Laboratory Simulations Of Glacial Abrasion: Comparison With Theory
Laboratory Simulations Of Glacial Abrasion: Comparison With Theory
复制标题
冰川磨损的实验室模拟：与理论的比较
作者：
N. Iverson
摘要在实验中模拟了冰川磨损，在实验中，一个小的人工冰川床被推到一个固定的冰块下面，并受到压力。实验提供了一种手段，测试磨损的理论模型，特别是那些因素，管理的大小下的应力集中磨损岩石碎片。在初步实验中，研究了垂直冰绕安装在床上的球体的流动。在随后的实验中，大理石板被推到冻结在冰块底部的花岗岩碎片下面。与以前的磨损实验不同，滑动速度是真实的（25 mm d−1），床附近的冰处于压力熔化温度。由此产生的条纹非常类似于在冰川岩床上观察到的条纹。正如Hallet（1979年）所预测的那样，冰向冰床的速度分量对碎片下面的应力有很大影响，经典的回归和蠕变理论提供了碎片上向下拖曳力的近似估计。一半的岩石碎片旋转显着，占10-50%的运动相对于床和影响磨损率和剪切应力支持沿着冰床界面。条纹图案间接表明，碎片旋转抑制冰压力的增加，这可能会增加碎片表面上的粗糙元素的阻力。这可能是由于碎片周围的水膜厚度减少，而水从床中泄漏。
Abstract Glacial abrasion was simulated in experiments in which a small artificial glacier bed was pushed beneath a fixed ice block under pressure. The experiments provide a means of testing theoretical models of abrasion, particularly those factors that govern the magnitude of stress concentrations beneath abrading rock fragments. In preliminary experiments, vertical ice flow around a sphere mounted on the bed was studied. In subsequent experiments, marble tablets were pushed beneath granitic rock fragments frozen into the base of the ice block. Unlike previous abrasion experiments, the sliding velocity was realistic (25 mm d−1), and ice near the bed was at the pressure-melting temperature. Resultant striations closely resemble those observed on glaciated bedrock. As predicted by Hallet (1979), the component of the ice velocity towards the bed strongly influenced stresses beneath fragments, and classical regelation and creep theory provided an approximate estimate of the downward drag force on fragments. Half of the rock fragments rotated significantly, accounting for 10–50% of their motion relative to the bed and influencing abrasion rates and the shear stress supported along the ice-bed interface. Striation patterns indirectly suggest that fragment rotations were inhibited by increases in ice pressure, which presumably increased the drag on roughness elements on fragment surfaces. This may have resulted from a reduction in the thickness of the water film around fragments, facilitated by leakage of water from the bed.