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Abstract

Malaspina Lake is a large proglacial lake which lies along the southeastern margin of the Malaspina Glacier, Alaska. It is density stratified with respect to suspended sediment content, which ranges from 0.1 grams per liter at the surface to 0.7 grams per liter at a depth of 45 m. The lake is not thermally stratified since water near the temperature of its maximum density (3.94°C) occurs close to the lake surface and water as cold as 0.3°C occurs at the lake bottom.

Two large surface streams, Russell Stream and Tarr Stream, flow into the lake, and their combined discharge was measured at 140 cubic meters per second. Discharge from the lake ranged from 490 cubic meters per second to 600 cubic meters per second, and thus subglacial and englacial streams were apparently discharging as much as 460 cubic meters per second into the lake. Tarr Stream, which loses suspended sediment in a series of small lakes that act as settling basins, enters the lake as an overflow. Russell Stream and Tunnel Stream, which is an englacial stream, are both highly charged with suspended sediment and enter the lake as continuous turbidity currents or underflows. Two underflows and two interflows were recorded along the ice-contact margin of the lake. These underflows and interflows apparently originate from englacial or subglacial streams discharging into Malaspina Lake.

Bottom topography of the lake is quite irregular except where the selective infilling of basins by turbidity currents has produced flat to gently sloping topography. Cores taken from these flat areas contain varved sediments. Varves, deposited at depths of SO m or more, contain numerous normal and reverse graded beds. The current-bedded portion of the varve was deposited from an underflow or turbidity current. The varve was completed by the deposition of a clay unit from suspension when continuous underflows, or turbidity currents, ceased during the winter months.

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