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ABSTRACT Measurements of discharge, reach morphology, and cross-section morphology in supraglacial streams on the Juneau Icefield reveal controlling variables that have analogous counterparts in alluvial streams. Downward sky radiation imparts a strong diurnal pattern to supraglacial runoff generated by saturated slush flows, precipitation and melting, channel erossion, and spillover from water-filled moulins, crevasses, and supraglacial lakes. Supraglacial streams are generated when runoff is concentrated on glacier slopes and rates of incision exceed rates of glacier surface ablation. Streams leave the surface via moulins and crevasses where the water becomes part of the englacial and subglacial drainage systems. Meander systems develop and migrate downstream, driven by thermal erosion with heat supplied by climatic and hydrologic sources. Sinuosity attains a maximum value, in the absence of other roughness factors, when high stream power is imposed from an adjacent upstream reach. Form-process relationships for supraglacial meanders are similar to those for alluvial streams in spite of the contrast in time and scale of development. At-a-station hydraulic geometry for supraglacial streams serves to identify channel adjustments to changing discharge not unlike those for narrow-deep, straight alluvial streams. Daily formation of longitudinal grooves in channel walls leaves a record of daily flow and yields critical information regarding channel enlargement ratios. Fluvial adjustment toward equilibrium conditions involves all elements of channel roughness and cannot be analyzed using any single indicator such as channel pattern, cross-sectional shape, or materials involved.
Richard A. Marston (Thu,) studied this question.