With a minimum of three reported waves, the 2011 Tohoku-oki tsunami’s destructive force caused massive damage along the northern Japanese Aomori coast. At Misawa the coastal control area was inundated up to 550 m inland and sandy sediment remnants can be traced to c. 350 m (c. 61–63% of the maximum inundation) from the shoreline. Linking the discovery of floatable plastic objects within a woody and organic layer to our analytical data lead to the detection of a yet undocumented woody-organic tsunami deposit first appearing on top of the sandy deposit but then reaching even further inland (approx. 69–72% of the max. inundation). By this observation our understanding of the documented part of the tsunami inundation may be improved. As a consequence, sand sheets of historic and paleo-tsunamis represent minimum estimates for the coastal inundation and underestimation may be reduced by addressing the woody and organic fraction of a tsunami’s inundation.
Far‐field tsunami deposits observed in the Kahana Valley, O‘ahu, Hawai‘i (USA), were investigated for their organic‐geochemical content. During short high‐energy events, (tsunamis and storms) organic and chemical components are transported with sediment from marine to terrestrial areas. This study investigates the use of anthropogenic based organic geochemical compounds (such as polycyclic aromatic hydrocarbons, pesticides and organochlorides) as a means to identify tsunami deposits. Samples were processed by solid–liquid extraction and analyzed using gas chromatography–mass spectrometry. A total of 21 anthropogenic marker compounds were identified, of which 11 compounds were selected for detailed analysis. Although the tsunami deposits pre‐date industrial activity in Hawai‘i by several hundred years, distinct changes were found in the concentrations of anthropogenic marker compounds between sandy tsunami deposits and the surrounding mud/peat layers, which may help in identifying tsunami deposits within cores. As expected, low overall concentrations of anthropogenic markers and pollutants were observed due to the lack of industrial input‐sources and little anthropogenic environmental impact at the study site. This geochemical characterization of tsunami deposits shows that anthropogenic markers have significant potential as another high‐resolution, multi‐proxy method for identifying tsunamis in the sedimentary record.
<p>In AD&#160;1755 a strong earthquake-generated tsunami destroyed large parts of the southwest Iberian coastline. Data for the study of the sedimentological characteristics and palaeo-ecological effects of the backwash of this well-known AD&#160;1755 Lisbon tsunami and possible preceding events on the continental shelf was obtained during RV METEOR cruise M152 in November 2018, since the hydrodynamics of tsunami backwash currents are as yet poorly understood. Furthermore, the suitability of the shelf as a reliable sedimentary archive for tsunami deposits was investigated.</p><p>Along the Algarve coast, prominent AD&#160;1755 Lisbon tsunami deposits have been detected onshore for quite some time. Cruise M152 conducted a geophysical survey on the corresponding shelf area to obtain bathymetry and sub-bottom profiles for the recognition of depositional basins. Subsequently, 19 sediment cores were retrieved from the most suitable depositional basins by vibracoring at water depths from 65 to 114&#160;m. The cores were analysed in a multiproxy approach (granulometry, magnetic susceptibility, P-wave velocities, organic and inorganic geochemistry, micropalaeontology). Deposits of the AD&#160;1755 Lisbon tsunami were identified in most of the cores as a thin layer at ca. 20&#160;cm depth.</p><p>More surprisingly, a second event deposit dating to ca.&#160;3700&#160;years&#160;cal.&#160;BP was detected at core depths of 122 to 155&#160;cm. It is even traceable in the sub-bottom profiles and consists of a distinctive ca. 30&#160;cm thick well sorted medium-sized siliciclastic sand. Due to the thickness of the deposit an in-depth study of its characteristics was possible. It displays an erosive basal contact followed by a thin matrix-poor shell hash layer, a reversely graded fine sand layer and ultimately a massive, quite homogeneous medium sand resembling the T<sub>a</sub> division of the Bouma sequence or the S<sub>1</sub>, S<sub>2</sub> and S<sub>3</sub> divisions of the Lowe sequence. The deposit is distinguishable from the silt to silty sand-dominated background sedimentation not only due to the textural and compositional features, but also due to contrasting geophysical and geochemical properties. Terrestrial provenance for (at least parts of) the sediment is revealed by biomarker analysis. Based on these characteristics, the deposit is interpreted as the result of a high density hyperpycnal flow from the coast towards the offshore caused by tsunami backwash. This event layer may be correlated to onshore observations of tsunami deposits along the southwest coast of Spain but has never been identified in Portugal where the onshore record of tsunami deposits only covers the last three millennia.</p><p>The results of this multiproxy analysis strongly suggest the shallow offshore area below storm wave base to host reliable sedimentary archives for tsunami backwash deposits, which allow the discovery of as yet unknown events. Palaeotsunami research can benefit from the investigation of offshore archives, especially where onshore records are incomplete or sparse.</p>
