HR: 14:25h
AN: OS13B-04    [Abstracts]
TI: Tephrochronologic Dating and Correlation of Historic and Prehistoric Tsunami Deposits in South-Central Alaska
AU: * Beget, J E
EM: ffjeb1@uaf.edu
AF: Geophysical Institute, University of Alaska-Fairbanks, Fairbanks, Ak. 99775-5760, United States
AU: Combellick, R A
EM: rod@dnr.state.ak.us
AF: Alaska Div. Geologic Geophysical Surveys, 794 University Ave. #200, Fairbanks, Ak 99709, United States
AU: Addison, J
EM: ftjaa@uaf.edu
AF: Geophysical Institute, University of Alaska-Fairbanks, Fairbanks, Ak. 99775-5760, United States
AB: Volcanic Ash deposits can be used to identify, date and correlate tsunami deposits in the Cook Inlet and Prince William Sound areas of south-central Alaska. The 1964 Good Friday Earthquake (M9.2) produced a major regional tsunami that affected the entire coast of south-central Alaska, and coeval submarine landslides in Prince William Sound generated local tsunamis more than 30 m high. The 1964 tsunami deposits on Augustine Island in Cook Inlet are partly buried by tephras and pyroclastic flows from recent eruptions and record an 8-m-high wave. Tsunami deposits recording a volcanic tsunami produced by an eruption at Augustine Volcano in 1883 indicate initial wave heights of more than 18 m, and are overlain by coeval 1883 tephra and also Katmai 1912 tephra at multiple sites on Augustine Island, as well as at Nanwalek and Homer 80-100 km to the north. Newly discovered tsunami deposits recording the penultimate great earthquake on the subduction zone beneath south- central Alaska are dated to ca. 950 yr BP near Valdez. The tsunami deposits are overlain by a mafic tephra from the Wrangell area erupted ca. 750 yr BP. The tephra and new dates on the tsunami deposit help refine the age of the late major earthquake on the subduction zone beneath south-central Alaska, as there is wide range of radiocarbon dates associated with broadly coeval episodes of local subsidence identified at sites in Prince William Sound and Cook Inlet. A regionally extensive Augustine tephra erupted ca. 800 yr BP occurs in sediments deposited after the subsidence at several sites around Cook Inlet, and further helps refine the age of the penultimate great earthquake in south-central Alaska. An older tsunami deposit located near Homer is dated to ca. 3400 yr BP and occurs above tephra from Redoubt Volcano, and records an older subduction zone earthquake. A still older tsunami deposit dated to 3600 yr BP directly underlies the Redoubt tephra, and may have been generated by a huge eruption at Redoubt Volcano that sent a large debris avalanche into Cook Inlet at that time.
DE: 1145 Tephrochronology (8455)
DE: 3070 Submarine landslides
DE: 4564 Tsunamis and storm surges
DE: 8494 Instruments and techniques
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting