Quarrying and abrasion are the two principal processes responsible for glacial erosion of bedrock. The morphologies of glacier hard beds depend on the relative effectiveness of these two processes, as abrasion tends to smooth bedrock surfaces and quarrying tends to roughen them. Here we analyze concentrations of bedrock discontinuities in the Tsanfleuron forefield, Switzerland, to help determine the geologic conditions that favor glacial quarrying over abrasion. Aerial discontinuity concentrations are measured from scaled drone-based photos where fractures and bedding planes in the bedrock are manually mapped. A Tukey honest significant difference test indicates that aerial concentration of bed-normal bedrock discontinuities is not significantly different between quarried and non-quarried areas of the forefield. Thus, an alternative explanation is needed to account for the spatial variability of quarried areas. To investigate the role that bed-parallel discontinuities might play in quarrying, we use a finite element model to simulate bed-normal fracture propagation within a stepped bed with different step heights. Results indicate that higher steps (larger spacing of bed-parallel discontinuities) propagate bed-normal fractures more readily than smaller steps. Thus, the spacing of bed-parallel discontinuities could exert strong control on quarrying by determining the rate that blocks can be loosened from the host rock.

中文翻译：

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将基岩不连续性与冰川采石联系起来

采石和磨蚀是造成基岩冰川侵蚀的两个主要过程。冰川硬床的形态取决于这两个过程的相对有效性，因为磨损会使基岩表面变得光滑，而采石会使它们变得粗糙。在这里，我们分析了瑞士 Tsanfleuron 前场的基岩不连续性浓度，以帮助确定有利于冰川采石而不是磨损的地质条件。空中不连续性浓度是从基于无人机的缩放照片中测量的，其中基岩中的裂缝和层理平面是手动绘制的。Tukey 诚实显着性差异检验表明，在前场采石区和非采石区之间，基层法向基岩间断面的空中浓度没有显着差异。因此，需要另一种解释来解释采石区的空间变异性。为了研究平行床层间断可能在采石中发挥的作用，我们使用有限元模型来模拟具有不同台阶高度的阶梯式床层内的床层法向裂缝扩展​​。结果表明，与较小的台阶相比，较高的台阶（平行床层间断的间距较大）更容易传播与床层正常的裂缝。因此，平行床层间断的间距可以通过确定块体从母岩中松动的速率来对采石施加强有力的控制。我们使用有限元模型来模拟具有不同阶梯高度的阶梯床内的床正常裂缝扩展。结果表明，与较小的台阶相比，较高的台阶（平行床层间断的间距较大）更容易传播与床层正常的裂缝。因此，平行床层间断的间距可以通过确定块体从母岩中松动的速率来对采石施加强有力的控制。我们使用有限元模型来模拟具有不同阶梯高度的阶梯床内的床正常裂缝扩展。结果表明，与较小的台阶相比，较高的台阶（平行床层间断的间距较大）更容易传播与床层正常的裂缝。因此，平行床层间断的间距可以通过确定块体从母岩中松动的速率来对采石施加强有力的控制。