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Using Deformation Measurements to Constrain Ice Motion on a Land-terminating Region of the Greenland Ice Sheet
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| 자료유형 | 학위논문 |
|---|---|
| 서명/저자사항 | Using Deformation Measurements to Constrain Ice Motion on a Land-terminating Region of the Greenland Ice Sheet. |
| 개인저자 | Maier, Nathan T. |
| 단체저자명 | University of Wyoming. Geology & Geophysics. |
| 발행사항 | [S.l.]: University of Wyoming., 2019. |
| 발행사항 | Ann Arbor: ProQuest Dissertations & Theses, 2019. |
| 형태사항 | 182 p. |
| 기본자료 저록 | Dissertations Abstracts International 81-04B. Dissertation Abstract International |
| ISBN | 9781687932952 |
| 학위논문주기 | Thesis (Ph.D.)--University of Wyoming, 2019. |
| 일반주기 |
Source: Dissertations Abstracts International, Volume: 81-04, Section: B.
Advisor: Humphrey, Neil F. |
| 이용제한사항 | This item must not be sold to any third party vendors.This item must not be added to any third party search indexes. |
| 요약 | Ice flow along the margins of Greenland Ice Sheet (GrIS) is fundamentally under constrained. In this dissertation we use a dense array of inclinometers installed in a borehole network and GPS surface velocities to constrain ice motion during winter, the melt season, and across multi-year time scales at a field site in Greenland. Using the entire network of 212 inclinometers, we partition out the winter surface motion into its deformation and sliding components. We find that 96% of the surface motion is due to sliding, far higher than is expected outside of the melt season on a slow-moving and land-terminating region underlain by a hard bed. Further, using a novel modelling approach, we constrain the basal boundary to consist of sparsely-spaced bedrock asperities 10s of meters in scale which provide the limited resistance to sliding. Finally, we use margin wide estimates of the driving stress and flow speeds to show that sliding-dominated motion is typical of marginal ice flow and surface motion can be considered mainly sliding.During the melt season we continuously estimate the basal shear stress using the integrated force balance method and compare the variations to surface velocities and measurements of englacial shearing made near the bed. We find the bed rapidly strengthens and weakens during the melt season and is frequently in extreme states with basal tractions of more than three times the background values and close to zero. The extreme stress states occur during critical stages of melt season flow: during the spring speed, at the transition between the inferred switch from inefficient to efficient drainage, and as velocities decline during the late melt season. The continuous modulation of stress is found to be from local and non-local forcings indicating the integrated spatiotemporal effect of distributed meltwater forcings must be considered to fully understand melt season velocities. Finally, we show the stress changes observed cannot be accommodated by traditional sliding laws, suggesting debris-bed friction may be important to melt season flow and sliding relations. Over a multi-year period we look at the spatial structure of sliding and deformation across the borehole grid and investigate how it changes. We show surface velocity patterns expressed at the surface do not reflect, and are almost opposite of, the sliding patterns observed at the bed. Using ice flow models, we show the borehole grid straddles a slippery-sticky basal sliding transition zone which produces the sliding, deformation, and surface patterns observed. This basic pattern persists through the melt season and through the multi-year period showing the slippery-sticky transition zone is a stable feature of the basal architecture. Finally, we show that inter-winter changes in flow speeds are primarily a result of changes in the properties of the slippery region induced during late melt season flow. |
| 일반주제명 | Geology. Climate change. Environmental science. |
| 언어 | 영어 |
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