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：冰下基岩裂缝的增长和合并以及由此产生的岩石碎片的移动。虽然证据表明，侵蚀率取决于滑动速度，在基岩裂缝增长率可能会提高由波动的基底水压力在冰床分离区所造成的床上的应力变化。为了研究真实的采石过程，在挪威斯瓦蒂森冰帽出口冰川恩格森的河床上安装了一个高12厘米、表面有裂缝的花岗岩台阶。当冰滑过台阶时，声发射传感器监测台阶上的裂缝生长情况，同时测量台阶背风处的垂直应力、水压和空腔高度。通过将水泵送到台阶的底部来控制水压。随着反复的泵试验，stoss面上的裂纹不断增长，直到台阶的背风面被采石，这表明波动的水压导致了裂纹增长所需的应力阈值被超过。为了充分理解采石机制，另一个领域的努力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。结果将允许对滑动速度和水压变化对采石的相对影响进行评估。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相关联，消除目前存在于基于不确定侵蚀规则的景观演变模型中的模糊性。现场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.