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Stilwell, K.B., 1995

Late Quaternary glacial geology, shoreline morphology, and tephrochronology of the Iliamna/Naknek/Brooks Lake area, southwestern Alaska

Bibliographic Reference

Stilwell, K.B., 1995, Late Quaternary glacial geology, shoreline morphology, and tephrochronology of the Iliamna/Naknek/Brooks Lake area, southwestern Alaska: Logan, Utah, Utah State University, M.S. thesis, 162 p.

Abstract

This study focuses on the late Wisconsin Brooks Lake glaciation, lake-level fluctuations, and volcanic deposits in the Iliamna/Naknek/Brooks Lake area on the northern Alaska Peninsula, southwestern Alaska. The Brooks Lake glaciation consists of five stades, from youngest to oldest: Kvichak, Iliamna, Newhalen, Iliuk, and Ukak. This thesis reassigns the type Mak Hill moraine to a pre - late Wisconsin glaciation, and considers the moraine enclosing Naknek Lake an early-late Wisconsin deposit correlative to either the Kvichak stade, Iliamna stade, or both. The presence in the Iliamna Lake valley, and the absence in the Naknek Lake valley of a twofold earliest-late Wisconsin Kvichak/Iliamna glacial sequence suggest that the two glacial systems responded differently to climate change, or glacier/bed dynamics due to differing ice sources and glacier configurations. Slope angles on the type Kvichak and Iliamna moraines are less steep (~11-15 degrees) than on younger Newhalen, Iliuk, and Ukak moraines (~18-20 degrees), indicating that a considerable length of time separated the Iliamna and Newhalen stades. Following late Wisconsin deglaciation of the Iliamna and Naknek lakes basins, lake levels lowered, creating a flight of wave-cut terraces. Horizontal terraces, formed during latest Wisconsin/early Holocene time, at ~40 m above Iliamna Lake, and ~15 and ~30 m above Naknek Lake, suggest that these shorelines are not tilted as a result of glacial-isostatic rebound or regional tectonism. Electron-microprobe analysis of six late Pleistocene tephra samples allows five samples to be correlated with latest Pleistocene Lethe tephra, and extends the Lethe ash plume ~125 km westward, and ~150 km northwestward of its presumed source area.

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