Item: Unsteady heat flow from a buried melt-freeze crust
Title: Unsteady heat flow from a buried melt-freeze crust
Proceedings: Proceedings of the 1982 International Snow Science Workshop, Bozeman, Montana, USA
Authors: Richard Armstrong, Rocky Mountain Forest and Range Experiment Station, Alpine Snow and Avalanche Project, 240 West Prospect St., Ft. Collins, Colorado 80526
Abstract: When a melt-freeze crust which remains at or near O°C is buried by a colder snow layer a condition of unsteady heat flow develops. How long would this transient temperature condition continue before a return to the steady heat flow along the persistent gradient between the ground heat source and the cold air above? What possible effect on local metamorphism might be expected? The first question is treated in this presentation while the second is left for speculation and discussion among the workshop participants. Starting with a uniform temperature distribution within the buried crust, the surface is suddenly altered to and maintained at a colder temperature corresponding to the new snow layer. A series of step-wise calculations are used to determine successive temperature distributions through specified increments of time until the gradient becomes steady or linear. For example, preliminary calculations indicate that a 5.0 cm thick, 700 kg m-3 density melt-freeze crust buried by a layer of new snow at -lOoC would return to a linear gradient in approximately one-half hour, while a 100 em, 500 kg m-3 rain-soaked layer would require approximately 6 days. Thermal diffusivity, defined by the ratio of thermal conductivity to heat capacity, is used to calculate the propagation of temperature waves into or out of a layer. Diffusivity is far less density dependent than its component terms since they both increase with increasing density.
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Keywords: diffusivity, melt-freeze crust, metamorphism
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