Tracking the Movement and Spatial Patterns of High-elevation Crevasses in the Interior of the Greenland Ice Sheet.

Abstract:

Surface meltwater at high elevations of Greenland is likely to influence ice dynamics only if water finds paths to the englacial and subglacial system. Despite lakes forming higher on the ice surface, crevasses and moulins have been considered unlikely to form above 1600 m above sea level (asl) in southwest Greenland, limiting the elevation at which lakes could hydrofracture to the bed and influence ice dynamics. However, in 2012, substantial snowmelt exposed over one thousand narrow surface cracks up to 1900 m asl in southwest Greenland, with reports of individual cracks as high as 2100 m. Some of the cracks are found to be adjacent to meltwater lakes that have formed at these elevations in just the past 20 years. In this study we use satellite imagery, digital elevation models, and data from GPS stations installed among a field of crevasses near the KAN_U field site, to gain insight into local ice dynamics and the formation and behavior of high-elevation crevasses in the interior of the Greenland ice sheet. Five GPS stations at 1860 m asl installed for one year show accelerating ice flow with annual speeds now exceeding 55 m yr^-1, a 7.5% increase since 2009. Longitudinal strain rates are ~0.1% yr^-1, considerably less than the 0.5% yr^-1 critical strain rate thought to initiate crevassing in Greenland. Crevasses aligned strongly with local topography and occurred more frequently in areas with a steeper slope. This suggests that recent near-surface ice formation may reduce the strain needed to cause fracture propagation within the firn layer, increasing the elevation limit at which crevasses form in Greenland, with potential implication for high-elevation dynamic feedbacks.