Laboratory Studies of Contact Forces Between Basal Clasts and Bedrock

基底碎屑与基岩接触力的室内研究

• 批准号: 0615781
• 负责人: Denis Cohen-corticchiato
• 金额: $ 13.87万
• 依托单位: Iowa State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-10-01 至 2012-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0615781&HistoricalAwards=false
• 关键词: Laboratory; Studies; Contact; Forces; Between

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.

冰川侵蚀的最重要机制可能是采石：冰川下基岩中的裂缝的生长和合并，并在产生的岩石碎片中脱落。尽管证据表明侵蚀速率取决于滑动速度，但床上的裂缝生长速率可能会通过床上造成的压力变化而增加，导致冰床分离区域的基础水压造成的压力。 Tostudy实时采石，在挪威的Svartisen冰盖的登机口（Engabreen）的床上安装了一个花岗岩台阶，高12厘米高，高12厘米，带有裂缝的缝隙。当冰滑过它时，声发射传感器对裂纹生长事件进行了对象。垂直压力，水压和空腔高度测量了阶梯的lee。通过将水抽到台阶的Thelee来操纵水压。通过重复的泵测试，塞子的裂缝在台阶的Lee表面进行划线之前，表明弹性的水压会导致超过裂纹所需的应力阈值。为了完全理解采石机制，另一个场地的努力将测量采石速率，这是在滑动熔体季节的滑动速度的函数，而滑动速度预计将增加2到3倍。声学排放将与滑动速度相关，并且与自然的浇水波动相关。结果将评估滑动速度和水压变异性对采石的相对影响。通过提供裂纹岩石裂纹生长的首先测量，该项目将提供必要的数据，以将冰川变量相关联，从而消除了目前存在于Inlandscape Evolution模型的歧义，这些模型基于不确定的侵蚀性。现场数据将与冰川采石的理论模型结合使用。这项工作的高潮将是采石规则可以作为大规模侵蚀模型的基础。