Date of Award:
Master of Science (MS)
This study focuses on the late-Wisconsin Brooks Lake glaciation, lake-level fluctuations, and volcanic deposits in the lliarnna/Naknek/Brooks Lake area on the northern Alaska Peninsula, southwestern Alaska. The Brooks Lake glaciation consists of five stades, from youngest to oldest: Kvichak, Uiarnna, 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, lliarnna stade, or both. The presence in the Iliamna Lake valley, and the absence in the Naknek Lake valley of a two-fold 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. Plant macrofossils dated at 26,155 ± 285 I4C yr BP afford a new maximum-limiting age on the type Kvichak moraine. Slope angles on the type Kvichak and Iliamna moraines are less steep (~11-15°) than on younger Newhalen, lliuk, and Ukak moraines (~18-20° ), indicating that a considerable length of time separated the Iliamna and Newhalen stades. Correlation of this time-stratigraphic marker with other better dated Alaskan glacial sequences suggests that the interstadial occurred -13-14 ka. Following late-Wisconsin de glaciation of the Iliamna and Naknek lake 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. The most prominent terraces above both lakes lay about halfway between the highest terrace and present-day lake level. If these terraces are correlative, then this indicates some climate control on lake-level fluctuations. 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. Analysis of four early-Holocene black tephras fails to support any correlations, suggesting that there are multiple black tephras in the area. Ash C, a tricolored ash, consists of more than one chemically distinct tephra, and there is little consistency between color zones of the ash at different sites.
Stilwell, Karen B., "Late Quaternary Glacial Geology, Shoreline Morphology, and Tephrochronology of the lliamna/Naknek/Brooks Lake Area, Southwestern Alaska" (1995). All Graduate Theses and Dissertations. 6595.
Copyright for this work is retained by the student. If you have any questions regarding the inclusion of this work in the Digital Commons, please email us at .