Dynamical unity of "Alaskan-type" and "Svalbard-type" glacier surges
Abstract
It is commonly stated that glacier surges are of two distinct types: Alaskan-type (relatively short cycles, 1-2 year surge phases, high peak velocities) and Svalbard-type (multi-decadal to centennial cycles, multi-year surge phases, lower peak velocities). These differences are sometimes attributed to the distinct mechanisms of hydrologic and thermal switching, respectively. Our observations and modelling, however, indicate that all surges are manifestations of the same underlying principle: that glaciers can only maintain stable steady states if their mass and enthalpy (internal energy) budgets simultaneously balance. Particular combinations of climate, glacier geometry, and bed properties are antagonistic to balanced mass and enthalpy budgets, leading to oscillatory behaviour. Enthalpy balance theory makes the important prediction that "Svalbard-type" and Alaskan-type" surges occur by essentially the same mechanism:an excess of enthalpy gains over losses, and consequent build-up of water at the bed.
We present mass and enthalpy budget analyses for surges in Svalbard (Morsnevbreen) and Alaska (Variegated Glacier), and compare results with model runs for corresponding climatic conditions. For most of its 140-year cycle period, Morsnevbreen had very low mass flux and an enthalpy budget characterized by slight excess of geothermal heating over conduction and/or water discharge. Transition to surge occurred over a 20-year period in response to the onset of sliding and frictional heating, followed by a velocity-friction feedback and a faster velocity-crevassing-water influx feedback. At Variegated Glacier, sliding persists throughout the ~15 year surge cycle, and the evolution of enthalpy sources during quiescence is closely similar to the transition phase of Morsnevbreen. Hydrologic switches are implicated in the termination of both surges, although they differ in detail. In both cases, the data are consistent with model predictions, and we conclude that the principal difference between the surges is simply the absence of long, low-enthalpy quiescent phase at Variegated Glacier. This difference reflects climatic influences on the glacier mass and enthalpy budgets, and not any fundamental contrast in surge mechanisms.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.C54A..02B
- Keywords:
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- 0726 Ice sheets;
- CRYOSPHERE;
- 0774 Dynamics;
- CRYOSPHERE;
- 0776 Glaciology;
- CRYOSPHERE;
- 0798 Modeling;
- CRYOSPHERE