The Cryosphere Discuss., 7, 5613-5657, 2013
www.the-cryosphere-discuss.net/7/5613/2013/
doi:10.5194/tcd-7-5613-2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper is under review for the journal The Cryosphere (TC).
Oscillatory subglacial drainage in the absence of surface melt
C. Schoof1, C. A. Rada1, N. J. Wilson2, G. E. Flowers2, and M. Haseloff1
1Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, Canada
2Department of Earth Sciences, Simon Fraser University, Burnaby, Canada

Abstract. The presence of strong diurnal cycling in basal water pressure records obtained during the melt season is well-established for many glaciers. The behaviour of the drainage system outside the melt season is less well understood. Here we present borehole observations from a surge-type valley glacier in the St Elias Mountains, Yukon Territory, Canada. These indicate the onset of strongly correlated multi-day oscillations in water pressure in multiple boreholes straddling a main drainage axis, starting several weeks after the disappearance of a dominant diurnal mode in August 2011 and persisting until at least January 2012, when multiple data loggers suffered power failure. Jökulhlaups provide a template for understanding spontaneous water pressure oscillations not driven by external supply variability. Using a subglacial drainage model, we show that water pressure oscillations can also be driven on a much smaller scale by the interaction between conduit growth and distributed water storage in smaller water pockets, basal crevasses and moulins, and that oscillations can be triggered when water supply drops below a critical value. We suggest this in combination with a steady background supply of water from groundwater or englacial drainage as a possible explanation for the observed wintertime pressure oscillations.

Citation: Schoof, C., Rada, C. A., Wilson, N. J., Flowers, G. E., and Haseloff, M.: Oscillatory subglacial drainage in the absence of surface melt, The Cryosphere Discuss., 7, 5613-5657, doi:10.5194/tcd-7-5613-2013, 2013.
 
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