T91 Reconstructing Environmental Controls on Societal Change from Prehistory to Present Day I

Monday, 26 September 2016
8:00 AM - 12:00 PM
Room 301

LINKS BETWEEN GEOMORPHIC PROCESSES, CLIMATE, AND HUMAN SETTLEMENT IN THE ISLANDS OF THE FOUR MOUNTAINS, ALASKA

Paper number: T91-13
Program: Technical Sessions
Time: 10:55 AM – 11:10 AM

Authors

Abstract

The Islands of the Four Mountains (IFM), gateway to the Central Aleutians, are remote and difficult to access. Consequently, little fieldwork has focused on geomorphic processes and their relationship to island morphology, climate change, and human settlement. We investigated glacial and fluvial processes on Carlisle and Tana volcanoes. The largest remaining glacier in the IFM is located in the east Tana valley. The eastern aspect is anomalous; many glaciers in the Aleutians occupy north-facing aspects. The valley is deeply eroded producing an unusually large basin, likely due to a pre-LGM sector collapse, and subsequent erosion in highly erodible hydrothermally altered rock. Similarly, Little Ice Age moraine morphology in the east Tana Valley is influenced by hydrothermal alteration. Moraines on the south side of the valley are sharp crested and composed of dacitic and andesitic clasts. Moraines of the same age on the northern side of the valley are composed of fine grained clays in highly altered volcanic rock. The finer material results in greater rates of creep and more rounded moraine crests than moraines on the south side of the valley. Neoglacial moraines indicate that Neoglacial Period glaciers were significantly larger. As ice receded, the east Tana valley was prone to paraglacial debris flows enhanced by the weak rock. No evidence of human settlement was observed in the east Tana valley despite a perennial water source and suitable village sites above the likely elevation of tsunamis. On the Carlisle volcano, a village site is situated adjacent to an ephemeral stream on a large dissected alluvial fan featuring a distributary drainage network. Sedimentation at the fan head may have diverted flow away from the channel near the village and into the current perennial channel, initiating incision there. At the base of the fan are thick (20 m) debris flow deposits, which do not contain evidence of human settlement. Archeological sites, dating to ~ 4.0 ka, are restricted to the upper ~ 3 m of the fan stratigraphy. The Late Pleistocene deglacial landscape would have been prone to debris flows and. This unstable landscape may have resulted in conditions unfavorable to human occupation. These observations suggest a link between geomorphic process and village sites in the IFM requiring further investigation.

Geological Society of America Abstracts with Programs. Vol. 48, No. 7

doi: 10.1130/abs/2016AM-287937

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