Review article: The hydrology of debris-covered glaciers – state of the science and future research directions

Debris-covered glaciers (DCGs) are characterised by distinct hydrological systems that differ fundamentally from those observed on clean-ice valley glaciers. To date, most studies of DCG hydrology have focused on supraglacial hydrology, given that surface streams are broadly accessible and repeat observations can lead to conceptual models of channel evolution. Few have characterised englacial conduits and their layout, and none have directly investigated potential subglacial drainage networks in any setting. In this review, we summarise the current state of knowledge relating to DCG hydrology with a global focus, and present our own field observations to illustrate the distinct nature of DCG landforms on a receding high-elevation glacier in the Himalaya. We draw on recent work that has gone some way towards providing a process-based understanding of the formation and evolution of englacial and subglacial hydrological pathways and consider the role that DCG hydrology plays in regulating water supplies to downstream communities, contrasting this information with clean-ice examples. We conclude by identifying important knowledge gaps that might be considered priorities for future research into DCG hydrology.