Ice-shelf fracture due to viscoelastic flexure stress induced by fill/drain cycles of supraglacial lakes
Ice-shelf fracture due to viscoelastic flexure stress induced by fill/drain cycles of supraglacial lakes
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DOI：
10.1017/s0954102015000292
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发表时间：
2015-12-01
影响因子：
1.6
通讯作者：
Macayeal, Douglas R.
中科院分区：
文献类型：
--
作者：
Banwell, Alison F.;Macayeal, Douglas R.
使用先前导出的浮冰架粘弹性弯曲处理方法，我们模拟了一个轴对称的冰川上湖在遭受年度填/泄循环时的多年演变。我们的粘弹性处理遵循众所周知的薄梁薄板分析的假设，但至关重要的是，也涵盖了幂律蠕变流变学。由于冰架表面在1年的填/排循环后并没有完全恢复到原来的位置，因此湖盆随着每一个连续的循环而加深。当考虑湖底消融时，这一加深过程被显著放大。我们评估了一个典型湖泊达到足够深度的时间尺度，使得冰架断裂可以在湖泊本身之外发生，以响应湖泊填充/排水。我们表明，尽管在一次填充/排水循环中不太可能发生这种情况，但假设地表融水的可用性是无限的，多年后破裂是可能的。这一延伸的潜在裂缝区域意味着，单个湖泊填充/排水事件所产生的弯曲应力可能导致邻近湖泊排水，进而导致更远的湖泊排水。这种自我刺激的行为可能是导致2002年拉尔森B冰架破裂的断裂系统突然广泛出现的原因。
Using a previously derived treatment of viscoelastic flexure of floating ice shelves, we simulated multiple years of evolution of a single, axisymmetric supraglacial lake when it is subjected to annual fill/drain cycles. Our viscoelastic treatment follows the assumptions of the well-known thin-beam and thin-plate analysis but, crucially, also covers power-law creep rheology. As the ice-shelf surface does not completely return to its un-flexed position after a 1-year fill/drain cycle, the lake basin deepens with each successive cycle. This deepening process is significantly amplified when lake-bottom ablation is taken into account. We evaluate the timescale over which a typical lake reaches a sufficient depth such that ice-shelf fracture can occur well beyond the lake itself in response to lake filling/drainage. We show that, although this is unlikely during one fill/drain cycle, fracture is possible after multiple years assuming surface meltwater availability is unlimited. This extended zone of potential fracture implies that flexural stresses in response to a single lake filling/drainage event can cause neighbouring lakes to drain, which, in turn, can cause lakes farther afield to drain. Such self-stimulating behaviour may have accounted for the sudden, widespread appearance of a fracture system that drove the Larsen B Ice Shelf to break-up in 2002.