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Canals under sediment-based ice sheets

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Abstract:

Classical theories of channelized subglacial drainage identify a melting vs creep balance at the channel–ice boundary that is crucial in determining its steady flow properties, but this consideration neglects the role of erodible–deformable basal sediments, especially in controlling channel morphology. Here we present a mathematical model for channels underneath ice sheets, which incorporates the detailed mechanics of sediment transport over a mobile till–bed interface, and which allows a variable, wide channel cross section also. The resulting drainage conditions depend on the sediment flux (q) as well as the water flux (Q) through the channel—these quantities being controlled by the rates at which sediment and meltwater are captured by the flow. An approximate analytical solution indicates a "canal"-type drainage law (Walder and Fowler, 1994) of the form Ncn ∝ Ψ−1 Q−5/2q3/2, where Nc is the effective channel pressure, n is the exponent in Glen's flow law for ice, and Ψ is the imposed hydraulic gradient (due to topography). By solving the downstream problem numerically, the canal characteristic has been confirmed and found to be insensitive to upstream conditions. Thus, low effective pressures can result from high basal water flux or melt rates. This supports the contention that canals may be a central component in fast ice flow over soft beds. The proposed model also establishes a fundamental link between the plumbing system of a glacier and its sediment budget.

Document Type: Research Article

DOI: http://dx.doi.org/10.3189/172756400781820633

Publication date: January 1, 2000

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  • The Annals of Glaciology is a peer-reviewed, thematic journal published 2 to 4 times a year by the International Glaciological Society (IGS). Publication frequency is determined and volume/issue numbers assigned by the IGS Council on a year-to-year basis and with a lead time of 3 to 4 years. The Annals of Glaciology is included in the ISI Science Citation Index from volume 50, number 50 onwards.

    Themes can be on any aspect of the study of snow and ice. Individual members can make a suggestion for a theme for an Annals issue to the Secretary General, who will forward it to the IGS Publications Committee. The IGS Publication Committee will make a recommendation for an individual themed Annals issue, together with a potential Annals Chief Editor for that issue, to IGS Council. The IGS Council will make the decision whether to proceed, taking into account the spread of topics and the overall capacity for publication of pages in Annals.

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