Microstructures in a shear margin: Jarvis Glacier, Alaska

Article Abstract 

Microstructures, including crystallographic fabric, within the margin of streaming ice can exert strong control on flow dynamics. To characterize a natural setting, we retrieved three cores, two of which reached bed, from the flank of Jarvis Glacier, eastern Alaska Range, Alaska. The core sites lie ~1 km downstream of the source, with abundant water present in the extracted cores and at the base of the glacier. All cores exhibit dipping layers, a combination of debris bands and bubble-free domains. Grain sizes coarsen on average approaching the lateral margin. Crystallographic orientations are more clustered and with c-axes closer to horizontal nearer the lateral margin. The measured fabric is sufficiently weak to induce little mechanical anisotropy, but the data suggest that despite the challenging conditions of warm ice, abundant water and a short flow distance, many aspects of the microstructure, including measurable crystallographic fabric, evolved in systematic ways.

What we know: The way in which glaciers flow depends on the properties of the tiny grains of snow and ice that the glacier is made of.  

Why it’s important: Glaciers might move either faster or slower than predicted, depending on the temperature, shape and orientation of these grains.  This is extremely important if we hope to predict how glaciers and ice sheets are likely to change as the climate warms.

How the research was done:  Scientists collected a series of three ice cores from a glacier in Alaska to study the properties of snow and ice grains.  They specifically chose an area of complicated glacier flow in order to understand how snow and ice grains deform under different conditions.

What the evidence shows: The authors found consistent patterns in the microscopic properties of ice that may help us understand how glacier flow will change under future conditions.