Supraglacial streams drive widespread partial-depth hydrofractures in ice sheets

Abstract Dramatic supraglacial lake drainage events in Greenland and Antarctica are enabled by rapid hydrofracture propagation through >1 km ice. Here, we present a slower mode of hydrofracture, where hairline surface fractures intersect supraglacial streams, and hypothesise that fracture penetration depth is critically limited by water supply and englacial refreezing. We apply a model of stream-fed hydrofracture to the Greenland Ice Sheet and find that, under most conditions, 2-cm-wide fractures can penetrate hundreds of metres before freezing closed. Full-depth hydrofracture is more restricted, requiring relatively large meltwater channels and/or warm englacial conditions. Given the abundance of streams and surface fractures across Greenland and Antarctica's expanding ablation zones, stream-driven hydrofractures are likely ubiquitous even where distant from supraglacial lakes and crevasses. While lake-driven hydrofracture is now argued to have minimal long-term dynamic impacts, this intriguing stream-fed hydrofracturing has two important consequences. First, by driving widespread cryohydrologic warming at depths far greater than surface crevassing, it explains a cold bias in modelled englacial thermal profiles. Second, the associated decrease in ice viscosity, and increased damage accumulation, will enhance the vulnerability of ice sheets to dynamic instability under climate warming. This process is likely undetectable by remote sensing, and warrants more detailed modelling and field investigations.