Date of Award

5-2019

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Earth Sciences

Advisor

Christopher Gerbi

Second Committee Member

Peter Koons

Third Committee Member

Seth Campbell

Abstract

The lateral margins of glaciers and ice streams play a significant role in glacial flow. Depending on their properties, like temperature and ice crystal orientation, they can cause a resistance to flow or enhance it. In combination with our current changing climate, flow patterns can dictate the mass balance of an ice body. It is therefore more important than ever to understand the impact that variations at the margins can have on flow. However, the lateral margins of glaciers and ice streams are an often-neglected part of ice dynamics; they are harder to sample than the center of a glacier’s flow path because of debris and crevassing, so we have little data about them. We are attempting to change that. To assess the sensitivity of flow to material properties of the ice, I join computer modeling with measurements taken on the lateral margin of a mountain glacier. My sensitivity analysis is two-fold: 1) I combine synthetic geometries and parameters to provide conclusions regarding the effect lateral margins have on glacier flow, and 2) I use properties of Jarvis Glacier, Alaska as a case study for the input of in situ fabrics and temperatures into my model.

In complementary work, we have measured the geometry and velocity of Jarvis Glacier, Alaska, as well as the thermal profile and crystal orientation at two locations 25 m and 100 m from the lateral margin. This access to a realistic scenario provides a reference for the sensitivity tests, allowing us to understand what parameters have the greatest impact on 3D glacial velocity. In the following chapters, the questions I address in depth are: 1) to what extent do ice crystal fabric and temperature in the lateral margins matter in determining glacial flow, and 2) have we accurately captured the essential mechanics of these parameters and their relationship to flow? Results show that while Jarvis’s warm lateral margin temperatures do alter flow, the glacier’s weakly-oriented fabric does not. However, if the ice crystals in a glacier were more oriented than they are in Jarvis, flow could double, or even triple, especially if the glacier has a frozen bed. By adding just 10 m of highly oriented ice crystals to the sides of an ice body, flow increases by 26% and that number rises the farther into the glacier I assign the oriented fabric. Temperature changes create similar patterns. My models produce expected stress and strain rate relationships throughout the ice body and can capture part of the deformation occurring naturally in Jarvis; horizontal shear in my model matches what we measured in Jarvis near the surface and underestimates what we measured in Jarvis near the bed. This deviation near the bed is most likely from weak till or water, variables that my model does not account for. To address these missing components in the future, a user could manipulate the open-source modeling software I am using as a platform for this project. Given the potential influence of parameters like crystal orientation and temperature on the overall movement of an ice body, it is imperative we both acquire more data at the lateral margins of glaciers and ice streams as well as include those data into flow calculations to more accurately model and predict the behavior of ice.

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