Widespread partial-depth hydrofractures in ice sheets driven by supraglacial streams

Dramatic supraglacial lake drainage events in Greenland and Antarctica are enabled by rapid hydrofracture propagation through ice over 1 km thick. Here we present a slower mode of hydrofracture, where hairline surface fractures intersect supraglacial streams, and hypothesize that penetration depth is critically limited by water supply and englacial refreezing. We develop a model of stream-fed hydrofracture, and find that under most conditions in Greenland, 2-cm-wide fractures can penetrate hundreds of metres before freezing closed. Conditions for full-depth hydrofracture are more restricted, requiring larger meltwater channels and/or warm englacial conditions. Given the abundance of streams and surface fractures across Greenland and Antarctica's expanding ablation zones, we propose that stream-driven hydrofractures are ubiquitous—even where distant from supraglacial lakes and crevasse fields. This intriguing process remains undetectable by current satellite remote sensing, yet has two major impacts that warrant further investigation. First, by driving widespread cryohydrologic warming at depths far greater than surface crevassing, it explains a consistent cold bias in modelled englacial thermal profiles. Second, the associated reduction in ice viscosity and increased damage accumulation act to enhance the vulnerability of ice sheets and shelves to dynamic instability as supraglacial drainage networks expand inland to higher elevations.