Abstract

Thick sections of Wisconsin and younger deposits exposed in recently deglaciated Adams Inlet, Glacier Bay National Monument, southeastern Alaska, reveal the glacial history of the area. Following deposition of the late Wisconsin Granite Canyon till, Forest Creek glaciomarine sediments were laid down. These sediments contain volcanic ash that may have been derived from Mt. Edgecumbe 200 km south of Adams Inlet on Kruzof Island. Wood on top of the Forest Creek sediments is dated at 10,940 ± 155 yrs B.P. Land was nearly 90 m lower than present levels; it rose an average of at least 2 cm per year, causing retreat of the sea. Adams Inlet and tributary valleys were then filled in Hypsithermal time with glacial out-wash and inwash gravel. By 1700 B.P., the entrance to Adams Inlet had been dammed by growing fans forming glacial Lake Adams in the inlet and adjacent valleys. Glacier ice of Neoglacial time then advanced into the lake. Retreat of this ice from the tributary valleys to the central part of the inlet was followed by deposition of a local sandy outwash into the valleys. The time of this retreat and the stabilization of Adams Inlet Glacier possibly coincides with the Little Optimum (A.D. 1150 – 1300). Adams Inlet Glacier then expanded to its maximum Neoglacial extent about A.D. 1700, and it may have remained there as late as 1835. Several glacial lakes formed in tributary valleys during subsequent deglaciation. Deposits of these lakes, glaciofluvial deposits, and till comprise the Glacier Bay Formation in Adams Inlet. Retreat from Neoglacial position is well documented by historical observations.

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