The 2011 Tohoku-oki tsunami left a characteristic geochemical signature in the sediments of the Misawa harbor on the Aomori coastline (northern Japan), not only in vertical stratigraphy but also in lateral distribution. Suitable indicator compounds for the tsunami impact were used to identify and characterize the distribution of geochemical patterns within the harbor area. Specific compounds are illustrating the different emission sources and distribution during the 2011 tsunami. Petrogenic-derived markers, such as hopanes and polycyclic aromatic hydrocarbons, provide information about the tsunami-related destruction of facilities and technical material and the subsequent release of, for instance, oil and grease. Linear alkylbenzenes and diisopropylnaphthalene are used to identify sewage-derived contaminants released by the tsunami. Old burden markers such as dichlorodiphenyltrichloroethane and its metabolites or polychlorinated biphenyl signal erosion and rearrangement of contaminants present in the sediments prior to the tsunami. Distribution of the analyzed pollutant groups indicate the tsunami-related release through various emission sources and their potential origin. While petrogenic-derived pollutants revealed a significant local spread with hotspot formation near the release, sewage-derived compounds were widely distributed and originated from a diffuse source not necessarily located in the harbor area. In contrast to freshly released contaminants, old burden markers are characterized by erosion of contaminated pre-tsunami sediment, the remobilization of pollutants and subsequent deposition of these sediment-bound contaminants in the tsunami layer. The correlation between all pollutant groups by their preferred accumulation reveals that source-specific compounds show different emission sources but reveal also a topographical control of the pollutant distribution by the 2011 tsunami.
<p>Organic geochemistry is commonly used in environmental studies. In tsunami research, however, its application is in its infancy and rarely used. Tsunami deposits may also be able to be characterized by organic-geochemical parameters as tsunami transports not only particulate sedimentary material from marine to terrestrial areas (and vice versa), but also associated organic material. Recently, more attention has been given to the usage of natural organic substances (biomarkers) for tsunami identification. We present results of biomarkers and anthropogenic markers detected in deposits of the 2011 Tohoku-oki tsunami on the Sendai Plain, Japan (Bellanova et al., 2020). As the tsunami inundated the coastal lowland up to 4.85&#160;km inland, sediments from various sources were eroded, transported and deposited across the area. This led to the distribution of biomarkers from different sources across the Sendai Plain creating a unique geochemical signature in the tsunami deposits. The tsunami also caused destruction along the Sendai coastline, leading to the release of large quantities of environmental pollutants (e.g., fossil fuels, tarmac, pesticides, plastics, etc.) that were distributed across the inundated area. Corresponding anthropogenic markers, represented by three main compound groups (polycyclic aromatic hydrocarbons, pesticides, and halogenated compounds), were preserved in tsunami deposits (at least until 2013, prior to land clearing). Organic compounds from the tsunami deposits (Tohoku-oki tsunami) were extracted from tsunami sediment and compared with the organic signature of unaffected pre-tsunami samples using gas chromatography-mass spectrometry (GS/MS) based analyses. Their concentrations differed significantly from the pre- and post-tsunami background contamination levels. Organic proxy concentrations differ also for sandy and muddy tsunami deposits due to various factors (e.g., preservation, dilution, microbial alteration).</p><p>As tsunami research advanced over the last decades so did the methods used to gain more and more information on the past events. Developing new methods for the identification and characterization of tsunami deposits for recent, historic or paleo events is crucial. Every piece of additional information we gain from event deposits leads us a step further to a better understanding of mechanisms acting during a tsunami. This will help to improve countermeasures and relief efforts. Anthropogenic markers and biomarkers, because of their high source specificity and good preservation potential, have the potential to be a valuable proxy in future studies of tsunami deposits and provide information about sediment sources and transport pathways.</p>
