Collaborative Research: Influence of natural ice microstructure on rheology in general shear: in-situ studies in the Alaska Range

了解冰川和冰原的冰的损失以及由此导致的海平面上升是至关重要的。格陵兰冰原和南极冰原以及高山冰川，主要通过冰的河流排放；因此，了解是什么控制着这些冰河中的水流类型，对于理解和预测海平面上升至关重要。在被认为是影响冰流的重要因素中，最不为人所知的因素之一是流动冰川两侧附近冰的内部强度。这种粘性强度反过来又可能受到冰川中冰晶的微观结构的影响。研究人员建议在阿拉斯加山脉东部的贾维斯冰川上详细研究这些关系，最终目标是能够在冰川流动的数值模型中表示微观结构的影响。为此，研究人员将首先使用地表速度测量、通过探地雷达获得的冰川几何知识以及数值模拟来确定钻探地点。然后，他们将通过横向和垂直流动梯度收集地面层的岩心。从钻孔中获得的速度和温度测量将补充地面测量，并使研究人员能够产生更复杂的三维数值模型，以测试研究区域内流动模式对机械结构的敏感性。他们将把冰芯的微观结构（如晶粒尺寸分布、晶体结构）与现场和模拟的速度和温度进行比较。虽然实验表明，晶体结构的强度和取向的变化可能导致流动强度的差异高达10倍，但很少有对流动冰的微观结构的原位观察研究；大多数对冰微观结构的研究都来自于冰缝，那里的流速是最慢的。在该项目结束时，研究人员的目标是确定(1)基于冰运动学的研究区域中织物形成的可预测程度，以及(2)通过数值模型计算的测量晶体取向织物强度，晶粒尺寸，温度和冰粘度之间的关系。织物和粘性强度之间的相关性表明，雷达和地震各向异性等遥感技术可能成为识别冰的流变结构的更有力的方法。另外，粘性强度和织物之间缺乏紧密联系表明，其他因素对流变特性起着重要的控制作用。因此，无论微观结构与粘性强度之间的相关性如何，拟议项目的结果都应该提高对流动冰的物理规律的定量理解，并改善未来冰质量平衡的预测。该项目将支持和参与研究生和本科生。该项目的数值模型将开发成一个公开的基于网络的图形用户界面，供其他研究人员和课堂使用。

Understanding the loss of ice from glaciers and ice sheets, and the resulting sea-level rise, is of critical importance. Both the Greenland and Antarctic Ice Sheets, as well as mountain glaciers, discharge primarily though rivers of ice; understanding what controls the type of flow that occurs in these rivers of ice is therefore central to understanding and predicting sea-level rise. Among the least-understood factors that are thought to be important in affecting ice flow is internal strength of the ice near the sides of a flowing glacier. This viscous strength, in turn, may be affected by the micro-scale structure of the ice crystals in the glacier. The investigators propose to examine these relationships in detail on Jarvis Glacier, in the eastern Alaska Range, with the ultimate goal of being able to represent the effects of microstructure in numerical models of glacial flow.To do this, the investigators will first use surface velocity measurements, knowledge of the glacier geometry derived from ground penetrating radar, and numerical modeling to identify a site for drilling. They will then collect surface-to-bed cores across lateral and vertical flow gradients. Velocity and temperature measurements derived from the boreholes will complement the surface measurements and allow the investigators to produce a more sophisticated three-dimensional numerical model to test the sensitivity of flow patterns to the mechanical structure within the study area. They will compare the microstructure (e.g., grain size distribution, crystallographic fabric) in the ice cores to the in-situ and modeled velocities and temperatures. Although experiments suggest that variations in the intensity and orientation of the crystallographic fabric can result in up to a ten-fold difference in flow strength, there are very few in-situ observational studies of the microstructural architecture of streaming ice; most studies of ice microstructure come from ice divides, where flow rates are slowest. At the end of this project, the investigators aim to have determined (1) the degree to which fabrics formed in the study area are predictable based on ice kinematics, and (2) the relationship among measured crystallographic orientation fabric intensity, grain size, temperature, and ice viscosity as calculated through numerical models. A correlation between fabric and viscous strength would suggest that remote sensing techniques such as radar and seismic anisotropy could become an even more powerful method for identifying the rheological structure of ice. Alternatively, the lack of a strong link between viscous strength and fabric indicates that other factors exert significant control on the rheological properties. Therefore, the results of the proposed project, whatever the correlation between microstructure and viscous strength, should improve quantitative understanding of the physical laws governing streaming ice and improve future predictions of ice mass balance. The project would support and involve both graduate and undergraduate students. The project's numerical models will be developed into a publicly available web-based graphical user interface for use by other researchers and in the classroom.