lecture_6 - LECTURE 6 THERAMAL AND FLOW PROPERTIES OF...

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LECTURE 6 – THERAMAL AND FLOW PROPERTIES OF GLACIERS THERMAL PROPERTIES Warm glaciers are at the pressure melting point Peculation and refreezing of meltwater elevates the internal temperature of ice to the pressure melting point (LHF=80cal/g). The melting point of ice is lowered 0.0072 0 ° C per atmosphere of pressure (ice skate affect) Under 1,500m of ice at the pressure melting point the melting temperature of ice is -1 ° C. The surface of a glacier is chilled seasonally (< 5 m) when winter air temperatures are reduced to below 0 ° C. The temperature gradients from the bed to the surface of warm glaciers are positive. CONCLUSION: Heat from internal friction associated with ice flow as well as basal sliding will melt about 0.01-0.02 m/year of ice from the bed of the glacier. Heat from the geothermal heat flux (~38cal/cm 2 /yr) will melt about 0.005 to 0.01 m/year of ice A film of water will thus occur at the bed of a warm glacier, even in winter when there is no surface melting. Most warm glacier occur in temperate areas where there is heavy snowfall and intense summer melting. Cold glaciers are below the pressure melting point throughout.
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Persistent cold air temperatures at the ice surface chill the ice to considerable depths (>100 m). Under these conditions temperature gradients from the bed of the ice to the surface are generally negative. Temperature gradients can be affected by changes in climate or advection of colder ice from upstream. CONCLUSION: Heat generated from internal friction, basal sliding, or from the geothermal heat flux will be conducted to the glacier surface Thin cold glaciers will tend to be frozen to their beds whereas thick cold glaciers can have water present at their beds - f(surface temperature, ice thickness). Most cold glaciers occur in alpine or polar areas where there is light snowfall and little melting. ICE FLOW CHARACTERISTICS GENERAL OBSERVATIONS Glaciers flow because the imbalance between accumulation and ablation leads to an increase in the surface slope of a glacier, which increases its shear stress until it deforms or flows. The movement of glacier ice is generally laminar and normally < 1m/day. Ice movement in a valley glacier generally leads to a parabolic form - generally more rapid at the center where it is thickest and least along the margins. Ice movement in a “U” shaped valley generally leads to a U shaped form, whereas movement in an asymmetric valley leads to a distorted parabolic form. An ice stream bounded by marginal shear zones can
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lead to plug or block flow.
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