2010 GSA Denver Annual Meeting (31 October 3 November 2010)
Paper No. 119-6
Presentation Time: 8:00 AM-6:00 PM


HUBBARD, Trent D., Alaska Division of Geological & Geophysical Surveys, 3354 College Road, Fairbanks, AK 99709, trent.hubbard@alaska.gov and REGER, Richard D., Reger's Geologic Consulting, P.O. Box 3326, Soldotna, AK 99669

Physiographic and stratigraphic evidence indicates that huge floods emanated from the Tok River valley in the upper Tanana River drainage during the last major (Donnelly) glaciation. Our investigations support an earlier suggestion by Schmoll (1984) that the ultimate source of those flood waters was Glacial Lake Atna in the northeastern Copper River basin. Water from Glacial Lake Atna inundated the lower Slana River valley and entered the upper Tok River drainage through Mentasta Pass.

Vesicular volcanic clasts from the Wrangell Mountains are key components of flood gravels. Their presence in morainal deposits in the lower Slana River Valley, coupled with key physiographic features, provide evidence that ice from the Wrangell Mountains south of the northeastern Copper River basin blocked the Slana River drainage. Thick lacustrine sand containing scattered pebbles of both Wrangell Mountains and Alaska Range lithologies overlies till of Alaska Range origin in the Slana River drainage, documenting the existence of a meltwater lake dammed between Wrangell Mountains ice and a relatively small, local valley glacier in the upper Slana River- Mentasta Pass-Mineral Lake area. We suggest that rising waters of Glacial Lake Atna eventually destabilized the massive Slana glacier dam, subglacially releasing voluminous lake waters that overtopped the valley glacier at ~690 m elevation in the Mentasta Pass area, breached the Mineral Lake terminal moraine, and poured down the Tok River drainage. At peak flows, flood waters reached an elevation of ~730 m at the Mineral Lake moraine, destroying the northwestern half of the moraine. Depths of the flood flow through the 2.8-km-wide morainal breach could have been ~166 m

Vesicular volcanic clasts of Wrangell Mountains derivation have been traced 80 km northward through the Tok River drainage and 95 km westward down the Tanana River. Dilution by the influx of Alaska Range rock types decreased the abundance of vesicular volcanic clasts in flood gravels from ~54 percent where flood waters entered the Tok River drainage to ~10 percent at the toe of the Tok expansion fan.

2010 GSA Denver Annual Meeting (31 October 3 November 2010)
General Information for this Meeting
Session No. 119--Booth# 406
Timing of Pleistocene Glaciation in the North American Cordillera (Posters)
Colorado Convention Center: Hall D
8:00 AM-6:00 PM, Monday, 1 November 2010

Geological Society of America Abstracts with Programs, Vol. 42, No. 5, p. 310

© Copyright 2010 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.