Water and Sediment in the Norris Glacier Outwash Area, Upper Taku Inlet, Southeastern Alaska

ABSTRACT An 8-square mile outwash fan, composed of gravelly sediment, extends from the terminus of Norris Glacier to the waters of upper Taku Inlet, southeastern Alaska. Thirty-seven surface sediment samples and 11 cores from the tidal portion of the fan form the bulk of this study. The tidal flat is largely composed of very poorly sorted muddy sediment and relatively well sorted sand which, for the most part, overlie outwash gravel. Mixing of various modal size classes has produced a complex sediment distribution pattern as well as a complicated size-sorting relationship. The sand-size fraction of the sediments consists of feldspar, quartz, rock fragments, amphiboles, pyroxenes, micas, and opaques; the clay-size fraction consists of micas, chlorite, montmorillonite, feldspar, and amphibole. > The sediments are the product of glacial abrasion in the Juneau Ice Field area. The sand and mud are derived largely from Norris and Taku Glacier detritus; their nature indicates valley glacier detritus may be fairly rapidly sorted when subjected to hydraulic action. Absence of quartz and presence of feldspar in the claysize fraction may indicate that the physical properties of these minerals control the size to which they can be reduced by valley-glacier abrasion. Permeability and salinity measurements indicate that although the outwash is covered with saline water at high tide, water draining out of the outwash at low tide is essentially fresh. This shows that the sediment-water relationship is dynamic and glacial meltwater is now flowing through the outwash.