Potential effects of subglacial water-pressure fluctuations on quarrying
Potential effects of subglacial water-pressure fluctuations on quarrying
复制标题
冰下水压波动对采石的潜在影响
作者：
N. Iverson
摘要冰川下的水压波动可能通过重新分配冰下基岩上的应力和改变基岩裂缝中的水压来加速岩石破裂。为了研究水压波动对冰下基岩断裂的潜在影响，数值模拟了冰流通过一个小基岩台阶，在其背风面有一个充满水的空腔，并计算了基岩表面上的应力作为空腔中瞬态水压的函数。然后，使用床层上的应力来计算台阶内的主应力差。空腔水压的快速降低增加了床层中的主应力差，增加了台阶中裂纹生长的可能性，并形成了主要垂直的裂缝。相对不渗透的基岩可能最容易在水压降低期间发生断裂，因为当洞穴中的水压降低时，岩石内的裂缝中的高水压可以保持。这些结果，当考虑到很大的可能性，增加水压加速从床上松动的岩石碎片的移动，表明在冰床分离的地区，水压波动通常很大，采石率可能高于沿着冰川床的其他部分。
Abstract Water-pressure fluctuations beneath glaciers may accelerate rock fracture by redistributing stresses on subglacial bedrock and changing the pressure of water in bedrock cracks. To study the potential influence of water-pressure fluctuations on the fracture of subglacial bedrock, ice flow over a small bedrock step with a water-filled cavity in its lee is numerically modeled, and stresses on the bedrock surface are calculated as a function of transient water pressures in the cavity. Stresses on the bed are then used to calculate principal stress differences within the step. Rapid reductions in cavity water pressure increase principal stress differences in the bed, increasing the likelihood of crack growth in the step and the formation of predominantly vertical fractures. Relatively impermeable bedrock may be most susceptible to fracturing during water-pressure reductions because high water pressure in cracks within the rock can be maintained, as water pressure decreases in cavities. These results, when considered in conjunction with the strong likelihood that increases in water pressure accelerate the removal of rock fragments loosened from the bed, suggest that in zones of ice-bed separation where water-pressure fluctuations typically are large, rates of quarrying may be higher than along other parts of glacier beds.