Publication Date
5-2024
Date of Final Oral Examination (Defense)
2-28-2024
Type of Culminating Activity
Dissertation
Degree Title
Doctor of Philosophy in Geophysics
Department Filter
Geosciences
Department
Geosciences
Supervisory Committee Chair
Ellyn M. Enderlin, Ph.D.
Supervisory Committee Member
T. Dylan Mikesell, Ph.D.
Supervisory Committee Member
H. P. Marshall, Ph.D.
Supervisory Committee Member
Christine Dow, Ph.D.
Abstract
The loss of land ice has become the greatest contributor to global mean sea level rise since 2006 (Oppenheimer et al., 2019). Glaciers have contributed ∼20% to global sea level rise over the last ∼2 decades (Oppenheimer et al., 2019; Hugonnet et al., 2021), while the ice sheets have contributed 33% (Oppenheimer et al., 2019). For the outlet glaciers and ice streams that drain the Greenland and Antarctic ice sheets, changes to their dynamics (flow speed, thickness, and length) dominate their present and future mass loss (King et al., 2020; Diener et al., 2021). One of the main limitations in predicting future glacier mass loss under future emissions scenarios is the lack of representation of glacier instabilities in global models. Global glacier models still do not adequately represent the processes that govern the development of instabilities from perturbations at the ice-rock and ice-ocean interfaces (glacier bed and terminus, respectively) due to knowledge gaps that arise, in part, from the difficulty of directly observing these interfaces.
For my dissertation, I developed automated methods for processing large remote sensing datasets to observe changes in glacier dynamics at fine spatial and temporal scales. I focused methods application on the two regions outside the ice sheet with the highest rates of mass loss – Greenland’s periphery and Alaska – rather than the ice sheets because the dynamics of glaciers outside the ice sheets are governed by the same controls and because these regions are relatively under-studied but important to global glacier mass loss. In Chapter 2, I applied a novel edge detection algorithm developed throughout my Master of Science thesis to satellite images to automatically trace glacier terminus positions in the Landsat image record. With this method, I analyzed change in length for the glaciers along the Greenland periphery at sub-seasonal timescales with much greater efficiency than possible with manual traces. After applying this method to the hundreds of marine-terminating glaciers around Greenland’s periphery, I discovered a synchronous, anomalous retreat in 2016 amongst 56 glaciers in southeast Greenland. I analyzed their length change time series with respect to environmental datasets to evaluate whether anomalous retreat was triggered primarily by perturbations at the glacier terminus or bed. In Chapters 3 and 4, I developed new satellite image feature-tracking pipelines for generating additional glacier velocity maps in order to better capture glacier surges (cyclical, order-of-magnitude speedups triggered by instabilities at the glacier bed). I focused primarily on Sít’ Kusá, a surging glacier in southeast Alaska, but demonstrated the utility of the pipeline for four other surge-type glaciers in the Northern hemisphere (Chapter 3). In Chapter 4, I analyzed the feature-tracking velocities alongside glacier surface elevation and temperature time series to explore dynamics at seasonal to multi-year cycles throughout an entire surge cycle of Sít’ Kusá.
Analysis of the automated glacier change observations for southeast Greenland and Alaska revealed complexity in the interplay of external (environmental) and internal factors that influence glacier dynamics at sub-seasonal to multi-year timescales. The studies presented in this dissertation were the first to show that (1) the mountain glaciers in Greenland can undergo anomalous, synchronous retreat in response to an annual surface melt anomaly and that (2) surging glaciers can undergo annual order-of-magnitude speedups outside of their surges, challenging the traditional definition of the quiescent phase. The annual speedups were linked to seasonal evolution of the glacier hydrological system and were primarily driven by surface meltwater input modulated by summer air temperatures. My findings indicate that the combination of glacier geometry and surface meltwater feedbacks can trigger speedup and retreat instabilities. These processes should be incorporated into models in order to accurately predict how glaciers will change as air temperatures continue to rise. Other novel dynamic behavior may be resolved with the efficient, high temporal-resolution analyses provided by the automated pipelines for producing observations of glacier retreat/advance and speedup presented throughout the dissertation. They are open-source, provided publicly as tools for the glaciological community for future adaptation and use.
DOI
https://doi.org/10.18122/td.2179.boisestate
Recommended Citation
Liu, Jukes, "Triggers of Rapid Change in Glacier Dynamics" (2024). Boise State University Theses and Dissertations. 2179.
https://doi.org/10.18122/td.2179.boisestate
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