On the dark side: Exploring hidden boundaries of glaciers and ice sheets

The glacier surface forms a vital boundary where snow and ice mass exchange occurs through climatic processes. In addition to the visible upper surface, glaciers are bounded by other interfaces, including the underlying base of bedrock/sediment, the front of a calving glacier facing an ocean or lake, and the ice-shelf base in contact with sub-shelf seawater. These unseen boundaries are venues of glacial sliding, hydrology, calving and underwater melting, which play critical roles in glacier dynamics and mass change. These processes are also essential for understanding how glaciers affect surrounding environments through erosion, sedimentation, ice and meltwater discharge. Despite their importance, these boundaries are largely unexplored, in contrast to the increasing amount of data available on the glacier surface. As they are covered by ice and water, special techniques and tools are required for direct observation. For example, hot-water drilling and borehole measurements provide crucial information regarding subglacial processes, and in-situ observations of the ice-water interface can be carried out with uncrewed vehicles or underwater survey devices near the calving front. Based on our experiences in the Alps, Patagonia, Greenland and Antarctica, this presentation highlights the importance of the processes taking place at the hidden glacier boundaries.