Stress Redistribution Explains Anti-correlated Subglacial Pressure Variations
Stress Redistribution Explains Anti-correlated Subglacial Pressure Variations
复制标题
应力重新分布解释了反相关的冰下压力变化
DOI：
--
复制
发表时间：
2018
影响因子：
2.9
通讯作者：
J. Hagen
中科院分区：
文献类型：
--
作者：
P. Lefeuvre;T. Zwinger;M. Jackson;O. Gagliardini;G. Lappegard;J. Hagen
我们使用有限元模型来解释冰川底部的反相关压力变化，以显示基底冰中应力重新分布的重要性。在挪威北部210米厚的engbreen冰川底部，安装了两对测压元件，相距20米。位于其中一对上的冰下通道的加压导致它们之间的压力反相关。利用一个210 m厚、25-200 m宽冰川的完整Stokes三维模型，以及一个以压力边界条件表示的加压冰下通道，研究了河床处的反相关响应。该模型再现了冰川床上的反相关压力响应以及与称重传感器观测值相同数量级的压力变化。反相关模式依赖于河床/地表坡度，当河床坡度为零时，反相关压力变化在距离河道大于10-20米的地方重现，而当河床倾斜5度时，反相关变化发生在距离河道10米的地方。通道的压力导致横向或垂直冰流远离通道，支撑上覆冰并减少床上的正常应力。如果模拟的横截面受到横向约束，且地层平坦，则由此产生的桥接效应将作用在地层上的一些法向力转移到两侧。相反，如果床层是倾斜的，那么通道的支撑只是垂直的。该模型表明，应力重分布的影响取决于冰下通道和冰川的坡度以及几何形状，并且在距离通道相同的距离处可能导致相反的压力响应。
We used a finite element model to interpret anti-correlated pressure variations at the base of a glacier to show the importance of stress redistribution in the basal ice. Two pairs of load cells are installed 20 m apart at the base of the 210 m thick Engabreen glacier in Northern Norway. Pressurisation of a subglacial channel located over one pair led to anti-correlation in pressure between them. A full Stokes 3D model of a 210 m thick and 25-200 m wide glacier with a pressurised subglacial channel represented as a pressure boundary condition was used to investigate the anti-correlated response at the bed. The model reproduced the anti-correlated pressure response at the glacier bed and variations in pressure of the same order of magnitude as the load cell observations. The anti-correlation pattern was shown to depend on the bed/surface slope such that the anti-correlated pressure variations were reproduced at a distance greater than 10-20 m from the channel when the bed slope was zero, whereas anti-correlation occurred within 10 m of the channel when the bed was inclined by 5 degrees. Pressurisation of the channel led to lateral or vertical ice flow away from the channel, support of the overlying ice and reduction of the normal stress on the bed. If the modelled cross-section was laterally constrained and the bed flat, the resulting bridging effect diverted some of the normal forces acting on the bed to the sides. In contrast, if the bed was inclined, then channel support was vertical only. The model showed that the effect of stress redistribution depends on the slope as well as the geometry of the subglacial channel and glacier, and can lead to an opposite response in pressure at the same distance from the channel.