Displays

Cyprus has a long record of tsunami waves, as noted by archaeological and geological records. Large boulder deposits have been noted in the southeastern and western part of the Island. At Cape Greco (southeastern Cyprus) large boulders have been noted, however, no detailed geomorphological research has taken place so far and the related high energy event remains undated. Our research focuses at Cape Greco Peninsula in order to record in detail and interpret the large boulders deposits. The boulders, located at 3 m amsl, are fragments of a layer of an upper Pleistocene aeolianite, which is overlaying unconformly a lower Pleistocene calcarenite. Dimensions and spatial distribution of 272 small, medium and large boulders were documented, while their precise distance from the coastline was recorded by field mapping and remote sensing, using GNSS, drone and GIS technics. Several large boulders weighting more than ~30 metric tons were found up to 60m inland. Geomorphologic mapping and morphometric measurements, along with the presence of marine organisms suggests that some of the boulders were removed from their original intertidal zone and were transported inland by the force of large waves. In this work, we attempt to determine the extreme event that caused their transport inland. We further attempt a correlation of the event with already known tsunami events from Eastern Mediterranean, based on the estimated wave heights and the radiocarbon dating of marine gastropods (Vermetus sp.).

How to cite: Evelpidou, N., Zerefos, C., Synolakis, C., Repapis, C., Karkani, A., Polidorou, M., and Saitis, I.: Boulder deposits on the southeastern coast of Cyprus and their relation with paleotsunami events of the Eastern Mediterranean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19736, https://doi.org/10.5194/egusphere-egu2020-19736, 2020.

Tsunami geoscience has evolved greatly since its seminal works in late 1980’s. Initially, tsunami deposits were merely identified in the stratigraphic record using its singularity and penetration inland. Later, especially after the 2004 and 2011 tsunami events, recognition of tsunami deposits progressed to interpretation on sediment dynamics and inundation phases based on the progressive application of different sedimentological, geochemical, paleontological and geophysical analytical techniques. Equally to other locations worldwide, tsunami deposits in Portugal were originally (early 1990’s) identified due to its geomorphological imprint or by its coarser sandy nature in muddy low-lying basins within the stratigraphic sequence of coastal sectors along the southern coast (Algarve). Many of these deposits were firstly studied in detail in terms of spatial distribution, texture and micropalaeontological composition. One aspect that was noticed was the uniqueness of the CE 1755 event in the top of the Holocene sequence. The CE 1755 tsunami is well-known for its consequences all over the Atlantic basin however its epicenter is yet to be established with certainty. In that sense, over the last decade, a multitude of analysis and new sites were studied (Salgados, Alcantarilha, Furnas, Barranco, Almargem) and contributed to shed new light on the CE 1755 and on other extreme events that impinged the Portuguese coastal fringe. For example, boulder analysis and the erosional signature in dune fields were used to model wave flow characteristics (run-up, flow velocity and flow depth). On the other hand, grain-size data and heavy mineral composition established a robust source-to-sink relationship between the CE 1755 tsunami deposits and dune sediments. Similarly, microtextural analysis corroborated these findings reaching similar conclusions. The application of geochemistry and high-resolution micropaleontological analysis brought new insights in terms of inundation extent and in the establishment of inundation phases. All these analyses contributed to a better understanding of the CE 1755 tsunami dynamic and its onshore sedimentological imprint. Very recently, state-of-art hydrodynamic and morphodynamic modelling exercises have been conducted using this unique geological database to be validated. They contribute to exclude potential generation zones and to narrow down the search for the CE 1755 epicenter.

Another very innovative aspect is the recent study of the shelf area that is providing a ground-breaking opportunity to couple onshore and offshore palaeotsunami data and make inferences about the relevance of the backwash process on the depositional imprint.

This work will summarize the present state-of-knowledge on the Portuguese tsunami geological record, a unique tsunami geoscience case-study in Europe.

Authors acknowledge the financial support of FCT through projects UIDB/50019/2020–IDL and OnOff –

PTDC/CTAGEO/28941/2017.

