Thermally controlled glacier surging

Abstract

Bakaninbreen in Svalbard and Trapridge Glacier in Yukon Territory, Canada, are two prominent examples of surging glaciers which are thought to be controlled by their thermal regime. Both glaciers have developed large bulges which have propagated forward as travelling wave fronts, and which are thought to divide relatively stagnant downstream cold-based ice from faster-moving warm-based upstream ice. Additionally, both glaciers are underlain by a wet, metres thick layer of deforming till. We develop a simple model for the cyclic surging behaviour of these glaciers, which interrelates the motion of the ice and till through a description of the subglacial hydrology. We find that oscillations (surges) can occur if the subglacial hydrological transmissivity is sufficiently low and the till layer is sufficiently thin, and we suggest that these oscillations are associated with the development and propagation of a travelling wave front down the glacier. We therefore interpret the travelling wave fronts on both Trapridge Glacier and Bakaninbreen as manifestations of surges. In addition, we find that the violence of the surge in the model is associated with the resistance to ice flow offered by undulations in the bed, and the efficiency with which occasional hydrological events can release water accumulated at the glacier sole.

Surge dynamics in the Nathorstbreen glacier system, Svalbard

“…Areas gaining the largest amount of mass during quiescence will reach enhanced gravitational forcing prior to surrounding areas. In stage 1 this results in locally increased velocity in areas with temperate bed conditions followed by a relative increase in frictional heat at the bed, thus generating more subglacial melt water (Fowler et al, 2001). We assume that englacial water storage is similar to that during quiescence.…”

“…Differences in observed surge characteristics and dynamics have also led to a suggestion of at least two separate surge mechanisms between polythermal and temperate glaciers (Murray et al, 2003a). Surges in polythermal glaciers were explained by changes in basal thermal regime that are controlled by a thermal mechanism (Murray et al, 2000;Fowler et al, 2001), while the temperate surges were explained by a hydraulic mechanism (Kamb, 1987). Detailed spatial measurements of surge onset are rare due to the difficulty in predicting them.…”

A surge of the glaciers Skobreen–Paulabreen, Svalbard, observed by time-lapse photographs and remote sensing data

“…As noted above, Bakaninbreen surged from 1985 to 1995, but the surge terminated before reaching the front and caused no advance. In a series of papers (Porter et al 1997;Murray et al 1998;Murray et al 2000;Fowler et al 2001;Murray & Porter 2001), it was shown that downglacier propagation of the surge front was associated with thawing of the glacier bed, and that flow acceleration reflected enhanced basal motion over a thin layer of unfrozen basal till.…”

“…When a glacier surges, ice velocities can increase by one or two orders of magnitude, drawing down ice from reservoir areas towards the front, in some cases producing ice-front advances of several kilometres. These radical transformations reflect switches in the thermal and/or hydrological conditions at the glacier bed, resulting from some combination of internal dynamic processes and external environmental conditions (e.g., Kamb et al 1985;Eisen et al 2001;Fowler et al 2001;Hewitt 2007). The classic definition of surging glaciers emphasizes quasi-periodic velocity fluctuations, in which glaciers cycle between periods of rapid motion lasting a few months to several years*the surge or active stage*and periods of slow flow lasting several years to decades*quiescent periods (Meier & Post 1969;Dowdeswell et al 1995).…”

A note on the water budget of temperate glaciers

“…caused by frictional heating related to strongly enhanced sliding (Budd, 1975;Kamb et al, 1985;Sharp, 1988;Fowler et al, 2001;Van Pelt and Oerlemans, 2012). It is unclear how large the supply of water from this dissipation process is in relation to the supply of melt water and rain.…”