Using Spatial and Temporal Variations of Ice Deformation to Study Basal Processes

主要研究人员将通过详细监测地表速度和内部冰变形来研究基底剪应力和基底运动的分布。假设基底应力的分布与内部变形场有关，基底条件的时间变化不仅表现为地表运动的变化，而且表现为内部变形的变化。考虑到冰的非线性流变和基础过程对有效压力变化的敏感性，这种内部变形的变化可能相对较大。主要研究人员将利用这些想法在阿拉斯加黑急流冰川上研究基底运动的机制。他们之前已经记录了冰下土壤层的存在，并对其性质有一些了解。观测和模拟研究表明，水压波动会引起这种冰的强度变化，而基础条件的这些时空变化又会导致冰变形场的可测量变化。六个钻孔将沿着斜井所在的横截面钻，第七个钻孔将在冰川下方钻。它们将配备倾斜传感器，用于连续监测钻孔变形，并配备压力传感器，用于监测基础水压。他们还将测量横断面上的地表速度及其时间波动。观测研究将在每年春季加速事件之前开始，并在夏季进行，此时各种运动事件发生。然后，伐木将在冬季条件更稳定的情况下继续进行。然后，将使用冰变形的有限元模型，根据基底剪切应力的分布和整个年周期中基底运动的潜在机制来解释这些数据。拟议的项目将充分利用与现有资助项目的协同合作，在与我们的中心钻孔相同的位置，在底部底部深层安装倾斜传感器。总而言之，主要研究人员将能够更全面地了解基础过程以及基础运动和冰变形之间的相互依存关系。在冰流和冰川对气候变化的反应的简单模式中，这种相互依存关系通常被忽略。

Abstract EchelmeyerOPP-01-15819 The Principal Investigators will study the distribution of basal shear stress and basal motion through detailed monitoring of surface velocities and internal ice deformation. The hypothesis is that the distribution of basal stress is related to the internal deformation field, and that temporal changes in basal conditions manifest themselves not only as changes in surface motion, but as changes in internal deformation. Such changes in internal deformation can be relatively large given the non-linear rheology of ice and the sensitivity of basal processes to variations in effective pressure. The Principal Investigators will investigate the mechanisms of basal motion using these ideas on Black Rapids Glacier, Alaska. They have previously documented the presence of a subglacial till layer and have some knowledge of its properties. Observational and modeling studies have shown that water pressure fluctuations cause changes in the strength of this till, and that these spatial and temporal changes in basal conditions then lead to measurable changes in the ice deformation field. Six boreholes will be drilled along a cross section where the till exists, and a seventh will be drilled further downglacier. They will be instrumented with tilt sensors for continuous monitoring of borehole deformation and with pressure transducers for monitoring basal water pressure. They will also measure surface velocities across the transects, and their temporal fluctuations. The observational study will be initiated before the annual spring speed-up event and carried through the summer, when various motion events occur. Logging will then continue through the more steady conditions of the winter season. A finite element model of ice deformation will then be used to interpret these data in terms of the distribution of basal shear stress and the underlying mechanisms of basal motion throughout the annual cycle. The proposed project will take full advantage of synergetic collaboration with an existing, funded program to install tilt sensors deep in the underlying basal till at the same location as our central borehole. Taken together, the Principal Investigators will be able to obtain a more complete picture of basal processes and of the interdependence of basal motion and ice deformation. Such interdependence is usually neglected in simple models of ice flow and the response of glaciers to climate variations.