How to cite: Costa, P., Bosnic, I., Feist, L., Dourado, F., Nobre Silva, A., Freitas, M. C., Reicherter, K., and Andrade, C.: Using Portuguese palaeotsunami deposits to reconstruct wave parameters and establish sediment sources, return periods and epicenters: a review on current knowledge, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10196, https://doi.org/10.5194/egusphere-egu2020-10196, 2020.

Japan, more precisely, the eastern coastal areas of Honshu, are one of the most affected areas of tsunamis in the world. Major events within the last century were three Sanriki-oki tsunamis (1896, 1933, 1968), and the most recent 2011 Tohoku-oki tsunami, triggered by the 9.1 M_W Tohoku-oki earthquake, which caused massive damage along the coastlines.

The 2011 Tohoku-oki tsunami overtopped the coastal defense walls with waves of 6-10 m height along the shores of the Aomori Prefecture in Northern Japan. The inundation reached up to 550 m inland, however, sandy tsunami deposits are limited to 250 – 350 m of the total inundation distance. At the field site of Misawa Harbor the well-preserved identifiable tsunami remains show up to 18 cm thick sand layers with sedimentary features, such as fining upward sequences, mud caps and rip-up clasts. The sandy deposits were enclosed in the soil of the coastal protection forest. Along with the sedimentary record of the tsunami, the use of organic geochemical indicators can provide a better understanding of the extend and processes, such as the deposition of tsunami layers and the backwash, of the inundation by the 2011 Tohoku-oki tsunami. The devastating damages caused by the interaction of tsunami and earthquake released pollutants associated as biological and anthropogenic markers. These released pollutants give the tsunami deposit an unique geochemical signature, that is distinguishable from the background sedimentation. Organic-geochemical results reveal a strong increase of anthropogenic (polycyclic aromatic hydrocarbons, pesticides and chlorinated compounds) and a variation of biological markers (i.e. n-alkanes, fatty acids) in the 2011 tsunami deposit close to the fishery port. During the analysis of the samples, another variation of biomarker and anthropogenic marker were identified right below the soil layer of the current forest. This layer is as well distinguishable from the paleo-dune that marks the lowest sedimentological unit at the field site. This differentiation shows the likely impact of a historical Sanriki-oki tsunami (1896, 1933 or 1968). These organic geochemical results in combination with local eyewitness reports of the tsunamis and lead to the assumption that the sedimentary archive of the Aomori coastline contains and preserved at two or more tsunami events of the last century.

The inclusion of organic geochemical markers to expand the characterizing and identifying proxies used in tsunami research are important to get a better understanding of the processes and deposition during tsunamis. Furthermore, this method can detect tsunami deposits beyond the visible recognizability of sedimentological identification of tsunami deposits and therefore can serve as a blue-print for historical and paleo-tsunami studies, as most of them only rely on visible sand deposits as marker for inundation distances from the beach. The high-resolution geochemical application can gain more information than standard techniques, like the identification of the “invisible” tsunami layer exceeding the limits of sandy deposits or the deposition in similar sedimentary textures, capturing a broader picture of the event.

How to cite: Frenken, M., Bellanova, P., Nishimura, Y., Schwarzbauer, J., and Reicherter, K.: Organic geochemical analysis of multiple tsunami deposits of the last century at the Aomori coast (Northern Japan), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7824, https://doi.org/10.5194/egusphere-egu2020-7824, 2020.

