Ice flow dynamics forced by water pressure variations in subglacial granular beds
Ice flow dynamics forced by water pressure variations in subglacial granular beds
复制标题
冰下颗粒床中水压变化所迫使的冰流动力学
DOI：
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发表时间：
2016
期刊：
影响因子：
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通讯作者：
M. Siegfried
中科院分区：
文献类型：
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作者：
A. Damsgaard;D. Egholm;L. Beem;S. Tulaczyk;N. K. Larsen;J. Piotrowski;M. Siegfried
冰川和冰流可以通过使下面的水饱和沉积物变形而移动，这些材料的非线性力学通常被认为是快速流动的冰流开始、持续和停止的主要原因。现有的模型未能完全解释驱动从稳定到滑动转变的内部机械过程。我们进行了计算实验，展示了颗粒沉积物内承重力链的重排如何驱动机械转变。孔隙水压力的周期性变化在低于破坏点的应力水平下引起速率相关的蠕变运动，而力链网络的破坏在其上方引起快速的速率无关的流动。这一发现与以往冰下沉积力学的描述形成了对比，后者要么假设速率相关而不管力学状态，要么假设在沉积屈服点之前是无条件稳定的。我们新的微力学计算方法能够再现这两个端元模型之间的重要过渡，并可以解释在冰川，滑坡和缓慢移动的震颤区观察到的多模态速度模式。
Glaciers and ice streams can move by deforming underlying water‐saturated sediments, and the nonlinear mechanics of these materials are often invoked as the main reason for initiation, persistence, and shutdown of fast‐flowing ice streams. Existing models have failed to fully explain the internal mechanical processes driving transitions from stability to slip. We performed computational experiments that show how rearrangements of load‐bearing force chains within the granular sediments drive the mechanical transitions. Cyclic variations in pore water pressure give rise to rate‐dependent creeping motion at stress levels below the point of failure, while disruption of the force chain network induces fast rate‐independent flow above it. This finding contrasts previous descriptions of subglacial sediment mechanics, which either assume rate dependence regardless of mechanical state or unconditional stability before the sediment yield point. Our new micromechanical computational approach is capable of reproducing important transitions between these two end‐member models and can explain multimodal velocity patterns observed in glaciers, landslides, and slow‐moving tremor zones.