en- and subglacial channels could be observed. Besides minor changes in the drainage system, a large subglacial channel was repeatedly detected, indicating possible long-term persistence of channelised drainage throughout the winter despite the expected shutdown of the efficient subglacial drainage system. We present our observations and compare them to the model results. Furthermore, the implications for ice flow and glacier evolution are discussed.