AN EXPERIMENTAL STUDY OF GLACIER SLIP OVER HARD AND SOFT BEDS

随着气候变暖，冰川和冰盖的移动影响其稳定性和随之而来的海平面上升。此外，更新世期间的冰盖运动在地貌上留下了壮观的印记。冰川移动最快，改变地貌最严重，主要是通过滑过岩石（硬）或沉积物（软）床移动。在过去的半个世纪里，人们提出了越来越复杂的关于这种滑动的理论，但这些理论基本上没有经过检验，因为冰川床难以进入，而且那里的条件在空间和时间上都是可变的。该项目的目的是使用一个新建造的实验室装置来研究冰川滑动速度、基底阻力（滑动阻力）和有效压力（冰压减去河床水压）之间的关系。该装置拖动一个融化的冰环（外径0.9米，宽0.2米，厚0.15米）穿过硬床或软床。该装置的特点包括无限的滑动位移，温度控制在百分之几度，并连续观察冰滑动和流动分离的床。一组实验将检验这样的理论，即随着滑移速度的增加，粗糙硬床上的稳定阻力达到最大值，然后根据床的几何形状保持不变或减小。底阻力，滑移速度，和有效的压力将分别变化在冰的滑动在其融化温度超过阶梯形和正弦形的床面。在实验的几何约束下的冰流的数值模拟将允许理论结果直接与实验数据进行比较。第二组实验将提供滑动速度、阻力和软床有效压力之间的关系。这些实验还将揭示冰通过融化和再冻结侵入软床孔隙空间的程度，以及软床变形以适应滑动的程度。评估冰川沉积物输送的核心问题。需要强大的冰川滑动定量模型来预测冰川和冰盖的速度。人们观察到冰川涌动，即以异常高的速度向前移动，并以不同的速度后退，显然是对气候变化的反应。该项目的实验研究将以一种无法通过实地观察确定的方式研究冰川运动。 对滑动过程进行更全面的分析将使冰川滑动在冰川和冰盖运动的计算机模型中得到更准确、更少的随意性。这将有助于更好地描述近期的环境变化和遥远过去的地貌演变。

Movement of glaciers and ice sheets affects their stability and attendant sea-level rise as the climate warms. In addition, ice-sheet movement during the Pleistocene left a spectacular imprint on landscapes. Glaciers that move fastest and modify landscapes most severely move primarily by slip over their rock (hard) or sediment (soft) beds. Increasingly sophisticated theories of this slip have been advanced over the last half-century, but these theories are largely untested, owing to the inaccessibility of glacier beds and the spatial and temporal variability of conditions there. The objective of this project is to use a newly constructed laboratory device to study relationships among glacier slip velocity, basal drag (slip resistance) and effective pressure (ice pressure minus water pressure at the bed). The device drags a ring of melting ice (0.9 m outside diameter, 0.2 m wide, 0.15 m thick) across a hard or soft bed. Features of the device include unlimited slip displacement, temperature control to a few hundredths of degree, and continuous observation of ice sliding and flow separation at the bed. One set of experiments will test the theory that as slip velocity increases, steady drag on a rough, hard bed attains a maximum value and then either remains constant or decreases, depending upon the bed geometry. Basal drag, slip velocity, and effective pressure will be individually varied during slip of ice at its melting temperature over stepped and sinusoidal bed surfaces. Numerical modeling of ice flow under the geometric constraints of the experiment will allow theoretical results to be compared directly with experimental data. A second set of experiments will provide relationships among slip velocity, drag, and effective pressure for soft beds. These experiments will also reveal both the extent to which ice invades the pore spaces of soft beds by melting and refreezing and the degree to which soft beds deform to accommodate slip?problems central to evaluating sediment transport by glaciers. Robust quantitative models of glacier slip are needed to forecast the speeds of glaciers and ice sheets. Glaciers have been observed surging, i.e. moving forward at unusually high velocities, and retreating at various rates, apparently in response to changing climate. The experimental studies of this project will examine glacier movement in a a way that can not be determined from field observations. A more complete analysis of the sliding process will allow glacier slip to be treated more accurately and less arbitrarily in computer models of glacier and ice-sheet motion. This will permit better characterizations of environmental change in the near future and of landscape evolution in the distant past.