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研究进展
发布者:江苏省遥感学会秘书处 发布时间:2015/8/19 阅读:1163次 
Greenland supraglacial lake drainages triggered by hydrologically induced basal slip

      在冰面湖底部,水流驱动的裂隙延伸会将大量地表融水迅速带到格陵兰冰盖底部。这种排水活动会导致冰盖出现暂时性的加速移动,并为形成小水沟,成为更多的顶底融水传输通道,在整个融冰季节发挥作用。尽管现已确定,裂缝必须全部注满水才能抵达河床,但其在湖底引起水压裂活动的精确作用机制还尚为人知。本文发现,在格陵兰冰盖西部的一个湖泊中,排水之前会出现6~12小时的冰盖抬升和/或增强的基面滑移作用。通过密集的全球定位系统(Global Positioning System, GPS)网络进行观察,本文确定了2011-2013年间三次快速排水活动之前、之中和之后的冰盖基底融水分布状况,每一次排水都会产生张应力,导致湖底的水压致裂活动增强。本文假设,这些破裂与融雪水通过附近的冰川锅穴系统(moulin system, 连通冰盖表面与底部的垂直通道)流入基底有关。此结果说明,如果湖泊在较少裂缝、水渗透性较差的冰盖中心地带形成,由湖泊排水压裂导致的成冰盖顶底通道的活动就会受到限制。

      Laura A. Stevens; Mark D. Behn; Jeffrey J. McGuire; et al. Water-driven fracture propagation beneath supraglacial lakes rapidly transports large volumes of surface meltwater to the base of the Greenland Ice Sheet1. These drainage events drive transient ice-sheet acceleration and establish conduits for additional surface-to-bed meltwater transport for the remainder of the melt season. Although it is well established that cracks must remain water-filled to propagate to the bed, 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, where water at the bed is currently less pervasive, the creation of new surface-to-bed conduits caused by lake-draining hydro-fractures may be limited.

(来源:Nature, 2015, 522: 73–76 doi:10.1038/nature14480)

 

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