Cryo-geohazards in a warming climate: geophysical, hydrological, and remotely sensed investigations of glacial lakes, outburst floods, and rock glaciers
Rick, Brianna, author
McGrath, Daniel, advisor
Rathburn, Sara, committee member
McCoy, Scott, committee member
Klein, Julia, committee member
Changes to the cryosphere impact both societal and ecological communities, and understanding where changes have occurred in the past allow us to predict changes in the future, and help in creating plans to minimize or alleviate potential societal stressors. The overarching goal of this dissertation is to explore changes to the cryosphere at varying spatial and temporal scales, utilizing a range of methods from in situ measurements to large-scale remote sensing, exploring seasonal to annual to decadal scale changes. I investigate ice-marginal lake changes in Alaska (Chapter 2), document ice-dammed lake drainages in Alaska (Chapter 3), and explore the hydrological influence of the Lake Agnes rock glacier in Colorado (Chapter 4). Ice-marginal lakes impact glacier mass balance, water resources, and ecosystem dynamics, and can produce catastrophic glacial lake outburst floods (GLOFs). Multitemporal inventories of ice-marginal lakes are a critical first step in understanding the drivers of historic change, predicting future lake evolution, and assessing GLOF hazards. In Chapter 2, I use Landsat satellite imagery and supervised classification to semi-automatically delineate lake outlines for four, ~5 year time periods between 1984 and 2019 in Alaska and northwest Canada. Overall, ice-marginal lakes in the region have grown in total number (+183 lakes, 38% increase) and area (+483 km2, 59% increase) between the time periods of 1984–1988 and 2016–2019, though 56% of inventoried lakes did not experience detectable change. Changes in lake numbers and area were notably unsteady and nonuniform. I demonstrate that lake area changes are connected to dam type (moraine, bedrock, ice, or supraglacial) and the spatial relationship to their source glacier (proglacial, detached, unconnected, ice, or supraglacial), with important differences in lake behavior between the sub-groups. In strong contrast to all other dam types, ice-dammed lakes decreased in number (–6, 9% decrease) and area (–51 km2, 40% decrease), while moraine-dammed lakes increased (+56, 26% and +479 km2, 87% for number and area, respectively) at a faster rate than the average when considering all dam types together. Proglacial lakes experienced the largest area changes and rate of change out of any lake position throughout the period of study, and moraine-dammed lakes experienced the largest increases. Moraine-dammed lakes with large growth are also associated with clean-ice glaciers (<19% debris cover). By tracking individual lakes through time and categorizing lakes by dam type, subregion, and location, I detect trends that would otherwise be obscured if these characteristics were not considered. Chapter 2 highlights the importance of including lake characteristics when performing ice-marginal lake inventories, and provides insight into the physical processes driving recent ice-marginal lake evolution. Chapter 3 focuses specifically on ice-dammed lakes, as the glacial lake outburst flood record is dominated by these types of lakes, yet as I found in Chapter 2, ice-dammed lakes are decreasing in number and area. Rapid lake drainage (on the order of hours to days) can produce devastating outburst floods leading many to propose that hazards from glacial lakes are increasing. Outburst flood compilations do show an increase in number of events over time, however, recent studies attribute such trends to observational bias. This leaves large uncertainty about current and future glacial-lake hazards. Using multitemporal satellite imagery, I documented 1150 drainages from 106 lakes between 1985–2020, with an apparent increase in event frequency from 5 in 1985 to 70 in 2020. However, accounting for the increasing number of satellite images throughout the record, I find no temporal trend in drainage frequency. Furthermore, I document a loss of >75% of ice-dammed lakes since the 1960s. This suggests a decrease in regional flood hazard and motivates an unbiased look at other regions. As the world deglaciates, rock glaciers are important headwater features that have a delayed response to warming. Over 10,000 rock glaciers have been mapped in the contiguous United States, and 38% of these rock glaciers are found in Colorado. North American rock glaciers are estimated to have the third largest water volume equivalent by region, though these features are an often-disregarded component of the water budget in alpine basins. In this study, I incorporate geophysical, hydrochemical, and remotely sensed data to investigate the ice presence, movement, and hydrologic influence of the Lake Agnes rock glacier in the northern Front Range, Colorado. I observe an average horizontal velocity of 17 ± 5 cm yr-1 between 2019 and 2021 for the active lobe. Rock glacier streams remained below 2.5 °C throughout the summer, mixed-source streams remained below 3.5 °C, and the non-rock glacier stream reached 13.5 °C. The geophysical surveys suggest an internal rock glacier structure of an active layer ~3 m thick, underlain by an ice-poor layer up to 10 m thick, underlain by an ice-rich layer up to 18 m thick, with total rock glacier thickness between 20–30 m. This study confirms the presence of ice within the Lake Agnes rock glacier and documents its influence on basin hydrochemistry, elevating ion concentrations, pH, and maintaining low stream temperatures. In basins such as the Lake Agnes basin, the reduced climate sensitivity of rock glaciers and their sustained cold-water input to mountain streams will likely provide a refuge for cold-water species in a warming climate.
Includes bibliographical references.