Inland Migration of Crevasses on the Greenland Ice Sheet

University Of Maine, Orono ME

Investigators

Abstract

The surface of the Greenland Ice Sheet experienced unprecedented melting during the 2012 summer, capping a decade of summers with above average melt extent and duration. Melting covered ~97% of the ice sheet during its 2012 peak and lasted almost two months longer than the 1979-2011 average. This sustained intensified melt has led to down-wasting of the surface, and has also played a role in accelerated ice flow by supplying runoff to enhance subglacial sliding. Altogether, melting has accounted for about half of the ice sheet's increased contribution to sea level rise in the last decade. Reports of surface cracks appearing at hitherto crevasse-free locations on the ice sheet have coincided with the intensified melt. These cracks can act as nascent pathways for the delivery of surface meltwater to the ice sheet bed, which might promote the inland propagation of accelerated ice flow and may lead to additional surface cracking. Their occurrence also constitutes a potential hazard to safe logistic operations (aircraft landing, surface traversing). Cracks appeared at Raven Camp, Greenland, during the peak melt event in 2012 and led to a temporary halt in U.S. military aircraft training activities. New cracks also appeared on the route used by the Greenland Inland Traverse (GrIT) in northwest Greenland and may severely impact future traversing activities. Two hypotheses have been proposed to explain the occurrence of the cracks: one invokes the sudden drainage of a firn aquifer beneath Raven and the resulting subsidence of the overlying firn to form the cracks; the other hypothesis involves the downstream acceleration of ice flow leading to an increase in strain rates and the formation of true crevasses. If the second hypothesis is correct, crack sizes and their frequency of occurrence are likely to increase in the future. This proposal will test those hypotheses by carrying out global positioning system (GPS) surveys of ice motion and strain rate, and a detailed assessment of crevasse distributions through time using very high-resolution satellite imagery. Improved predictions of the ice sheet's response to future climate forcings as well as the ability to make informed long-term planning decisions about logistic activities in Greenland require an understanding of the processes responsible for the appearance of new surface cracks and an assessment of the likelihood that their distribution will increase with time.