Inland Migration of Crevasses on the Greenland Ice Sheet

格陵兰冰盖的表面在2012年夏季经历了前所未有的融化，连续十年的夏季融化范围和持续时间都超过了平均水平。在2012年的高峰期间，融化覆盖了约97%的冰盖，持续时间比1979-2011年的平均时间长了近两个月。这种持续加剧的融化导致了地表的下降，并通过提供径流来加速冰流，从而加强冰下滑动。总的来说，在过去十年中，冰盖融化对海平面上升的贡献约占一半。在冰盖上迄今为止没有裂缝的地方出现表面裂缝的报告与加剧的融化相吻合。这些裂缝可以作为地表融水向冰盖床输送的新生通道，这可能促进加速冰流向内陆传播，并可能导致额外的地表裂缝。它们的发生也对安全后勤作业（飞机降落、地面穿越）构成潜在危险。2012年冰川融化高峰期间，格陵兰岛的乌鸦营地出现了裂缝，导致美国军用飞机训练活动暂时停止。格陵兰内陆导线（GrIT）在格陵兰西北部使用的路线上也出现了新的裂缝，可能严重影响未来的穿越活动。人们提出了两种假说来解释裂缝的发生：一种假说认为，雷文地下的铁质含水层突然排水，导致上覆铁质下沉，从而形成裂缝；另一种假设涉及到冰流的下游加速导致应变速率的增加和真正裂缝的形成。如果第二个假设是正确的，那么裂缝的尺寸和发生的频率在未来很可能会增加。这项提案将通过全球定位系统（GPS）对冰的运动和应变率进行调查，并使用非常高分辨率的卫星图像详细评估裂缝随时间的分布，来验证这些假设。为了更好地预测冰盖对未来气候强迫的反应，以及对格陵兰岛的后勤活动做出明智的长期规划决策的能力，需要了解导致新表面裂缝出现的过程，并评估其分布随时间增加的可能性。

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.