Dynamical change at tidewater glaciers examined using time-lapse photogrammetry
Retreating glaciers and ice sheets provide a significant contribution to sea level rise, which will affect future populations and their activities. Accurate sea level projections are needed in order to best inform policy makers, but these projections are limited by our understanding of dynamical change at marine-terminating glaciers. Terrestrial time-lapse photography has proved to be a viable approach for obtaining high-detail observational records, and is used here to examine signals of dynamical change at two tidewater glaciers in Svalbard. Photogrammetric measurements were extracted using PyTrx (`Python Tracking'), a new photogrammetry toolbox that has been developed here for deriving velocities (e.g. glacier surface velocity), surface areas (e.g. supraglacial lake area, surfacing plume area), and line distances (e.g. terminus profiles). PyTrx has been created as a Python-alternative photogrammetry software, and offers additional functionality to the typical monoscopic feature-tracking toolboxes that are currently available. Subglacial hydrology and its relation to basal sliding were examined at Kronebreen, Svalbard. The results revealed a difference in flow efficiency between the north and south regions of the glacier tongue, which influences spatial patterns in surface velocities. Long-term changes in ice flow were concluded to be controlled by the location of effcient and inefficient drainage, and the position of regions where water is stored and released. Changes in terminus conditions and calving processes were examined at Tunabreen, a surge-type tidewater glacier. Observations suggested that atmospheric forcing plays a larger role in terminus stability than previously considered, and it is likely that terminus dynamics at Tunabreen are the product of a unique interplay between oceanic and atmospheric forcing which are shaped by the glacier's surge-type nature. Additionally, calving activity at Tunabreen can be characterised as high-frequency, low-magnitude events, and a high proportion of its long-term calving activity can be attributed to the rate of under-cutting at the terminus. In all, these studies demonstrate that long-term changes in glacier dynamics are dictated by the small changes in basal and terminus conditions, and how they vary from year-to-year. Future research now needs to be directed towards understanding how small-scale processes vary over multiple melt seasons, in order to establish how they operate at longer timescales. PyTrx provides an appropriate basis to continue this work and expand the capabilities of the toolbox.