Earth’s glaciers, ice sheets, and ice shelves are changing significantly due to our warming climate. Glaciers that drain the Antarctic Ice Sheet have become more susceptible to rapid speed-up and retreat, especially once their floating portions become unstable or collapse. The world’s mountain glaciers are experiencing substantial melting and changing dynamics. Yet, the cryosphere is riddled with unsolved instabilities, unexplored tipping points, and unresolved ice-dynamic mysteries. This dissertation presents three studies that address three key topics in glaciology: drivers of ice shelf/fast-ice collapse, causes of rapid tidewater glacier retreat, and controls on mountain glacier waves called ‘ogives.’

First, in Chapter 2, I analyze and discuss the causes of the break-up of the decade-old Larsen B fast-ice that occurred in mid-January 2022. My study uses a plethora of satellite remote-sensing datasets, including optical imagery (primarily Landsat, MODIS, Sentinel-2, Worldview), synthetic aperture radar data (Sentinel-1), passive microwave data (AMSR-E/2), laser altimetry data (ICESat-2), aerial photography, and Worldview-derived digital elevation models (DEMs). I include ERA-5 and WaveWatch-III climate and ocean reanalysis data, and ice velocity measurements from in-situ GNSS data. By synthesizing all of these datasets, I diagnose the drivers of the fast-ice collapse and the initial glacier responses. Although 2022 was an anomalously warm year, the primary cause of the collapse was a large oceanic swell that broke up the fast-ice, the timing of which was associated with a corridor of low sea ice concentration in the northwestern Weddell Sea. Following the fast-ice break-out, the tributary glaciers and their ice tongues that earlier flowed into the embayment responded immediately. Crane, Hektoria, and Green Glacier lost their 300+ meter-thick floating ice tongues over the course of several weeks and then began calving at their grounding lines. Within a year, Crane Glacier accelerated by 50% and retreated 11 km.

In Chapter 3, I investigate Hektoria Glacier’s unprecedented rapid retreat and extended dynamical response to the break-out. For this analysis, I include ASTER and SPOT-5 HRS stereo-image-derived DEMs, ICEBridge radar data, and POLENET seismological data. I find that Hektoria and Green Glaciers accelerated by 600%, increased their thinning rate by 30-fold and Hektoria Glacier ultimately retreated by 25 km, 10 km of which was over a lightly grounded “ice plain” (an area of bedrock with a very low slope). I propose that the geometry of the ice plain preconditioned the thinning glacier for a rapid buoyancy-driven retreat. Until now, this process has not been recorded in the modern day glaciological record.

In Chapter 4, I investigate a set of ogives formed on the Gilkey Glacier, Alaska. Ogives are topographic wave trains that can form where an icefall connects to a valley glacier below. I employ a combination of remote sensing and in-situ observations, such as the ITS_LIVE velocity dataset, GNSS station data, Worldview imagery and DEMs, and Landsat imagery, to characteristize ice plateau-icefall-glacier systems. Those constrain parameter values in a finite difference numerical model that simulates ogive formation by calculating ice thickness changes resulting from varying mass balance and/or ice velocity. I use this model to test two main ogive formation processes using both an idealized glacier and the Gilkey Glacier. My results suggest that the most plausible explanation for ogive formation is a steady icefall velocity encountering a receiving glacier with significant seasonal velocity variation. During the summer, the lower glacier accelerates, inducing thinning at the base of the icefall. As the glacier decelerates in winter, it induces thickening at the base of the icefall, thus resulting in annual waves (aka ‘ogives’). Taken together, all three studies in this dissertation emphasize the importance of curiosity-driven science and the innate pursuit of knowledge.