A Holocene Stratigraphic Record from Chirikof Island, Alaska Alan R
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University of Rhode Island DigitalCommons@URI Geosciences Faculty Publications Geosciences 2015 Tsunami recurrence in the eastern Alaska-Aleutian arc: A Holocene stratigraphic record from Chirikof Island, Alaska Alan R. Nelson Richard W. Briggs See next page for additional authors Creative Commons License Creative Commons License This work is licensed under a Creative Commons Attribution 4.0 License. Follow this and additional works at: https://digitalcommons.uri.edu/geo_facpubs Citation/Publisher Attribution Nelson, A.R., Briggs, R.W., Dura, T., Engelhart, S.E., Gelfenbaum, G., Bradley, L.-A., Forman, S.L., Vane, C.H., and Kelley, K.A., 2015, Tsunami recurrence in the eastern Alaska-Aleutian arc: A Holocene stratigraphic record from Chirikof Island, Alaska: Geosphere, v. 11, no. 4, p. 1172–1203, doi:10.1130/GES01108.1. Available at: https://doi.org/10.1130/GES01108.1 This Article is brought to you for free and open access by the Geosciences at DigitalCommons@URI. It has been accepted for inclusion in Geosciences Faculty Publications by an authorized administrator of DigitalCommons@URI. For more information, please contact [email protected]. Authors Alan R. Nelson, Richard W. Briggs, Tina Dura, Simon E. Engelhart, Guy Gelfenbaum, Lee-Ann Bradley, Steve L. Forman, Christopher H. Vane, and Katherine A. Kelley This article is available at DigitalCommons@URI: https://digitalcommons.uri.edu/geo_facpubs/28 Research Paper GEOSPHERE Tsunami recurrence in the eastern Alaska-Aleutian arc: A Holocene stratigraphic record from Chirikof Island, Alaska GEOSPHERE; v. 11, no. 4 Alan R. Nelson1, Richard W. Briggs1, Tina Dura2, Simon E. Engelhart 3, Guy Gelfenbaum4, Lee-Ann Bradley1, Steve L. Forman5, Christopher H. Vane6, and Katherine A. Kelley7 doi:10.1130/GES01108.1 1Geologic Hazards Science Center, U.S. Geological Survey, Golden, Colorado 80401, USA 2Sea Level Research, Department of Marine and Coastal Science, Rutgers University, New Brunswick, New Jersey 08901, USA 12 figures; 4 tables; 1 supplemental file 3Department of Geosciences, University of Rhode Island, Kingston, Rhode Island 02881, USA 4Pacific Coastal and Marine Science Center, U.S. Geological Survey, Santa Cruz, California 95060, USA 5Department of Geology, Baylor University, Waco, Texas 76798-7354, USA CORRESPONDENCE: [email protected] 6British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK 7Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island 02882, USA CITATION: Nelson, A.R., Briggs, R.W., Dura, T., Engelhart, S.E., Gelfenbaum, G., Bradley, L.-A., Forman, S.L., Vane, C.H., and Kelley, K.A., 2015, Tsunami recurrence in the eastern Alaska-Aleutian ABSTRACT earthquakes. If so, the Semidi segment of the Alaska-Aleutian megathrust arc: A Holocene stratigraphic record from Chirikof near Chirikof Island probably sent high tsunamis southward every 180–270 yr Island, Alaska: Geosphere, v. 11, no. 4, p. 1172–1203, doi:10.1130/GES01108.1. Despite the role of the Alaska-Aleutian megathrust as the source of some for at least the past 3500 yr. of the largest earthquakes and tsunamis, the history of its pre–twentieth Received 24 July 2014 century tsunamis is largely unknown west of the rupture zone of the great Revision received 23 April 2015 (magnitude, M 9.2) 1964 earthquake. Stratigraphy in core transects at two INTRODUCTION Accepted 11 June 2015 boggy lowland sites on Chirikof Island’s southwest coast preserves tsunami Published online 1 July 2015 deposits dating from the postglacial to the twentieth century. In a 500-m-long As a result of twenty-first century earthquakes of unexpected magnitude basin 13–15 m above sea level and 400 m from the sea, 4 of 10 sandy to silty (M; e.g., 2004 M 9.2 Sumatra-Andaman; 2011 M 9.0 Tohoku-Oki, Japan), ac- beds in a 3–5-m-thick sequence of freshwater peat were probably deposited companied by tsunamis of unanticipated height, much has been written by tsunamis. The freshwater peat sequence beneath a gently sloping alluvial about the need for assessments of tsunami hazards at subduction zones (e.g., fan 2 km to the east, 5–15 m above sea level and 550 m from the sea, con- Dominey-Howes et al., 2006; Dawson and Stewart, 2007; Satake and Atwater, tains 20 sandy to silty beds deposited since 3.5 ka; at least 13 were probably 2007; Shennan et al., 2009; Goto et al., 2011; Butler, 2012; Goff et al., 2012; deposited by tsunamis. Although most of the sandy beds have consistent Ryan et al., 2012a; Szczuciński et al., 2012; Satake, 2014). The most comprehen- thicknesses (over distances of 10–265 m), sharp lower contacts, good sorting, sive assessments are based on earthquake and tsunami histories that span and/or upward fining typical of tsunami deposits, the beds contain abundant multiple cycles of strain accumulation and release on the megathrust faults of freshwater diatoms, very few brackish-water diatoms, and no marine diatoms. subduction zones, that is, over