From the moment a snowflake touches down on the surface of a glacier, it begins a process of transformation. Fresh snow, made up of single-grained snowflakes is compacted into glacial ice by the weight of subsequent snowfall and by sintering, grain boundary sliding and diffusion. At first, snow grains accommodate the stress through mechanical failure and by changing their shapes and positions. Fragile, dendritic structures on the edges of snowflakes break off, and grains round into lower free energy configurations. Rounded grains slip into air pockets. As time passes, increasing overburden of a load to bear, and it is, for a single snowflake. But it is precisely this stress that creates a glacier. Stress, in this case, is a catalyst for transformation. But don't worry. I am not going to make an overly forced metaphor for what happens during a doctorate program.} Pressure causes the grains to merge, large grains absorbing small ones. As ice grains squeeze and grow into all the available pore space, grains trap air bubbles and cut them off from the atmosphere, preserving records of climate conditions. Eventually, these processes densify the snow so thoroughly that it metamorphoses into glacial ice, and from a crumbly collection of snowflakes emerges a cohesive crystalline matrix. This process, firn densification, is the subject of my first chapter. From measurements of englacial strain rates by repeat phase-sensitive radar deployments, we show it is possible to extract densification rates that match modeled predictions.
The formation of ice is just the beginning of the story of a glacier. As and after ice forms, gravity pulls on the body of the glacier; ice flows under its own weight, becoming a viscous river that meanders from high elevations toward the sea level. Along the way, various other forces act on the ice (e.g., friction at the ice-bed causes ice to shear, narrowing valley walls create compressive stresses, etc.). This history can be written into the ice in the orientation and configuration of its molecular structure.
Ice is made of a regular crystal matrix of water molecules. Covalently bonded oxygen and hydrogen molecules assemble into sheets of hexagons, held to each other by hydrogen bonds. The relative orientation of these hexagonal sheets is called the "ice fabric”, and its importance lies in the fact that ice’s asymmetric molecular structure gives rise to asymmetric properties. For example, ice is softer—more deformable—when stress is applied parallel to the hexagonal planes, like playing cards sliding over one another. Over hundreds or thousands of years, this asymmetric response to stress causes the hexagonal planes to rotate so that they lie perpendicular to the direction of compressive stress. This, in turn, changes which relative direction a glacier is the “softest”. In short, the history of the glacier is written into its fabric. Ice remembers the stress it has undergone, and that memory changes its resistance to (or accommodation of) stress in the present and future.
In chapter two, I use an autonomous phase-sensitive radar to measure the ice fabric along a central transect of Thwaites Glacier. Thwaites drains ice from West Antarctica and is one of the fastest changing glaciers on the continent. Locked up in Thwaites is at least half a meter of sea level rise, as well as much of the buttressing that holds back WAIS. Measurements of the fabric of Thwaites tell us about the history of stress undergone by the glacier, as well as any change in relative direction of the "softest" ice.
As a glaciologist, I have dedicated my life to studying how glaciers form, flow, and disappear. As an artist and writer, I am interested in material memory, with a particular orientation toward ice itself and in the way the language and mathematics used to describe ice mimic processes that happen in body, mind, and society. My fourth chapter is centered on the creative research and art produced during my dissertation, particularly focused on a visual autoethnography of my body I created during my first field season in Antarctica in 2022-2023. In it, I try to grapple with whether/how, even as positivist science demands I remove as much of myself as possible from my scientific research, my body/myself show up in small ways in my data. I consider how ice's response to stress—to soften or harden, to flow or crack—is in many ways, a mirror for how we as humans respond to stress.
Other work in Chapter 4 was created in direct response to the beauty of glaciated landscapes and the grief I struggle to manage in response to their rapid change. Biome I is a short zine that uses faux-color satellite imagery overlain with text and meshes of glaciers from Grand Teton National Park (GRTE). In 2021, I spent six months as a Scientists-in-Parks fellow through AmeriCorps, joining the park's physical science team in Wyoming to expand their glacier monitoring program. From this work emerged Chapter 3 a history of glacial change in the park over the last 70 years from in situ and remotely sensed observations. This work, while quite different from my previous scientific output, allowed me to learn and explore other glaciological techniques as well as template methodologies and provide information that is immediately useful for education and action in GRTE and other rapidly deglaciating landscapes.
Much of the way I have come to understand glacial geophysics is by considering the ways they connect more broadly to our lived experiences. In the Tetons, this involved understanding how deglaciation affects the park's ecological systems and the evolving safety for visitors given the changing ice conditions. In pursuit of both expanding my own understanding and hoping to share with others the joy and beauty of the study of ice, I have developed numerous education efforts to make the study of glaciers, climate, and the earth physical, tangible, less abstract, emotional, joyful, and intuitive. Chapter 5 concludes the thesis by taking a step back to look at education and teaching, the thread that has carried through my doctorate, from prior to starting graduate school and, I hope, that will continue long after. I discuss the influences of teacher-philosophers like Shannon Mattern, Lynda Barry, and bell hooks, who have all, in their own way, striven to reshape the (idea of the) classroom into forms that better serve the learner. This work has taken place on the seat of a bicycle riding across the country, on an icefield in Juneau, Alaska, and in my own backyard, in classrooms across New York City.
To conclude, I hope this thesis is not only a scientific effort, but one that draws the curtain back on the broader work we do as glaciologists. We are also artists and educators, caretakers, archivists, and public figures. Our work can be physically, mentally, and emotionally demanding, and it is as often full of grief as it is of awe.
| Identifer | oai:union.ndltd.org:columbia.edu/oai:academiccommons.columbia.edu:10.7916/f47n-sx37 |
| Date | January 2024 |
| Creators | Case, Elizabeth |
| Source Sets | Columbia University |
| Language | English |
| Detected Language | English |
| Type | Theses |
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