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Mechanics of Deformable Glacier Beds

Citation

Minchew, Brent Morton (2016) Mechanics of Deformable Glacier Beds. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9MS3QN2. http://resolver.caltech.edu/CaltechTHESIS:12112015-113320636

Abstract

My focus in this thesis is to contribute to a more thorough understanding of the mechanics of ice and deformable glacier beds. Glaciers flow under their own weight through a combination of deformation within the ice column and basal slip, which involves both sliding along and deformation within the bed. Deformable beds, which are made up of unfrozen sediment, are prevalent in nature and are often the primary contributors to ice flow wherever they are found. Their granular nature imbues them with unique mechanical properties that depend on the granular structure and hydrological properties of the bed. Despite their importance for understanding glacier flow and the response of glaciers to changing climate, the mechanics of deformable glacier beds are not well understood.

Our general approach to understanding the mechanics of bed deformation and their effect on glacier flow is to acquire synoptic observations of ice surface velocities and their changes over time and to use those observations to infer the mechanical properties of the bed. We focus on areas where changes in ice flow over time are due to known environmental forcings and where the processes of interest are largely isolated from other effects. To make this approach viable, we further develop observational methods that involve the use of mapping radar systems. Chapters 2 and 5 focus largely on the development of these methods and analysis of results from ice caps in central Iceland and an ice stream in West Antarctica. In Chapter 3, we use these observations to constrain numerical ice flow models in order to study the mechanics of the bed and the ice itself. We show that the bed in an Iceland ice cap deforms plastically and we derive an original mechanistic model of ice flow over plastically deforming beds that incorporates changes in bed strength caused by meltwater flux from the surface. Expanding on this work in Chapter 4, we develop a more detailed mechanistic model for till-covered beds that helps explain the mechanisms that cause some glaciers to surge quasi-periodically. In Antarctica, we observe and analyze the mechanisms that allow ocean tidal variations to modulate ice stream flow tens of kilometers inland. We find that the ice stream margins are significantly weakened immediately upstream of the area where ice begins to float and that this weakening likely allows changes in stress over the floating ice to propagate through the ice column.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Earth Science, Geophysics, Glaciology, Geodesy, Remote Sensing
Degree Grantor:California Institute of Technology
Division:Geological and Planetary Sciences
Major Option:Geophysics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Simons, Mark
Thesis Committee:
  • Tsai, Victor C. (chair)
  • Thompson, Andrew F.
  • Lamb, Michael P.
  • Ampuero, Jean-Paul
  • Simons, Mark
Defense Date:28 October 2015
Non-Caltech Author Email:minchewb (AT) gmail.com
Funders:
Funding AgencyGrant Number
NASA Cryospheric SciencesNNX14AH80G
NASA Earth and Space Science FellowshipUNSPECIFIED
ARCS Foundation FellowshipUNSPECIFIED
ARCS and Albert Parvin Foundation FellowshipUNSPECIFIED
Record Number:CaltechTHESIS:12112015-113320636
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:12112015-113320636
DOI:10.7907/Z9MS3QN2
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.3189/2015JoG14J023DOIArticle adapted for ch. 2
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:9319
Collection:CaltechTHESIS
Deposited By: Brent Minchew
Deposited On:22 Dec 2015 18:09
Last Modified:18 May 2017 18:44

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[img] Video (MPEG) (Movie, vertical position, Rutford Ice Stream) - Supplemental Material
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[img] Video (MPEG) (Movie, horizontal flow, Rutford Ice Stream) - Supplemental Material
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