<p>With at least three reported waves, the 2011 Tohoku-oki tsunami&#8217;s destructive force caused massive damage along the Aomori coastline in northern Japan. At Misawa the coastal area was inundated up to 550&#160;m inland and sandy sediment remnants can be traced to c. 350&#160;m (c. 61-63% of the maximum inundation) from the shoreline.</p><p>The discovery of a floatable plastic object within a previously inconspicuous woody and organic layer in connection to our analytical data lead to the detection of a yet undocumented &#8216;invisible&#8217; tsunami deposit. This layer is first appearing on top of the sandy deposit but then reaching even further inland (approx. 69-72% of the max. inundation). Initially the organic and woody layer was not evident during early stages of the field work and this would have been unchanged without the discovery of the floatable plastic particle embedded within the deposit. That critical observation was the turning point for the interpretation of the layer&#8217;s origin and thus our understanding of processes during the Tohoku-oki tsunami at the Aomori coast near Misawa harbor. Overall, may the first recognition of this woody-organic and up to now &#8216;invisible&#8217; layer lead to an improvement in the understanding of tsunami processes and their sedimentological characteristics. Further, may the knowledge obtained from these types of deposits be transferred to and improve paleo-tsunami investigations, especially in rural natural environments, as sand sheets of historic and paleo-tsunamis represent minimum estimates for the coastal inundation and potential underestimations may be reduced by addressing the &#8216;invisible&#8217; fraction of a tsunami&#8217;s inundation.</p>
<p>Research on offshore tsunami deposits is scarce and their depositional processes and preservation potential are virtually unexplored. Therefore, the RV Meteor cruise M152 mapped and sampled one coast-parallel and two coast-perpendicular transects at water depths from 65 to 114&#160;m off the Algarve coast (Portugal). This coast was strongly affected by the well-known Lisbon earthquake and tsunami of November 1<sup>st</sup>, 1755&#160;AD. Numerous onshore locations have been well documented and studied with historic damage reports and modern scientific investigations of the onshore tsunami deposits. However, very scarce information about the backwash, the water masses flowing back into the sea, exists and their imprint on the shelf is unexplored.</p><p>In order to fill this gap, a total of 19 vibracores were recovered during the RV Meteor cruise M152. For tracing the sedimentary imprint of the AD 1755 tsunami and potential predecessors, a multi-proxy analysis was carried out (sedimentology, micropaleontology, inorganic and organic geochemistry, radiocarbon and OSL dating). Within the offshore Holocene stratigraphic record, at least two event layers of likely tsunami backwash origin were identified based on their significantly different properties compared to the background shelf sediments. The uppermost tsunami layer (at a depth of 16-25&#160;cm in most cores) displays an erosional contact at the base with heterogeneous compositional changes; its bounding radiocarbon ages allow a correlation with the AD&#160;1755 Lisbon tsunami. Organic-geochemical markers, such as n-alkanes, polycyclic aromatic hydrocarbons, steroids and fatty acids, show an increased input of terrestrial matter in this offshore AD 1755 event layer.</p><p>A surprising discovery was another distinct high-energy deposit, i.e. a potential predecessor to the AD&#160;1755 Lisbon tsunami, at a core depth of about 122-155&#160;cm, which was <sup>14</sup>C-dated to approx. 3700&#160;yrs&#160;cal BP. Due to its erosional base and coarse-grained composition (well-sorted medium sand), as well as the increased terrestrial influence (displayed by biomarkers), it can be assumed that this deposit originates from the backwash of a paleo-tsunami.</p><p>This multi-proxy approach with sedimentological, micropaleontological, inorganic and organic-geochemical criteria, enabled us to (1) identify of backwash tsunami deposits; (2) establish a recurrence interval; and (3) estimate the hazard potential for the related coastal areas. Results of the M152 cruise demonstrate for the first time that the depositional basins on the Algarve shelf have the potential to reliably archive Holocene tsunami backwash deposits. The low-energy environment of the outer Algarve shelf sets prime conditions for the preservation of tsunami backwash deposits. Thus, these geoarchives offer the possibility to study the mechanisms and hydrodynamics of backwash currents, and to investigate tsunami strata that are not preserved elsewhere.</p>
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.