The first physical field evidence for any dated tsunami event on the coast of Israel was discovered twenty years ago.  Since then, three campaigns of offshore core collections were completed with the aim of testing the validity of that interpretation, further completing the catalogue of known tsunami events, providing constraining data for models, determining associations with potential source tsunami-generating mechanisms, and assessing risk for purposes of emergency planning and coastal management.  Those follow-up coring campaigns provided many additional examples of anomalous sedimentary deposits that agreed with tsunami-derived interpretations and failed to fit criteria of other potential causes (e.g. floods, storms); reinforcing the theory that multiple tsunami events impacted that coastline and building a more complete record.  The interpretation of these offshore deposits has been improved by ongoing contributions from modern sedimentological studies following the set of recent megatsunamis.  Specifically, tsunami sediment characterization from modern tsunami studies has greatly improved the ability to recognize cryptic, anomalous deposits with higher confidence.  In addition, a small set of new land-based evidence has been identified, some of which match written historical records, and many that corroborate the offshore sedimentary record. In this presentation, a summary of these finds and the latest, most updated catalogue of events based on physical sedimentary deposits will be presented highlighting knowledge gained regarding variations in the efficacy of various proxies in the tsunami ‘tool box’ with relationship with this particular stretch of coastline.

How to cite: Goodman Tchernov, B.: Recent Advances in the Identification of Onshore and Offshore Tsunami Deposits from the Eastern Mediterranean Coastline of Israel, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13521, https://doi.org/10.5194/egusphere-egu2020-13521, 2020.

At the nearshore area, strong and energetic flow fields can be easily formed during the tsunami event and it is hence expected coastal morphology is significantly affected by complex tsunami-induced current. In this study, the morphological changes by tsunami impacts on the US west coasts were investigated by numerical modeling. Firstly, we introduced a developed numerical model for calculating morphological changes by the tsunami wave, which incorporates a set of sub-models; hydrodynamics, sediment transport and morphological evolution models. The fully nonlinear Boussinesq-type model was adopted in the hydrodynamics calculations aiming at the better recreation of nearshore current fields which easily develop into turbulent flows due to various types of sources (e.g., wave-breaking). Then, the benchmark tests of one-dimensional or two-dimensional sedimentation problems were performed for validation; dam-break flow over the movable bed, breaking solitary waves over a sloping beach, partially breached dam-break flow over the mobile bed, and dam-break flows over a movable bed with a sudden enlargement. Calculated results revealed good agreement with the experimental records when a reasonable parameter has been chosen for closure models. As a real-scale application of the model, the 2011 Tohoku-Oki tsunami event was attempted, which subsequently presented a good prediction of tsunami-generated scouring and deposition in harbors. It was also confirmed that strong currents were successfully generated through the model, causing severe depth changes through the sedimentation process. To provide a rough guide for prospective users, we also performed several types of sensitivity tests on many parameters involved in the model

How to cite: Son, S., Jung, T., Kim, D.-H., and Yoon, H.-D.: Modeling morphological changes by tsunami Induced currents, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2839, https://doi.org/10.5194/egusphere-egu2020-2839, 2020.

Studies on recent on the deposits of recent tsunami and tropical cyclone events have provided the research community with new insights on the utility of their deposits. In addition, they also provide for the evaluation of some criticisms and knowledge gaps for future studies. There remain no globally applicable sedimentological criteria for differentiating between tsunami and storms deposits in either washover sandsheets or boulder deposits. What has been compiled for the many deposits attributed to tsunamis and storms is a suite of geomorphological or sedimentary features or commonalities, often referred to as signatures. All deposits regardless of type must be considered in terms of the local setting, and be carefully analysed for spatial relationships. Geomorphological characteristics and sedimentary features must also be considered in the context of the local environment. When considered alone many of the reported signatures for storms and tsunamis are equivocal. In fact, many of the signatures from the literature for tsunami or storm deposition, including the presence of marine microfauna or increases in particular elemental concentrations merely indicate the marine source of the material. Hence, storm surges, sea level change or co-seismic subsidence may show similar sedimentological characteristics. Efforts to differentiating between tsunami and storm deposits have stagnated and new approaches are needed. Addressing this need I will discuss my views on where the coastal geohazard community can go from here.

How to cite: Switzer, A. D.: The study of storm and tsunami deposits in the geological record: Are we going in circles? , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16785, https://doi.org/10.5194/egusphere-egu2020-16785, 2020.

Can we distinguish tsunami and storm deposits based on their microbial composition?

