Date of Award

Spring 1-1-2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geological Sciences

First Advisor

Robert S. Anderson

Second Advisor

Gerard Roe

Third Advisor

Peter Molnar

Fourth Advisor

Gregory Tucker

Fifth Advisor

Harihar Rajaram

Abstract

Glaciers change length in response to fluctuations in climate. In addition, atmospheric and geomorphic processes modulate glacier response to climate change. These factors must be explored in detail to understand glacier response. I engage two factors modulating glacier response: 1) the effect of year-to-year weather variability on glacier length and 2) the effect of debris cover on glacier dynamics. I use case studies from the Last Glacial Maximum (LGM) in Colorado in addition to modern glaciers in the Nepalese Himalaya and Alaska to address these issues.

The effect of interannual variability on the moraine record

Multi-decadal, kilometer-scale fluctuations in glacier length occur in response to stochastic, year-to-year variability in mass balance. I address the effect of weather variability on our interpretation of the moraine record using glacier models in the Colorado Front Range during the LGM. My analyses suggest that (1) glacial standstills longer than 50 years were unlikely; (2) mean glacier lengths are ~10%-15% up-valley from maximum glacier lengths; and (3) individual LGM terminal moraines were formed by a combination of a climate change and interannual variability-forced advances.

Numerical modeling of debris-covered glaciers

Debris cover can significantly affect the length and dynamics of valley glaciers. I developed a 2D vertical plane long-valley numerical glacier model with which we explore the feedbacks between debris and ice dynamics. Debris input to the glacier in the accumulation zone emerges in the ablation zone, and is then advected along the glacier surface, damping melt rate. Debris cover reduces ice surface slopes, ice thickness gradients, ice discharge gradients, and englacial velocities in the ablation zone.

Ice cliffs on debris-covered glaciers

Debris cover suppresses ice melt on glaciers. However, the retreat of debris-free ice cliffs within otherwise debris-covered glaciers counters the insulating effects of debris. I provide a theoretical framework for the production and removal of ice cliffs and glacier surface topography on the Kennicott Glacier, Wrangell Mountains, Alaska. Mean debris thickness exerts primary control on glacier surface relief and ice cliff concentration. Approximately 30% of net mass loss from the study area is due to the retreat of ice cliffs.

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