A Step in Understanding Glacial Flow: Exploring the effects of entrained
insoluble debris on mechanical properties of polycrystalline ice
Abstract
An improved understanding of the mechanisms and factors affecting
glacial flow is crucial to better predict sea level rise. Glacial ice
often contains impurities such as the presence of small insoluble
particles. Mixtures of ice and dust can be found in many places
throughout the world, specifically in areas of high latitude and
altitude (Moore, 2014). This study aims to understand the effect of
entrained insoluble debris on processes of glacial motion. Glaciers move
through a combination of internal ice deformation and basal sliding.
Internal ice deformation, the flow of individual ice grains, has been
found to be grain-size dependent in both field and laboratory studies
(Goldsby and Kohlstedt, 2001). In an attempt to better understand ice
grain size, this study considers the effect of debris on grain growth.
Samples of pure ice and ice with debris were fabricated with a standard
protocol and maintained at -5°C for controlled annealing.
Microstructural characterization was preformed using a light microscope
to image the samples, and calculating the average grain sizes using a
linear-intercept method. The ice with debris was found to have smaller
grain sizes, thought to be associated with grain-boundary pinning.
Extrapolated values were used with a flow law, projecting that ice with
debris will have lower viscosity, thus flow faster. To address basal
sliding, the other form of glacial movement, we conducted a second phase
of study. Basal sliding, the process of a glacier sliding over the
bedrock, is influenced by the presence of meltwater at the base of the
glacier (Hoffman et al., 2011). Frictional heating, from ice-on-rock
friction, was studied as a factor affecting meltwater production. We
conducted a simple 1D computer model using laboratory friction
measurements of ice with entrained debris (Zoet et al., 2013). We find
that debris content and frictional heating are directly proportional.
Trials run at faster glacial velocities also show larger amounts of
frictional heating. As frictional heating may increase meltwater,
glaciers with debris may slide faster over bedrock. Overall, by better
understanding the motion of debris-rich glaciers, we can focus our
attention to areas around the world at risk, and better predict/prepare
for sea level rise.