Constraining calving dynamics of marine-terminating glaciers: Developing 4D data of Store Glacier, Greenland, from repeat UAV photography

• Main Author: Vautrey, Jonathan
• Format: Thesis
• Language: English
• Published: Apollo - University of Cambridge Repository 2018
• Subjects: Greenland; glacier
• Online Access: https://dx.doi.org/10.17863/cam.35441; https://www.repository.cam.ac.uk/handle/1810/288126

In the past few decades several of the Greenland Ice Sheet’s (GISs) marine-terminating outlet glaciers have shown patterns of swift retreat and thinning, but the mechanism of calving, which controls this loss, is still not fully constrained. This research uses UAV-borne remote sensing data to analyse the calving events of Store Glacier, west Greenland, in order to develop our knowledge of this important glaciological process. Repeat aerial photography of the terminus of Store Glacier were collected by the RESPONDER project. These images were taken and run through photogrammetry software in order to produce 3D point clouds, and ultimately orthomosaics and DEMs of the calving front at a 20 cm spatial resolution. By doing this for the multiple sorties carried out by the UAV, 4D data was created, permitting detailed analysis of crevassing and calving processes over a 5-day period at a sub-daily temporal scale. Maps of the crevasses across the glacier front for each survey were produced through Gaussian blurring of the DEMs, and show a clear progression of the fractures over time. However, there is no strong connection between the crevasse patterns and observed calving events throughout the study period at this aerial view. The orientation of crevasses across moving and fixed transects, 100 m and 150 m from the glacier front respectively, were also obtained. Additionally, the principal axes of strain within the ice across the caving front were calculated from surface velocity and strain rate components. These two datasets were compared and reveal the influence of both Mode I and Mode III fracturing in the formation of crevasses across Store Glacier’s snout, with mixed mode fracturing also being common in some regions. But, the basal topography of the bed and overdeepening below Store Glacier may also play a key factor in controlling these patterns and the types of crevasses observed on the glacier surface. Finally, measurements of the dimensions of crevasses across these transects, plus depth profiles longitudinally up the glacier, show that the monitoring of individual crevasses provides a more robust method of determining how crevasse propagation influences the occurrence of calving events compared to their mass-measurement. A diurnal cycle of crevasse deepening is revealed, while the debutressing of the glacier front following a calving event seemingly also helps other surface crevasses and rifts to propagate due to the spread of tensile stresses in the local area. However, basal crevasses are also likely to contribute to the calving at Store Glacier and attempts should be made to continually monitor their development at the same time as surface crevasses in order to improve our understanding of the crevasse-calving relationship.