Backwash sediment record of the 2009 South Pacific Tsunami and 1960 Great Chilean Earthquake Tsunami
|Author(s)||Riou Brieuc1, 2, Chaumillon Eric1, Chagu Catherine3, Sabatier Pierre4, Schneider Jean-Luc2, Walsh John-Patrick5, Zawadzki Atun6, Fierro Daniela6|
|Affiliation(s)||1 : Univ La Rochelle, CNRS, UMR 7266, LIENSs, F-17000 La Rochelle, France.
2 : Univ Bordeaux, CNRS, UMR 5805, EPOC, F-33615 Pessac, France.
3 : UNSW, Sch Biol Earth & Environm Sci, Sydney, NSW 2052, Australia.
4 : Univ Grenoble Alpes, Univ Savoie Mt Blanc, CNRS, EDYTEM,UMR 5204, F-73000 Chambery 73000, France.
5 : Univ Rhodes Isl, Narragansett, RI 02882 USA.
6 : Australian Nucl Sci & Technol Org, Lucas Heights, NSW 2234, Australia.
|Source||Scientific Reports (2045-2322) (Nature Publishing Group), 2020-03 , Vol. 10 , N. 1 , P. 4149 (13p.)|
|WOS© Times Cited||4|
Following recent tsunamis, most studies have focused on the onshore deposits, while the offshore backwash deposits, crucial for a better understanding of the hydrodynamic processes during such events and offering an opportunity for sedimentary archives of past tsunamis, have mostly been omitted. Here, we present a unique sedimentary record of the backwash from two historical tsunamis sampled in a sheltered bay in American Samoa, namely the 2009 South Pacific Tsunami and the 1960 Great Chilean Earthquake Tsunami. Although not always concomitant with a marked grain size change, backwash deposits are identified by terrestrial geochemical and mineralogical signatures, associated with basal soft sediment micro-deformations. These micro-deformations, including asymmetric flame structures, are described for the first time in historic shallow marine backwash deposits and lead us to propose an improved depositional mechanism for tsunami backflow based on hyperpycnal currents. Moreover, this study brings a potential new criterion to the proxy toolkit for identifying tsunami backwash deposits, namely the basal soft sediment micro-deformations. We suggest that further studies focus on these micro-deformations in order to test the representability of this criterion for tsunami backwash deposits. Sheltered shallow marine environments in areas repeatedly impacted by tsunamis have a higher potential for the reconstruction of paleo-tsunami catalogs and should be preferentially investigated for coastal risk assessment.