Wenshu Yap^1,2,3, Adam D. Switzer ^1,2, Chris Gouramanis⁴, Dale Dominey-Howes⁵, Maurizio Labbate⁶, Federico M. Lauro^1,3

¹ Asian School of the Environment, Nanyang Technological University, 50 Nanyang Drive, Singapore 639798

² Earth Observatory of Singapore, Nanyang Technological University, 50 Nanyang Drive, Singapore 639798

³ Singapore Centre for Environmental Life Sciences Engineering, Nanyang Technological University, 60 Nanyang Drive, Singapore 639798

⁴ Department of Geography, National University of Singapore, Kent Ridge, Singapore 117570

⁵ Asia-Pacific Natural Hazards and Disaster Risk Research Group, School of Geosciences, University of Sydney, NSW 2006, Australia

⁶ School of Life Sciences, University of Technology Sydney, NSW 2007, Australia

One of the challenges in the study of coastal hazard is to reliably distinguish between storm and tsunami deposited sediments. This limitation compromises the quality and accuracy of reconstructing historical coastal flooding records, and is thus an issue to a variety of policy makers and stakeholders interested in assessing the risk and vulnerability of coastal communities. Here we describe a microbial community signature based on amplicon sequencing of DNA extracted from environmental samples collected from two different locations i.e. Cuddalore, India and Phra Thong Island, Thailand. Both locations were impacted by the 2004 Indian Ocean Tsunami and a subsequent storm event. Our results show that the microbial community in the tsunami deposits are significantly different from that found in the storm deposits as well as soil and terrestrial sediments (PERMANOVA, p-value <0.01) in both locations. The microbial community differences between the tsunami deposits and storm deposits are not statistically correlated with chemical data such as total Nitrogen, total Carbon and total Sulfur, implying that our microbial signature is insensitive to environmental and geochemical variability. Integrating molecular techniques to investigate geological records is powerful and statistically robust in discriminating between modern tsunami and storm deposits.

How to cite: Yap, W., Adam, S., Chris, G., Dale, D.-H., Maurizio, L., and Federico, L.: Can we distinguish tsunami and storm deposits based on their microbial composition?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22090, https://doi.org/10.5194/egusphere-egu2020-22090, 2020.

Benthic foraminiferal studies were hardly comparable for several decades because of the absence of standardised size criteria. Actually, sample wash and foraminifera investigations in different studies addressed >63µm, >125µm, >150µm or even >250µm fractions. The turning point arrived with Schröder et al. (1987) and Sen Gupta et al. (1987). Both reported significant loss in the foraminifera and species abundances in the >125µm fraction, when compared with the >63µm. Dominant species in oceanic environment became non-significant or disappear, and the larger sieves record became obviously less informative. Schönfeld et al. (2012) consider that >125µm is adequate for ecological monitoring but point that, in some environments, to prevent losing smaller species and juveniles it is required to use the >63µm fraction. Recently, a worrying trend argues that solely the >150μm residue should be investigated to save time, even if it results on assemblages bias. Such trend represents an unacceptable step back. In fact 1) the analysis of coarser fractions reduces representativity of small, but relevant, adult species, effectively biasing both the associations and interpretations, 2) up to 50% (in cases 99%) of foraminiferal fauna may be lost, 3) this constrains comparison with published research and jeopardizes future work and 4) the contribution of juveniles (regardless of their identification) for sedimentary dynamic interpretations is lost. This is clearly the case of foraminiferal studies on tsunami deposits, where small species and juveniles often represent an important proxy to understand tsunami flow dynamics. For instance, in the Algarve 1755AD tsunami deposits juveniles represent up to 22% of the assemblage (e.g. Quintela et al., 2016).

Furthermore, >150µm fraction does not correspond to any Wentworth’s grain-size classes, precluding correlation between foraminifera and sediment textural features in tsunami deposits analysis (e.g., Hawkes et al., 2007;Mamo et al., 2009; Pilarczyk et al., 2019). Consequently it must be assumed that foraminiferal research is a time consuming task, and that “Yes, size matters!” thus small foraminifera cannot be disregarded and fraction >63µm should be mandatory in multiproxy analyses.

