Year of Award

2018

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Geosciences

Department or School/College

Department of Geosciences

Committee Chair

Joel T. Harper

Commitee Members

Jesse V. Johnson, Marco Maneta, Toby W. Meierbachtol, Johnnie N. Moore

Keywords

Climate, Glacier mass balance, Glaciers, Greenland Ice Sheet, Ice dynamics, Radiostratigraphy

Publisher

University of Montana

Abstract

Glacier and ice sheet geometry depend on climatic and ice dynamic processes that are coupled and often highly complex. Thus, partitioning and understanding the drivers of change to glacier and ice sheet geometry requires creative approaches.

Radiostratigraphy data document emergent layers in the ablation zone of western Greenland that emulate theoretical englacial flow paths. Yet true alignment between radar layers and the englacial flow field can be uncertain because these structures have travelled hundreds of km from their original point of deposition, have been shaped by ice deformation for millennia, and have been subjected to complex and three-dimensional ice motion across steep and rugged bedrock terrain. In Chapter 2 I address this problem. Using ice dynamics information from a thermomechanically coupled, higher order ice sheet model, in conjunction with an observationally based test built on principles of mass conservation, I demonstrate that real world effects do not disrupt alignment between targeted ablation zone emergent radar layers and the local, present-day ice flow field.

Topographically driven processes such as wind-drifting, avalanching, and shading, can sustain mountain glaciers situated in settings that are otherwise unsuitable for maintaining glacier ice. Local topography can thus disrupt the way regional climate controls glacier retreat, which limits insight into the climate representativeness of some mountain glaciers. In Chapters 3 and 4 I address this issue. Analyzing glaciological, geodetic, and meteorological data, I quantitatively demonstrate that the glacier-climate relationship at a retreating cirque glacier evolved as mass balance processes associated with local topography became more influential from 1950 to 2014. I then assess regional glacier area changes in the Northern Rockies from the Little Ice Age glacial maxima to the modern. I characterize terrain parameters at each glacier and estimate glacier thickness. Using these data and extremely simple models of ice mass loss I assess climatic, topographic, and glaciological drivers. Predictable factors like initial glacier size, aspect, and elevation only partly explain the observed pattern of glacier disappearance. This implies that less predictable and poorly resolved processes like avalanching and wind-drifting drive spatially complex patterns of glacier mass change across this mountain landscape.

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© Copyright 2018 Caitlyn Elizabeth Florentine