Mechanics of Folding in Glaciers: A Numerical Study

冰川的折叠破坏了地层分层，改变了冰及其夹带的任何沉积物的流动轨迹。褶皱出现的尺度从厘米到数百米不等，在冰川边缘附近尤其明显，那里含有沉积物带的冰受到纵向压缩。虽然在这种情况下对褶皱的描述是丰富的，但对产生它们的机械条件的完整理解是缺乏的。一种常见的假设是，当冰川穿过均匀应力场时，冰层会被动地变形。然而，冰-沉积物混合物的力学性质与干净的冰明显不同，这表明应力应该远非均匀的。由此产生的不均匀应变，以及沉积物的输送路径，可以由含沉积物冰和周围干净冰之间的流变学差异决定。该项目将利用已建立的富含沉积物冰和清洁冰的流变公式，评估机械不均匀冰层对冰川褶皱运动学的影响。商用有限差分代码（FLAC， Itasca咨询集团）将用于模拟与冰川环境相关的大应变变形。关键结果将根据现有的解析和数值解进行测试。该项目将为解释含沉积层的冰川褶皱提供一个物理基础框架。折叠的冰层保存了冰穿过冰川时所受压力的综合记录。应力的变化通常是由于冰川与床的耦合在时间或空间上的变化。更好地了解层状、含沉积物的冰是如何对施加的压力作出反应的，将使我们对产生褶皱的冰川学环境有更自信的解释。这些结果还将扩大预测冰盖地层分层如何随着流动而受到干扰的基础，使冰芯层定年的任务复杂化。此外，该研究还有助于分析岩层中的褶皱，这些褶皱发生在无法观察到的较长时间跨度内。该项目将制作一个实践教学模块，将冰川过程和构造地质学整合在一起，并将在互联网上广泛提供。

Folding in glaciers disrupts stratigraphic layering and changes flow trajectories of ice and any sediment entrained therein. Folds appear at scales ranging from centimeters to hundreds of meters, and are particularly evident near glacier margins where ice containing sediment bands undergoes longitudinal compression. While descriptions of folds in this context are plentiful, a complete understanding of the mechanical conditions that produce them is lacking. A common assumption is that layers become distorted passively as the glacier passes through homogeneous stress fields. However, ice-sediment mixtures have significantly different mechanical properties than clean ice, suggesting that stresses should be far from homogeneous. Resulting inhomogeneous strains, and therefore sediment transport paths, can be dictated by the rheological differences between sediment-bearing ice and surrounding clean ice. This project will evaluate the impact of mechanically inhomogeneous ice layering on fold kinematics in glaciers using established rheological formulations for sediment-rich ice and clean ice. A commercial finite difference code (FLAC, Itasca Consulting Group) will be used to simulate deformation to large strains relevant in glacial environments. Key results will tested against available analytical and numerical solutions.This project will provide a physically-grounded framework for interpretation of folds in glaciers containing sediment layers. Folded layers preserve a composite record of the stresses experienced by the ice as it passes through the glacier. Changes in stresses are often due to temporal or spatial changes in the glacier's coupling to the bed. A better understanding of how layered, sediment-bearing ice responds to imposed stresses will allow more confident interpretation of the glaciological circumstances that gives rise to folds. The results will also broaden the basis for prediction of how stratigraphic layering in ice sheets can be disturbed along flow, complicating the task of dating layers in ice cores. Furthermore, the study can contribute to the analysis of folding in rock formations, which occur over longer time spans that cannot be observed, This project will produce a hands-on teaching module integrating glacial processes and structural geology that will be made widely available on the internet.