AN EXPERIMENTAL STUDY OF GLACIER SLIP OVER HARD AND SOFT BEDS

硬床和软床冰川滑移的实验研究

• 批准号: 1023586
• 负责人: Neal Iverson
• 金额: $ 39.04万
• 依托单位: Iowa State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-07-15 至 2016-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1023586&HistoricalAwards=false
• 关键词: EXPERIMENTAL; STUDY; GLACIER; SLIP; OVER

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.

随着气候变暖，冰川和冰盖的运动会影响其稳定性以及随之而来的海平面上升。此外，更新世期间的冰盖运动在景观上留下了壮观的印记。移动最快、对景观影响最严重的冰川主要通过在岩石（硬）或沉积物（软）床上滑动来移动。在过去的半个世纪中，人们提出了越来越复杂的关于这种滑动的理论，但由于冰川床难以接近以及那里条件的时空变化，这些理论基本上未经检验。该项目的目标是利用新建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（冰压力减去河床上的水压力）之间的关系。该装置将一圈融化的冰（外径 0.9 m，宽 0.2 m，厚 0.15 m）拖过硬或软的冰床。该装置的特点包括无限滑移位移、温度控制在百分之几度、以及连续观察床层的冰滑动和水流分离。一组实验将测试这一理论：随着滑移速度的增加，粗糙、坚硬的床上的稳定阻力达到最大值，然后保持恒定或减小，具体取决于床的几何形状。冰在其熔化温度下在阶梯状和正弦床表面上滑动期间，基础阻力、滑动速度和有效压力将单独变化。实验几何约束下的冰流数值模拟将使理论结果与实验数据直接进行比较。第二组实验将提供软层滑移速度、阻力和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层孔隙空间的程度，以及软层变形以适应滑动问题的程度——这对于评估冰川沉积物输送至关重要。需要稳健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，即以异常高的速度前进，并以不同的速度后退，显然是为了应对气候变化。该项目的实验研究将以实地观测无法确定的方式研究冰川运动。 对滑动过程进行更完整的分析将使冰川和冰盖运动的计算机模型能够更准确、更不随意地处理冰川滑动。这将有助于更好地描述不久的将来的环境变化和遥远的过去的景观演变。