The Microstructural Heterogeneity of Ice in Jarvis Glacier, Alaska

Glacier ice behaves as a viscous fluid, where flow is controlled by a number of external and internal processes. One crucial, yet sometimes overlooked, factor is ice microstructure. Studies have shown that ice crystal (grain) size, shape, and orientation influence the viscous strength of ice, and therefore its resistance to flow and deformation. Glacier flow is also impacted by friction at the bed and lateral margins. The magnitude of flow resistance due to the lateral margins is not well quantified. The goal of this overall project is to evaluate how heterogeneous optical properties of ice are that are influenced by strain. Ice cores were drilled in a partial transect across Jarvis Glacier, a small, mountain glacier located in Eastern Alaska. Three ice cores were selected for making thin sections and analyzing under cross-polarized light. They were drilled at different distances from the lateral margin, and therefore should experience varying magnitudes of friction from the margin. Studies show that bubbles can potentially be used as strain markers in ice by examining their elongation and orientations. Using borehole televiewer imagery, larger dipping structures were categorized and their orientations and dip angles plotted. Image analyses of grain size, circularity, bubble shape and orientation indicate that these properties are heterogenous between ice cores. Heterogeneity among these measurements suggests that flow models may need to adjust to incorporate the intricate and important impacts that grain and subgrain processes have on ice dynamics such as flow magnitude