Abstract

In June 1987, Carroll Glacier (Glacier Bay, southeast Alaska) began to surge southeastward toward Wachusett Inlet. Between 9 June and 1 July 1987, the terminus advanced with a mean velocity of 29 m/day, slowing afterward but attaining a net displacement of >1 km by July 1988. A proglacial lake lay directly in the path of the surge and became partly overridden, with only 25% of its former basin remaining exposed after 1 yr.

The effects of the ice advance on the lake were profound. Early in the surge, lake-water samples attained suspended-sediment concentrations exceeding 9 g/L well above bottom. Extremely rapid sedimentation, locally attaining 8 m in 36 days, produced nearly uniform water depths of 8-9.5 m by August 1987. Sediment deposited during the surge was extremely soft and underconsolidated, composed of massive to irregularly layered muddy silt produced by disruptions of the lake floor and by remobilization of lake-bottom sediment by sediment gravity flows. A prominent push moraine, developed from a low ridge initiated by glacial loading, formed where the glacier overrode sandy substrate, but no similar feature was observed in the muddy lake floor.

By July 1988, the surge had greatly diminished, and the remaining lake basin was slowly uplifted by displacement from the weight of the ice. By the end of August 1988, most of the lake floor was completely exposed and undergoing erosion by meltwater channels, causing abnormally high suspended-sediment loads at the outlet compared to the previous year when the lake was an effective sediment sink.

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