盒61年冰川细沟的形态和冰川磨蚀的推论
艾弗森(1991)使用冰川条纹,最近在碳酸盐岩基岩接触毗邻萨斯喀彻温省的冰川,加拿大,力学的推断冰川磨蚀。艾弗森测量宽度,个人细沟的深度和长度,以及对各种形态的标准。条纹的形状表明,磨损碎片一般旋转。艾弗森定义了三种类型的条纹。1型条纹成为逐步down-glacier更广泛和深入,直到他们突然结束,通常深沟的峭壁。他们推断形式作为纹状碎屑犁向前和向下,之前striator点脱落碎屑或碎屑的扭矩是足够大,这样它旋转槽。2型条纹开始和终止微弱,薄的痕迹。他们不断扩大和深化,直到达到一个最大宽度和深度附近的中心观点。他们可能是由夏普striator点旋转滑动。最初有一个很大的耕作角点,导致进步纹的切口。 Deeper ploughing causes more rapid clast rotation as the torque on the clast increases. Rotation, together with comminution of the clast point, reduces the ploughing angle so that there is a steady reduction in striation depth. Consequently Type 2 striae indicate clasts that slow down until the maximum striation depth is reached and then steadily accelerate, until at the striation terminus, the clast has the same velocity as the ice. Type 3 striae begin abruptly as deep gouges and then become progressively narrower and shallower down-glacier. They are inferred to form where a striator point contacts and indents the bed. Clast rotation with little displacement along the bed produces a low ploughing angle, so that a gradual reduction in indentation depth occurs as sliding proceeds. Overall, the conclusion is that clasts with steep leading edges will abrade progressively deeper into the bed with sliding, whereas those with more gently inclined leading edges will climb out of their grooves. The paper shows how, therefore, glacial striae can be used to make inferences about former subglacial processes.
资料来源:艾弗森,天然橡胶(1991)冰川细沟形态——对冰川床和断层表面的磨损的影响。《美国地质学会通报》,103年,1308 - 16。
条纹的连续性是一个有效的正常压力之间的平衡,使冰川的底部接触的床上,和底水压力的变化,允许小蛀牙形成(见4.6节)。条纹形成了不同的冰流的方向可能是叠加在正交模式(正交条纹;图6.2)。这发生在冰流方向变化时,由于冰的再前进deglaciated区域或由于在冰川冰流的变化方向。正交条纹记录,第二个冰流无法侵蚀早些时候流的所有证据,因为冰川磨蚀的低效率或由于时间不足。可以使用横切条纹的发生,因此,推断前冰川动力学(框6.2)。
继续阅读:62箱使用的冰蚀地形重建冰川动力学
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