Mechanics of Folding in Glaciers: A Numerical Study

冰川的折叠破坏了地层分层，改变了冰和其中夹带的任何沉积物的流动轨迹。褶皱的尺度从厘米到数百米不等，在冰川边缘附近特别明显，那里含有沉积物的冰带受到纵向压缩。虽然在这方面的褶皱的描述是丰富的，一个完整的理解，产生它们的机械条件是缺乏的。 一个普遍的假设是，当冰川通过均匀的应力场时，冰层会被动地变形。然而，冰-沉积物混合物与干净的冰相比具有显著不同的机械特性，这表明应力应该远非均匀。由此产生的不均匀的应变，因此沉积物的传输路径，可以由含沉积物的冰和周围的干净的冰之间的流变学差异。该项目将利用已建立的富含沉积物的冰和干净冰的流变学公式，评估机械上不均匀的冰分层对冰川褶皱运动学的影响。将使用商业有限差分代码（FLAC，伊塔斯卡咨询集团）模拟冰川环境中相关大应变的变形。主要结果将对照现有的分析和数值解进行检验。该项目将为解释含有沉积层的冰川褶皱提供一个有物理基础的框架。 褶皱层保存了冰穿过冰川时所经历的应力的复合记录。 应力的变化通常是由于冰川与河床耦合的时间或空间变化。 更好地了解分层的、含沉积物的冰如何对施加的压力作出反应，将有助于更有信心地解释引起褶皱的冰川学环境。这些结果也将拓宽预测冰原中的地层分层如何沿着沿着而受到干扰的基础，从而使冰芯中的地层定年任务复杂化。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，将冰川过程和结构地质学整合在一起，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.