Identification of Tsunami Deposits in the Geologic Record: Developing Criteria Using Recent Tsunami Deposits
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Identification of Tsunami Deposits in the Geologic Record: Developing Criteria Using Recent Tsunami Deposits Robert Peters and Bruce Jaffe Open-File Report 2010-1239 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior KEN SALAZAR, Secretary U.S. Geological Survey Marcia K. McNutt, Director U.S. Geological Survey, Reston, Virginia 2010 For product and ordering information: World Wide Web: http://www.usgs.gov/pubprod Telephone: 1-888-ASK-USGS For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment: World Wide Web: http://www.usgs.gov Telephone: 1-888-ASK-USGS Suggested citation: Peters, Robert, and Jaffe, Bruce E., 2010, Identification of tsunami deposits in the geologic record; developing criteria using recent tsunami deposits: U.S. Geological Survey Open-File Report 2010-1239, 39 p. [http://pubs.usgs.gov/of/2010/1239/]. 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Contents Abstract ......................................................................................................................................................... 1 Introduction .................................................................................................................................................... 1 Sedimentary Characteristics of Recent Tsunami Deposits ............................................................................ 3 Deposit Thickness and Geometry .............................................................................................................. 3 Grain Size .................................................................................................................................................. 6 Large Grain Sizes (Granules, Pebbles, Cobbles, Boulders) ................................................................... 6 Grading................................................................................................................................................... 8 Grain Size Statistics ............................................................................................................................. 10 Layers ...................................................................................................................................................... 11 Contacts ................................................................................................................................................... 11 Surface Features...................................................................................................................................... 12 Grain Surface Texture .............................................................................................................................. 12 Composition ............................................................................................................................................. 13 Organic Material ....................................................................................................................................... 14 Shells ....................................................................................................................................................... 14 Foraminifera and Diatoms ........................................................................................................................ 14 Sedimentary Structures and Other Characteristics .................................................................................. 15 Depositional Environments .......................................................................................................................... 16 Preservation................................................................................................................................................. 18 Developing Tsunami Deposit Identification Criteria ..................................................................................... 20 Conclusions ................................................................................................................................................. 22 Acknowledgements ...................................................................................................................................... 23 References Cited ......................................................................................................................................... 23 Appendix ...................................................................................................................................................... 28 Figures Figure 1. World map showing the locations of recent tsunami deposits used in this study and in the Recent Tsunami Deposit Database ......................................................................................................... 3 Figure 2. Topographic profile, tsunami deposit thickness, and tsunami flow depths and elevations at Jantang, Sumatra, Indonesia, following the December 26, 2004 tsunami ........................................... 4 Figure 3. Photos of recent tsunami deposits showing deposit characteristics ......................................... 6 Figure 4. La Quinta, Peru; June 23, 2001 tsunami .................................................................................. 8 Figure 5. Basalt boulder transported by the December 29, 2010 tsunami in Samoa. Photograph courtesy of Bruce Richmond. .................................................................................................................. 9 Figure 6. La Quinta, Peru; June 23, 2001 tsunami ................................................................................ 10 Figure 7. Mud cracks at surface of tsunami deposit at Kuala Meurisi, Sumatra, Indonesia. December 26, 2004 tsunami ................................................................................................................. 13 Figure 8. A marsh at Lhok Kruet, Sumatra, Indonesia, coseismically subsided and submerged by the December 26, 2004 earthquake and inundated by the tsunami ...................................................... 20 iii Conversion Factors Inch/Pound to SI Multiply By To obtain Length inch (in.) 2.54 centimeter (cm) inch (in.) 25.4 millimeter (mm) foot (ft) 0.3048 meter (m) mile (mi) 1.609 kilometer (km) yard (yd) 0.9144 meter (m) Mass ounce, avoirdupois (oz) 28.35 gram (g) pound, avoirdupois (lb) 0.4536 kilogram (kg) ton, short (2,000 lb) 0.9072 megagram (Mg) ton, long (2,240 lb) 1.016 megagram (Mg) SI to Inch/Pound Multiply By To obtain Length centimeter (cm) 0.3937 inch (in.) millimeter (mm) 0.03937 inch (in.) meter (m) 3.281 foot (ft) kilometer (km) 0.6214 mile (mi) meter (m) 1.094 yard (yd) Mass gram (g) 0.03527 ounce, avoirdupois (oz) kilogram (kg) 2.205 pound avoirdupois (lb) megagram (Mg) 1.102 ton, short (2,000 lb) megagram (Mg) 0.9842 ton, long (2,240 lb) iv Identification of Tsunami Deposits in the Geologic Record: Developing Criteria Using Recent Tsunami Deposits Robert Peters and Bruce Jaffe Abstract There is a need for a clear procedure to identify tsunami deposits in the geologic record. Data from published studies documenting recent tsunami deposits provide a means of developing identification criteria based on the sedimentary characteristics of unequivocal tsunami deposits. Recent tsunami deposits have many sedimentary characteristics in common. All had sharp or erosional basal contacts. Sand was typically deposited in sheets that blanketed pre-existing topography and generally thinned landward. Deposit thickness was dependent on local topography; deposits were thicker in swales or local depressions and thinner on ridges or topographic highs. Deposits typically had 1-4 layers. Normal grading was common and often confined to individual layers. In muddy environments, sediments contained mud and soil rip-up clasts and mud often capped the deposits or layers. Boulders were often present, either isolated or scattered in groups. Sedimentary structures were rare, and included cross-bedding, laminations, scour and fill structures, and truncated flame structures. The composition, grain size, and surface texture of the grains reflected the coastal and nearshore source for the sediments. These sedimentary characteristics are the basis for developing site-specific tsunami deposit identification criteria that can be used in paleotsunami deposits investigations. Introduction Recent tsunamis, including the February 27, 2010 Chile tsunami (Morton and others, 2010), the September 29, 2009, Samoa-Tonga tsunami (Lay and others, 2010) and the December 12, 2004, Indian Ocean tsunami (Lay and others, 2005; Titov and others, 2005), have emphasized the need to assess tsunami hazards worldwide to help mitigate the impacts, including loss of life and property and damage to cities, communities and infrastructure, that these events can bring. Over the last two decades, tsunami deposit investigations have become a key component in efforts to evaluate tsunami risk to communities. Tsunami deposits are often used in the evaluation of tsunami hazard. Tsunami hazard maps use tsunami deposits to validate and to expand on the results of tsunami inundation modeling (Priest and others, 1997;