Glacier and Ice Sheet Crevasses: Lifecycles and Mass Balance Implications

Abstract:

Glacier and ice sheet mass balance is determined by climatic surface balance, which is the difference between snowfall and runoff, and ice dynamics, which governs iceberg discharge. Crevasses can influence both the climatic surface balance and ice dynamic components of glacier and ice sheet mass balance. We review the observational evidence for the notion of mutually exclusive “low” and “high” advection crevasse lifecycles. In the low advection lifecycle, crevasses are interpreted to be in highly transient equilibrium with their local stress fields at all times. In the high advection lifecycle, crevasses are interpreted to be out of equilibrium with their local stress fields during advection between upstream opening and downstream closing areas. We suggest that the notion of a high advection lifecycle, typically inferred for transverse crevasses in apparent non-equilibrium with their local stress field, generally results from failure to account for the rotation in crevasse geometry introduced by appreciable local tearing (mode III fracture). We therefore favor the notion that crevasses are always in equilibrium with their local stress field. We also review the observational evidence and theoretical support for ten distinct crevasse-related processes that influence surface mass balance and ice dynamics (see Figure). One of these processes is a crevasse-rheology-deformation feedback, whereby an increase in crevasse extent contributes to enhanced cryo-hydrologic warming and hydraulic weakening, which in turn contributes to an increase in deformational velocity and further increase in crevasse extent. We discuss this potential feedback in the context of recent observations at Jakobshavn Isbrae, West Greenland, as well as in the content of the end-member scenario of thermal-viscous collapse of the Greenland ice sheet.