Solving the mystery of surging glaciers

Solving the mystery of surging glaciers

Top image: The calving glacier Aavatsmarkbreen in Forlandsundet. Photo: Heïdi Sevestre/UNIS

PhD candidate Heïdi Sevestre has investigated the global distribution of surge-type glaciers and uncovered differences in geometry between normal and surge-type glaciers. Her research has helped solve one of the biggest enigmas in glaciology. Sevestre will defend her PhD thesis at UNIS on 13 October 2015.

12 October 2015
Press release from the University Centre in Svalbard (UNIS) and the University of Oslo.

Surge-type glaciers regularly undergo long periods of slow flow, and short period of extremely rapid flow, the surge. Surge-type glaciers represent only 1 to 2% of the glaciers in the world, however in Svalbard up to 20% of the glaciers are of this type. Even though surge-type glaciers are so few, their behaviour has remained one of the biggest enigmas in glaciology.

Heïdi Sevestre has investigated the global distribution of surge-type glaciers and uncovered differences in geometry between normal and surge-type glaciers. Results showed that surge-type glaciers found in specific climatic conditions and are larger, flatter and branchier than normal glaciers. Such patterns are interpreted in terms of a new conceptual framework, the enthalpy cycle model, in which surges are understood as natural oscillations in response to the way glaciers interact with their environment.

Mapping six Svalbard glaciers
The surge mechanisms of Svalbard glaciers were also tested by mapping the thermal structure of a sample of six glaciers of different sizes and dynamics. These were Von Postbreen, Tunabreen, Kongsvegen,  Midtre Lovenbreen, Longyearbreen and Tellbreen.

Presently cold and thin glaciers underwent a thermal cycle during the LIA maximum, yielding a corresponding switch in behaviour. Large surge-type glaciers remain warm-based during quiescence, demonstrating that thermal switch is not the trigger to surging. The behaviour of both small and large glaciers can be explained in the framework of the enthalpy cycle model.

Nathorstbreen, Spitsbergen, Svalbard. Photo: Eva Therese Jenssen/UNIS.

Heïdi Sevestre did a detailed study of the surge of Nathorstbreen in Van Keulenfjorden. Photo: Eva Therese Jenssen/UNIS

Finally, the chronology of two surges in Svalbard was investigated in details. The surge of Nathorstbreen in Van Keulenfjorden emitted seismic events detected 100 km further north in Longyearbyen, but only during the first 3 months of the surge. Localization of the events revealed that the rupture of one of the tributaries of Nathorstbreen is the source of this short-lived seismicity. Pre-surge transfers of mass were detected by DEM differencing. The advance of the glacier coincided with the failure of the frozen terminus.

The upward propagating surge (surge starting in the frontal part of the glacier) of calving glacier Aavtsmarkbreen in Forlandsundet is the result of a combination of increase in driving stress due to terminus steepening, and routing of surface meltwater through large extensional crevasses.

Dissertation
Heïdi Sevestre will defend her thesis for the PhD degree, entitled “Surge-type glaciers: controls, processes, distribution”, on 13 October 2015 at 12:30 in auditorium “Lassegrotta” at UNIS.

She will hold a trial lecture entitled “Ice sheets, glaciers and sea-level rise” at 10:15 the same day at UNIS.

Heïdi Sevestre. Photo: Gregory Rohart.

Heïdi Sevestre. Photo: Gregory Rohart

About the candidate:
Heïdi Sevestre was born in 1988 in Annecy, Haute-Savoie, France. She studied physical geography at the University of Lyon 3 (France).

In 2010, she completed her master’s degree in Glaciology at the Department of Geography & Earth Sciences at Aberystwyth University, Wales, UK.

In 2011 she started her PhD studies at UNIS and the University of Oslo, in the field of glacier surges.

Contact information: heidi.sevestre@yahoo.fr