Laboratory Studies of Contact Forces Between Basal Clasts and Bedrock

冰川侵蚀最重要的机制可能是采石：冰下基岩裂缝的生长和合并以及由此产生的岩石碎片的移动。虽然有证据表明，侵蚀速率取决于滑动速度，但在冰床分离区，由波动的基础水压引起的床上应力的变化可能会提高基岩内裂缝增长的速率。为了实时研究采石，在挪威斯瓦尔蒂森冰盖的出口冰川engbreen的床上安装了一个12厘米高的花岗岩台阶，其表面有裂缝。当冰从台阶上滑过时，声发射传感器监测到裂缝的增长。同时还测量了台阶背风处的垂直应力、水压和空腔高度。水压是通过把水抽到台阶的底部来控制的。通过反复的泵试验，应力面上的裂缝不断扩大，直到台阶的背风面被采掘，这表明波动的水压导致裂缝扩展所需的应力阈值超过。为了充分理解采石机制，另一项野外工作将测量采石率作为滑动速度的函数，在春季融化季节，滑动速度预计将增加2至3倍。声发射将与滑动速度和自然水压波动相关。结果将允许评估滑动速度和水压变化对采石的相对影响。通过提供冰下岩石裂缝增长的第一次测量，该项目将提供必要的数据，将冰川学变量与采石率联系起来，消除目前存在于基于不确定侵蚀规则的景观演化模型中的模糊性。实地数据将与冰川采石的理论模型相结合。这项工作的高潮将是一个采石规则，可以作为大规模侵蚀模型的基础。

Probably the most important mechanism of glacial erosion is quarrying:the growth and coalescence of cracks in subglacial bedrock anddislodgement of resultant rock fragments. Although evidence indicatesthat erosion rates depend on sliding speed, rates of crack growth inbedrock may be enhanced by changing stresses on the bed caused byfluctuating basal water pressure in zones of ice-bed separation. Tostudy quarrying in real time, a granite step, 12 cm high with a crack inits stoss surface, was installed at the bed of Engabreen, an outletglacier of the Svartisen Ice Cap, Norway. Acoustic-emission sensorsmonitored crack-growth events in the step as ice slid over it. Verticalstresses, water pressure, and cavity height in the lee of the step werealso measured. Water pressure was manipulated by pumping water to thelee of the step. With repeated pump tests, the crack on the stoss facegrew until the step's lee surface was quarried indicating thatfluctuating water pressure caused stress thresholds required for crackgrowth to be exceeded. To fully comprehend quarrying mechanisms, anotherfield effort will measure quarrying rates as a function of sliding speedduring the spring melt season when sliding speed is expected to increaseby a factor of 2 to 3. Acoustic emissions will be correlated to slidingspeed and also to natural water-pressure fluctuations. Results willallow an assessment of the relative effects of sliding speed andwater-pressure variability on quarrying. By providing the firstmeasurements of crack growth in subglacial rock, this project willprovide the necessary data to correlate glaciological variables toquarrying rates, removing the ambiguity that exists presently inlandscape evolution models which are grounded on uncertain erosionrules. The field data will be combined with a theoretical model ofglacial quarrying. The culmination of this work will be a quarrying rulethat can serve as a basis for large-scale erosion models.