Sliding of till over bedrock: scratching, polishing, comminution and kinematic-wave theory
Sliding of till over bedrock: scratching, polishing, comminution and kinematic-wave theory
复制标题
耕耘机在基岩上的滑动：刮擦、抛光、粉碎和运动波理论
作者：
R. Hindmarsh
观察到的材料被(I)大碎石挖出的划痕和(Ii)碎屑抛光所去除的比率表明，后者是基岩侵蚀的主要形式。我们用冰川碎屑的多阶段分解模型来检验这一点，该模型包括细粉的主动侵蚀。这些模型表明，母体碎屑可以通过其子体碎片的作用，侵蚀数倍于其自身体积的基岩。在基岩上滑动很可能是一个强有力的冲刷来源。通过提出滑动体/基岩滑动律，研究了滑动体的运动学。即使在施加的应力没有纵向梯度的情况下，冰流也会自然地变薄并延伸到覆盖。越厚的耕作覆盖层底部的有效压力越大，滑动速度越低，对于较厚的覆盖层，泥沙通量随厚度的增加而减少。这意味着向后移动的运动学波动和冲击。有人认为，这与鼓石的钝化上游面有关，鼓形作用可能是碎屑滑过基岩的结果。
The observed ratio of removal of material by (i) scratches gouged by large clasts and (ii) polishing by debris suggests that the latter is the dominant form of bedrock erosion. We examine this with a multi-stage breakdown model of glacial debris, which includes active erosion by fines. These models suggest that a mother clast can, through the action of its daughter debris, erode several times its own volume of bedrock. Till-sliding over bedrock is likely to be a potent source of scouring. By proposing a till/bedrock sliding law, we investigate the kinematics of sliding till bodies. Ice flow naturally tends to thin and extend till cover, even in the absence of longitudinal gradients in the applied stress. Thicker till cover has an increased effective pressure at its base, a lower sliding velocity and, for larger thicknesses, a decrease in sediment flux with thickness. This implies backward-moving kinematic waves and shocks. It is suggested that this is related to the blunt upstream faces of drumlins, and that drumlinization can be a consequence of debris sliding over bedrock.