Triggers of Rapid Change in Glacier Dynamics
Authors: Liu Jukes 
Published: January 2025

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.