Graduate Thesis Or Dissertation
Glacier Detachments and Landslide Hazards in a Changing Climate Public Deposited
The rapid warming of the cryosphere is having a profound effect on natural hazards in glaciated regions. As glaciers retreat and permafrost thaws, new glacial lakes and unstable valley walls are forcing communities to adapt to the evolving hazards. A vivid reminder of the dangers these changes can pose came in 2016, when two low-angle glaciers in Tibet detached from their beds and avalanched down the valley, killing nine people. Of the 28 similar events in the historical record, 17 have occurred since the year 2000 -- suggesting that glacier detachments may be a newly emerging hazard. In this dissertation, I seek to understand what causes glacier detachments and whether we can infer past events from the resulting deposits.
I begin by investigating the 2013 and 2015 detachments of Flat Creek Glacier in Alaska's St. Elias Mountains (Chapter 2). I conclude that these detachments were triggered by an unusually high input of meltwater to a glacier system prone to instability due to a weak glacier bed and a glacier tongue partially frozen to the ground. These are the same conditions that are believed to have led to the detachments in Tibet. In revealing this striking similarity, I provide the basis for determining which glaciers may be at risk of detaching. Furthermore, the demonstrated importance of liquid water as a trigger suggests that glacier detachments will increase in frequency as temperatures rise.
To determine whether glacier detachments are indeed becoming more frequent, we need to know how often they occurred in the past. With a followup study at Flat Creek (Chapter 3), I provide the first detailed description of a detachment deposit and assess whether it can be distinguished from other types of glacio-fluvial deposits. I find that the detachments left behind unique features, including streamlined furrows, vast fields of densely-packed hummocks, and shallow thermokarst depressions. The deposits also lack a coarse-grained carapace or grain size sorting, further differentiating them from those formed by rock avalanches and debris flows. Based on these findings, glacier detachments can now be taken into account when interpreting the geologic record, both for the reconstruction of (paleo)environments and for reliable hazard assessments.
Glacier detachments have demonstrated how incomplete our understanding of cryospheric hazards can be, and highlighted the need for better monitoring tools. In Chapter 4, I evaluate the power of interferometric coherence -- a data-quality metric produced as part of interferometric radar processing -- for assessing the pre-failure activity of slope instabilities. Using the example of the Mud Creek landslide in California, I show that a loss of coherence on the landslide, relative to the surrounding hillslope, can indicate instability months before the failure.
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