TY - JOUR T1 - Sedimentary evidence of prehistoric distant‐source tsunamis in the Hawaiian Islands JF - Sedimentology Y1 - 2020 A1 - La Selle, SeanPaul A1 - Richmond, Bruce M. A1 - Jaffe, Bruce E. A1 - Nelson, Alan R. A1 - Griswold, Frances R. A1 - Arcos, Maria E. M. A1 - Chagué, Catherine A1 - Bishop, James M. A1 - Bellanova, Piero A1 - Kane, Haunani H. A1 - Lunghino, Brent D. A1 - Gelfenbaum, Guy ED - Costa, Pedro KW - Aleutians KW - deposit KW - distant source KW - extreme events KW - Hawai΄i KW - palaeotsunami AB - Over the past 200 years of written records, the Hawaiian Islands have experienced tens of tsunamis generated by earthquakes in the subduction zones of the Pacific ‘Ring of Fire’ (for example, Alaska–Aleutian, Kuril–Kamchatka, Chile and Japan). Mapping and dating anomalous beds of sand and silt deposited by tsunamis in low‐lying areas along Pacific coasts, even those distant from subduction zones, is critical for assessing tsunami hazard throughout the Pacific basin. This study searched for evidence of tsunami inundation using stratigraphic and sedimentological analyses of potential tsunami deposits beneath present and former Hawaiian wetlands, coastal lagoons, and river floodplains. Coastal wetland sites on the islands of Hawai΄i, Maui, O΄ahu and Kaua΄i were selected based on historical tsunami runup, numerical inundation modelling, proximity to sandy source sediments, degree of historical wetland disturbance, and breadth of prior geological and archaeological investigations. Sand beds containing marine calcareous sediment within peaty and/or muddy wetland deposits on the north and north‐eastern shores of Kaua΄i, O΄ahu and Hawai΄i were interpreted as tsunami deposits. At some sites, deposits of the 1946 and 1957 Aleutian tsunamis are analogues for deeper, older probable tsunami deposits. Radiocarbon‐based age models date sand beds from three sites to ca 700 to 500 cal yr bp, which overlaps ages for tsunami deposits in the eastern Aleutian Islands that record a local subduction zone earthquake. The overlapping modelled ages for tsunami deposits at the study sites support a plausible correlation with an eastern Aleutian earthquake source for a large prehistoric tsunami in the Hawaiian Islands. VL - 67 UR - https://onlinelibrary.wiley.com/doi/10.1111/sed.12623 IS - 3 ER - TY - JOUR T1 - Evidence for frequent, large tsunamis spanning locked and creeping parts of the Aleutian megathrust JF - GSA Bulletin Y1 - 2019 A1 - Witter, Rob A1 - Briggs, Rich A1 - Engelhart, Simon E. A1 - Gelfenbaum, Guy A1 - Koehler, Rich D. A1 - Nelson, Alan A1 - Selle, SeanPaul La A1 - Corbett, Reide A1 - Wallace, Kristi AB - At the eastern end of the 1957 Andreanof Islands, Alaska, USA, moment magnitude 8.6 earthquake rupture, Driftwood Bay (Umnak Island) and Stardust Bay (Sedanka Island) lie along presently locked and creeping parts of the Aleutian megathrust, respectively, based on satellite geodesy onshore. Both bays, located 200 km apart, face the Aleutian trench and harbor coastal evidence for tsunami inundation in 1957. Here we describe the evidence at Driftwood Bay, including eight sheets of landward-fining, normally-graded marine sand that extend up to 375 m inland and 23 m above mean tide level. Drift logs that corroborate historical accounts of 1957 tsunami runup on Umnak Island’s Pacific coast overlie the youngest sand sheet, which 137Cs activity shows was deposited in the decade before 1963. The older sand sheets probably record tsunamis prior to 1957 because an emergent coastal terrace lacks evidence for storm-wave erosion and overwash since ca. 2 ka. Comparisons of the Driftwood Bay and Stardust Bay tsunami histories suggest that at least twice in the past 1700 years inundation occurred at one site but not the other. In contrast, Bayesian age-depth modeling suggests that the two bays may record five tsunamis like the 1957 tsunami, generated by earthquake ruptures that spanned the presently locked and creeping parts of the Aleutian megathrust. However, serial tsunamis occurring within days to centuries cannot be precluded. Our findings imply 164–257-year recurrence intervals for large eastern Aleutian tsunamis and challenge the notion that creeping parts of the megathrust, inferred from geodesy onshore, pose lower earthquake and tsunami hazards than locked areas. VL - 131 UR - https://pubs.geoscienceworld.org/gsa/gsabulletin/article/131/5-6/707/566656/Evidence-for-frequent-large-tsunamis-spanning IS - 5-6 ER - TY - DATA T1 - Radiocarbon, Cesium-137, Grain Size, and X-ray Fluorescence Data for Tsunami Geology Investigation, Driftwood Bay, Umnak Island, Alaska (2018) Y1 - 2018 A1 - Witter, Rob A1 - Gelfenbaum, Guy A1 - Corbett, Reide A1 - Tam, Angela A1 - La Selle, SeanPaul AB - These files provide the complete data release for the paper entitled, "Frequent large tsunamis spanned locked/creeping parts of the Aleutian megathrust." The data set consists of nine tables that include radiocarbon dates, cesium-137 activity, grain size measurements, and scanning X-ray fluorescence element intensity counts. PB - Alaska Science Center, U.S. Geological Survey UR - https://doi.org/10.5066/P9D7KLJV ER - TY - JOUR T1 - Unusually large tsunamis frequent a currently creeping part of the Aleutian megathrust JF - Geophysical Research Letters Y1 - 2016 A1 - Witter, Robert C. A1 - Carver, Gary A. A1 - Briggs, Richard W. A1 - Gelfenbaum, Guy A1 - Koehler, Richard D. A1 - La Selle, SeanPaul A1 - Bender, Adrian M. A1 - Engelhart, Simon E. A1 - Hemphill-Haley, Eileen A1 - Hill, Troy D. AB - Current models used to assess earthquake and tsunami hazards are inadequate where creep dominates a subduction megathrust. Here we report geological evidence for large tsunamis, occurring on average every 300–340 years, near the source areas of the 1946 and 1957 Aleutian tsunamis. These areas bookend a postulated seismic gap over 200 km long where modern geodetic measurements indicate that the megathrust is currently creeping. At Sedanka Island, evidence for large tsunamis includes six sand sheets that blanket a lowland facing the Pacific Ocean, rise to 15 m above mean sea level, contain marine diatoms, cap terraces, adjoin evidence for scour, and date from the past 1700 years. The youngest sheet and modern drift logs found as far as 800 m inland and >18 m elevation likely record the 1957 tsunami. Previously unrecognized tsunami sources coexist with a presently creeping megathrust along this part of the Aleutian Subduction Zone. VL - 43 UR - http://doi.wiley.com/10.1002/2015GL066083 IS - 1 ER -