Collaborative Research: Toward an Erosion Rule for Glacial Quarrying: Modeling and Measurements

对冰川采石场侵蚀规律的合作研究：建模和测量爱荷华州立大学（Iowa State university）威斯康星地质调查局（Wisconsin Geological survey）摘要冰川对岩石的侵蚀形成了壮观的地貌，如角状山峰和u形山谷，并可能对山带的岩石隆升速度产生巨大影响，以及与之相关的风化速率、二氧化碳产量和气候变化。采石，即冰川使下垫岩石破裂并移除由此产生的岩石碎片的过程，被认为是冰川侵蚀最重要的过程。然而，目前还没有一个综合性的采石定量模型，将冰川变量（如滑动速度和基础水压）与采石率完全联系起来。因此，在广泛地区（如山带）和较长时期（10^5-10^6年）应用的冰川侵蚀模式的结果在数量上和概念上都是不确定的。通过这项研究，将构建一个多功能的采石理论模型，然后对其进行测试，既可以实时测量冰川下基岩的裂缝生长，也可以绘制最近因冰川退缩而暴露的基岩的裂缝模式。冰流将在由倾斜台阶组成的基岩上建模，在稳定和瞬态情况下，这些台阶背风处的空腔内的水压与滑动速度和空腔大小完全耦合。结果将用于计算岩床中的应力分布以及随之而来的裂缝速度和路径，因为它们缓慢地扩展并隔离可以被冰川轻松提取的岩石块。该模型将通过在挪威北部温带冰川Engabreen的210米滑动冰层下安装倾斜的岩石台阶来进行测试，Svartisen冰河学观测站为人类提供了通往冰川-岩石界面的通道。台阶裂缝增长产生的声波将用于确定冰川学变量与台阶裂缝增长速度和路径之间的关系。为了进一步测试采石模型的各个方面，将在阿尔伯塔省Castelguard冰川前的阶梯基岩上绘制前冰下空洞的大小以及相关冰川诱发裂缝的分布和方向，并与模型预测进行比较。这项工作的总体结果将是一个采石规则，可以作为大规模冰川侵蚀模型的基础。

Collaborative research toward an erosion rule for glacial quarrying: Modeling and measurementsDenis Cohen and Neal Iverson EAR-0229692 Iowa State UniversityThomas Hooyer EAR-0229526 Wisconsin Geological SurveyAbstractErosion of rock by glaciers results in spectacular landforms, such as horn peaks and U-shaped valleys, and can also have a dramatic effect on rates of rock uplift in mountain belts and associated changes in weathering rates, CO2 production, and climate. Quarrying, the process in which glaciers crack underlying rock and remove resultant rock fragments is thought to be the most important process of glacial erosion. There is at present, however, no comprehensive quantitative model of quarrying that fully links glaciological variables, such as sliding speed and basal water pressure, to quarrying rate. Thus, results of models of glacial erosion applied over broad areas (e.g., mountain belts) and long periods (10^5-10^6 years) are uncertain, both quantitatively and conceptually.With this research, a versatile theoretical model of quarrying will be constructed and then tested, both with real-time measurements of crack growth in bedrock beneath a glacier and with mapping of crack patterns in bedrock recently exposed by glacier retreat. Ice flow will be modeled over bedrock consisting of inclined steps by fully coupling water pressure in cavities in the lee of these steps with sliding speed and cavity size for both steady and transient cases. Results will be used to calculate the stress distribution in the rock bed and the consequent speeds and paths of cracks, as they slowly extend and isolate rock blocks that can be extracted easily by the glacier. The model will be tested by installing inclined rock steps beneath 210 m of sliding ice at Engabreen, a temperate glacier in northern Norway, where the Svartisen Glaciological Observatory provides human access to the glacier-rock interface. Sound waves generated by growth of cracks in the steps will be used to determine the relation between glaciological variables and crack-growth speeds and paths in the steps. To further test aspects of the quarrying model, sizes of former subglacial cavities and distributions and orientations of associated glacially-induced cracks will be mapped on stepped bedrock in front of Castelguard Glacier, Alberta, and compared with model predictions. The overall result of this work will be a quarrying rule that can serve as the basis for large-scale models of glacial erosion.