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  3. Grain size distribution analysis of soils, tephras, and culturally-modified sediments record prehistoric human resilience to geologic processes in the Islands of Four Mountains, AK
Title

Grain size distribution analysis of soils, tephras, and culturally-modified sediments record prehistoric human resilience to geologic processes in the Islands of Four Mountains, AK

    Item Description
    Limited Access
    The author(s) chose to restrict access to this thesis to current Whitman students, faculty, and staff. Please log in to view it.
    Linked Agent
    Creator (cre): Mazzoleni, Caitlin Marie
    Advisor (adv): Nicolaysen, Kirsten
    Department (dpt): Whitman College. Geology - Environmental Studies
    Date
    May 8, 2019
    Graduation Year
    2019
    Abstract

    The Holocene coastal environment of the Islands of Four Mountains (IFM), in the east-central Aleutian Archipelago, is prone to volcanism, earthquakes, tsunamis, changing sea levels, glaciation, and paraglacial processes that have challenged long-term human occupation. From circa 3,800 cal yr BP until 1741 CE, the Unangax (Aleut) people lived on sediment fans of debris flows on Carlisle and Chuginadak Islands. 86 samples from three stratigraphic profiles were collected from beach cliffs eroded from alluvial/paraglacial fan toes. Two sample profiles intersected prehistoric village sites (AMK-0003 Unit 3, n=32; AMK-0003 Unit 4, n=42), and one consisted of a comparative profile of undisturbed volcanic ashes (CR-N, n=12). Grain size analyses of the fine sediment fraction combined with archaeological records and field observations permits attribution of one or more emplacement or alteration processes (such as debris flow, airfall tephra, human modified, etc.) involved with each layer of strata. The base of the fans are composed primarily of debris flow deposits associated with paraglacial conditions. Overlying fine-grained layers (collectively up to 3 m thick) are associated with tephra, fluvial, and cultural deposition. Cultural layers were identified by features such as artifactual materials, charcoal lenses, and chipped stone tools. Grain size distributions (GSD) for basal, non-volcanic debris flow deposits show bimodal or unimodal peaks with a broad distribution of grain size (mode range: 33.1-665 µm, D10: 6.06-19.48 µm, and a D90: 90.7-834 µm). Layers interpreted as volcanic air-fall ashes show defined unimodal peaks with either a fine skew or coarse skew (mode range: 48-923 µm, D10: 13-42 µm, and a D90: 196-1470 µm). Some tephra layers were interpreted as pyroclastic density currents (PDCs) (mode range: 211-923 µm, D10: 6.95-42.4 µm, and a D90: 440-1470 µm). Analyses of these data reveal information about source proximity and explosivity of volcanic events. Twelve culturally-modified strata feature distinctly broad, flat-topped peaks that are slightly bimodal in GSD (mode range: 49-439 µm, D10 range: 16-21 µm, D90 range: 465-694 µm, kurtosis: 2.921-14.826). These data show evidence of human occupation during periodic volcanic eruptions and reoccupation after displacement by a larger eruption (ca. 1,050 BP), illustrating the resilience of the people who inhabited these islands.

    Subject
    Soils -- Analysis
    Volcanic ash, tuff, etc.
    Sediments (Geology)
    Resilience (Personality trait)
    Geology, Stratigraphic -- Paleocene
    Geology, Stratigraphic -- Holocene
    Pleistocene-Holocene boundary
    Science
    Environmental sciences
    Academic theses
    Whitman College 2019 -- Dissertation collection -- Geology-Environmental Studies
    Geographic Subject
    United States
    Alaska
    Four Mountains, Islands of (Alaska)
    Genre
    Theses
    Extent
    54 pages
    Permanent URL
    http://works.whitman.edu/2019040
    Rights
    http://rightsstatements.org/vocab/InC/1.0/
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    THESIS_2019_1102362944_001
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