Abstract

During the 1989 melt season, ten tracer experiments were conducted to investigate seasonal, diurnal, and spatial variations in the internal drainage system in the ablation area of Storglaciären, Sweden. Dye was injected into moulins, and dye concentration and discharge were monitored in two streams at the glacier terminus, Sydjåkk and Nordjåkk Dye emerged only in Sydjåkk

Transit velocities ranged from 0.07 to 0.29 m/s, implying that drainage was through a well-defined conduit system. Velocity and discharge relations suggest that these conduits are part of a multi-branched arborescent network of individually braided, wide, low passages. A progressive decline in dispersivity during the early part of the melt season reflects structural changes in these conduits, presumably including a decrease in the degree of braiding and an increase in size. The system reached its late-season configuration in early August, by which time the energy dissipated by the flowing water would have sufficed to melt between 0.7 and 21 m3 of ice per meter of conduit length, depending on conduit size. Potential closure rates exceed melt rates on conduit walls throughout most of the drainage system, and so conduits are probably full of water during periods of higher daily discharge, with water pressures exceeding atmospheric pressure. Variations in tracer-return curves and dispersivity on a diurnal time scale also appear to reflect changes in the degree of braiding, in this case resulting from drowning of low divides between channels as discharge increases.

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