Greenland supraglacial lake drainages triggered by hydrologically induced basal slip
Greenland supraglacial lake drainages triggered by hydrologically induced basal slip
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DOI：
10.1038/nature14480
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发表时间：
2015-06-04
期刊：
影响因子：
64.8
通讯作者：
King, Matt A.
中科院分区：
文献类型：
--
作者：
Stevens, Laura A.;Behn, Mark D.;King, Matt A.
冰上湖下的水驱动断裂扩展迅速将大量的表面融水输送到格陵兰冰盖的底部（1）。这些排水事件驱动了瞬时冰盖加速（1-3），并为融化季节剩余时间的额外表面到床融水运输建立了管道（1，4 -6）。虽然已经确定裂缝必须保持充满水才能扩展到河床（7-9），但在湖泊下方引发水力压裂事件的精确机制尚不清楚。在这里，我们表明，在格陵兰岛西部冰盖的湖泊，排水事件之前的6-12小时的冰盖隆起和/或增强的基底滑动。我们从一个密集的全球定位系统（GPS）网络的观测使我们能够确定在2011-2013年的三次快速排水之前，期间和之后冰盖床的融水分布，每次排水都会产生张应力，促进湖底的水力压裂。我们假设，这些前体是与通过邻近的冰川沟系统（连接冰盖的表面和底部的垂直管道）引入融水床。我们的研究结果表明，由于湖泊形成在裂缝较少的冰盖内部区域（10-14），其中床层的水目前不太普遍（5，14 -16），由湖泊排水水力压裂引起的新的表面到床层管道的创建可能是有限的。
Water-driven fracture propagation beneath supraglacial lakes rapidly transports large volumes of surface meltwater to the base of the Greenland Ice Sheet(1). These drainage events drive transient ice-sheet acceleration(1-3) and establish conduits for additional surface-to-bed meltwater transport for the remainder of the melt season(1,4-6). Although it is well established that cracks must remain water-filled to propagate to the bed(7-9), the precise mechanisms that initiate hydro-fracture events beneath lakes are unknown. Here we show that, for a lake on the western Greenland Ice Sheet, drainage events are preceded by a 6-12 hour period of ice-sheet uplift and/or enhanced basal slip. Our observations from a dense Global Positioning System (GPS) network allow us to determine the distribution of meltwater at the ice-sheet bed before, during, and after three rapid drainages in 2011-2013, each of which generates tensile stresses that promote hydro-fracture beneath the lake. We hypothesize that these precursors are associated with the introduction of meltwater to the bed through neighbouring moulin systems (vertical conduits connecting the surface and base of the ice sheet). Our results imply that as lakes form in less crevassed, interior regions of the ice sheet(10-14), where water at the bed is currently less pervasive(5,14-16), the creation of new surface-to-bed conduits caused by lake-draining hydro-fractures may be limited.