many hundreds to thousands of years. Even in Apparently, tsunamis traveling inland over low dunes and boggy lowland en- Japan, where extensive written records of earthquakes and tsunamis extend trained largely freshwater diatoms. Abundant fragmented diatoms, and lake back more than a millennium, reconstructing the history of the greatest earth- species in some sandy beds not found in host peat, were probably trans- quakes and tsunamis requires thorough study of coastal stratigraphic archives OLD G ported by tsunamis to elevations of >10 m at the eastern site. Single-aliquot (e.g., Minoura et al., 2001; Witter et al., 2003; Cisternas et al., 2005; Bourgeois regeneration optically stimulated luminescence dating of the third youngest et al., 2006; Shennan and Hamilton, 2006; Nanayama et al., 2007; Jankaew bed is consistent with its having been deposited by the tsunami recorded at et al., 2008; Monecke et al., 2008; Sawai et al., 2012). Russian hunting outposts in 1788, and with the second youngest bed being One of the shortest and most incomplete histories of megathrust earth- OPEN ACCESS deposited by a tsunami during an upper plate earthquake in 1880. We infer quakes and tsunamis comes from one of the longest and most seismically from stratigraphy, 14C-dated peat deposition rates, and unpublished analyses active subduction zones, the Alaska-Aleutian arc, extending 1600 km from of the island’s history that the 1938 tsunami may locally have reached an southeast Alaska westward to Kamchatka (Fig. 1A; Nishenko and Jacob, 1990; elevation of >10 m. As this is the first record of Aleutian tsunamis extending Vallier et al., 1994; Carver and Plafker, 2008; Ryan et al., 2012b; Ruppert et al., throughout the Holocene, we cannot estimate source earthquake locations 2013; Butler et al., 2014; Shennan et al., 2014b). That the Aleutian arc is capable or magnitudes for most tsunami-deposited beds. We infer that no more than of sending damaging tsunamis across the Pacific basin is illustrated by those This paper is published under the terms of the 3 of the 23 possible tsunamis beds at both sites were deposited following produced by the series of mid-twentieth century M 8–9 ruptures in the central CC-BY license. upper plate faulting or submarine landslides independent of megathrust and eastern Aleutian arc, in 1946, 1957, 1964, and 1965 (Butler, 2012; Ross et al., © 2015 Geological Society of America GEOSPHERE | Volume 11 | Number 4 Nelson et al. | Holocene tsunami recurrence on Chirikof Island, Alaska Downloaded from https://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/4/1172/3335336/1172.pdf 1172 by University of Rhode Island user on 13 May 2019 Research Paper 155.7°155.6°W C 55.9°N 012345 km moraine GPS Southwest AC13 Anchorage 180° 160° 140°W Area 55.8 Figure 1. (A) Location of Chirikof Island within the plate of Fig.2 tectonic setting of the Alaska-Aleutian subduction zone. A ° Rupture areas for great twentieth century earthquakes CANADA on the megathrust are in pink. (B) Velocity field of the N US Alaska Peninsula and the eastern Aleutian Islands ob- A 70° New Ranch ALASKA valley served by global positioning system (GPS) (Fournier and Frey mueller, 2007). Colors show inferred rupture areas for a Fairbanks earthquakes in 1788 (green) and 1938 (orange). Both A fault scarp and B are modified from Witter et al. (2014). The section of Bering Se the megathrust between Kodiak Island and the Shumagin 65° Anchorage Islands has been referred to as the Semidi segment (e.g., Shennan et al., 2014b). (C) Physiography of Chirikof 164° 162° 58°N Island (Google Earth image, 2012) showing the location 1964 of our study area at Southwest Anchorage, a prominent Area Chirikof of B moraine, a fault scarp (facing southeast) that probably 60° Island B st records the 1880 earthquake, the New Ranch valley re- 8 ru ds th slan 193 a Island connaissance core site, and UNAVCO GPS station AC13 ian I eg Alaska ak Aleut m di (http:// pbo .unavco .org /station /overview /AC13). In the 1946 ian leut Ko 1957 A Gulf of eighteenth and nineteenth centuries, Chirikof Island was Sitkalidak known to native Alutiiq and Russians as Ukamuk Island. Island Three 5.3 mm/yr Saints Bay Bering Block motion Sitkinak t Island Rupture areas of the 56° Pavlof 1788 earthquakes? Cold Bay gin s Chirikof Shumand Semidi segmen Isla Island Unga Rupture area of the Island 1938 earthquake? Simeonof Sanak Island Island 0 50 100 63 mm/yr km 54° Pacific Plate motion 162° 160° 158° 156° 154°W GEOSPHERE | Volume 11 | Number 4 Nelson et al. | Holocene tsunami recurrence on Chirikof Island, Alaska Downloaded from https://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/4/1172/3335336/1172.pdf 1173 by University of Rhode Island user on 13 May 2019 Research Paper 2013). Based on historical records, a tsunami-source statistical analysis shows tigraphy reported here show that the southwest coast of the island has been that the source contributing the most to the tsunami hazard for Los Angeles glaciated, but was ice free by 13.4 ka.