PhD defence: Mads Dømgaard

Mads Dømgaard defends his thesis, 

Remote Sensing of the Cryosphere - Expanding Observations on Glacier Dynamics and Related Glacial Phenomena

Supervisor:
Assistant professor Anders Anker Bjørk, IGN

Assessment Committee:
Professor James Lea, University of Liverpool
Associate Professor Bert Wouters, Technical University Delft
Associate professor Stéphanie Horion (chair), IGN

Abstract:

Over the past decades, the cryosphere has undergone massive changes, including accelerating mass loss from glaciers and ice sheets, primarily driven by climate changes caused by anthropogenic greenhouse gas emissions. Extended time series are invaluable for detecting, understanding, and predicting future changes in the cryosphere. However, in many regions, observational time series are still relatively limited. As a result, this thesis aims to expand our knowledge of glacier dynamics and glacial phenomena in Greenland and Antarctica by extending existing observational records through the exploration of historical aerial image archives and modern remote sensing data.

Specifically, Papers I, II, and III utilize historical aerial images to reconstruct past glacier changes and study glacier dynamics in Greenland and Antarctica, whereas Papers IV and V investigate glacial lake outburst floods (GLOFs) in Greenland using modern near-field and satellite remote sensing techniques.

Paper I presents the earliest glacier reconstructions in Antarctica, revealing 85 years of stability and growth in Lützow-Holm Bay, Kemp and Mac Robertson Land, and Ingrid Christensen Coast in East Antarctica. These long-term changes in surface elevation align with trends in snowfall during the same period. Paper II reconstructs the collapse of the Wordie Ice Shelf, Antarctic Peninsula, since 1966, attributing the disintegration primarily to increased basal melt from warming ocean temperatures. The tributary glaciers showed a substantial dynamic response, with a tripling of ice velocities and grounding line retreats of up to 13 km. However, the timing of the glacier response varied due to differences in the loss of ice shelf buttressing. Paper III documents how the collapse of Midgaard Glacier, East Greenland, starting in the 1930s, triggered multiple flow reconfigurations and ice flow piracy, ultimately leading to recent observed changes.

Paper IV analyzes one of the most comprehensive and longest records of GLOFs in Greenland, revealing significant annual fluctuations in drainage volume and timing, varied drainage mechanisms, and a recent rerouting of drainage water in 2021. Lastly, Paper V provides the first Greenland-wide mapping of GLOFs, showing a 1200% increase in the number of draining lakes compared to previous estimates and substantial fluctuations in the annual number of events.

Collectively, the PhD thesis highlights how expanding observational records enhances our knowledge of ongoing processes and mechanisms, and emphasizes the importance of understanding long-term changes when assessing current dynamics. Moreover, extended records are vital for projection future changes, whether in detecting early signs of ice shelf collapses and related glacier responses or in predicting potential hazards from GLOFs.

A digital version of the PhD thesis can be obtained from the PhD secretary at phd@ign.ku.dk before the defence. After the defence the thesis will become available from the Royal Danish Library Royal Danish Library | kb.dk