Authors acknowledge the financial support of FCT through projects OnOff – PTDC/CTAGEO/28941/2017 and  UIDB/50019/2020–IDL.

Hawkes, AD et al. (2007). Sediments deposited by the 2004 Indian Ocean Tsunami along the Malaysia-Thailand Peninsula. Marine Geology 242, 169-190.

Mamo, B et al (2009). Tsunami sediments and their foraminiferal assemblages. Earth-Science Reviews 96, 263-278.

Pilarczyk, J et al. (2019).Constraining sediment provenance for tsunami deposits using distributions of grain size and foraminifera from the Kujukuri coastline and shelf, Japan. Sedimentology doi: 10.1111/sed.12591

Quintela, M et al. (2016). The AD 1755 tsunami deposits onshore and offshore of Algarve (south Portugal): Sediment transport interpretations based on the study of Foraminifera assemblages. Quaternary International, 408: 123-138.

Schönfeld, J and FOBIMO group (2012). The FOBIMO (FOraminiferal BIo-MOnitoring) initiative—Towards a standardized protocol for soft-bottom benthic foraminiferal monitoring studies. Marine Micropaeontology 94-95, 1-13.

Schröder, CJ et al. (1987). Can smaller benthic foraminifera be ignored in Paleoenvironmental analysis? Journal of Foraminiferal Research 17, 101-105.

Sen Gupta, BK et al. (1987). Relevance of specimen size in distribution studies of deep-sea benthic foraminifera. Palaios 2, 332-338.

How to cite: Fatela, F., Costa, P., Silva, A., and Andrade, C.: SIZE MATTERS! (Or the crucial importance of small foraminifera in interpreting tsunami sediments), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5843, https://doi.org/10.5194/egusphere-egu2020-5843, 2020.

On the 1^st November AD 1755, the tsunami, triggered by the 8.5 to 9 M_W 1755 Lisbon earthquake, caused major inundations with sediment transport along the coastline of the Gulf of Cadiz. The study area, Conil de la Frontera (El Palmar de Vejer), located at the Gulf of Cadiz in southwestern Spain, was severely stuck by the AD 1755 Lisbon tsunami. Witness of the destruction and power of the tsunami inundation are the walls of Torre de Castilnovo, close to the study area, which got heavily destroyed. El Palmar de Vejer was chosen as a study area due to the topographical setting, characterized by the flat alluvial flood plain. With these peculiarities, the area presents good preconditions as a sedimentological archive for potential deposits of the AD 1755 tsunami.

First, geophysical methods were used to identify potential sandy layers attributed to the AD 1755 tsunami. Ground-penetrating radar (270 MHz antenna) was used to systematically scan the ground to a depth of ca. 3 m. The evaluation of these radargrams were taken into account for the selection of GeoSlicer drilling locations. Based on the samples obtained, granulometric analyses were carried out (1) to identify the potential sandy tsunami deposit; (2) to analyze the different sedimentological depositional environments before, during and after the tsunami; (3) to detect tsunami sublayers deriving from different waves within the wave-train of  the AD 1755 Lisbon tsunami, since 3 waves were reported.

Furthermore, both inorganic and organic geochemical investigations were performed on the samples. With the help of inorganic geochemical analysis of major elements (Si, Sr, Ti, Ca, N, S) as well as elemental ratios can identify a distinction between marine and terrestrial depositional environments and accumulate more information about the deposit facies. By the use of organic geochemistry for the analysis of biomarker, several different natural compounds were detected (e.g., n-alkanes, n-aldehydes). Biomarker results suggest a distinct differentiation between the AD 1755 tsunami deposit and the surrounding background sediment layers above and below. The tsunami deposits contrasts to the post and pre-tsunami layers by different concentrations of biomarkers and deviant occurrence of specific compounds. The n-alkanes are manifesting the difference of marine and terrestrial sources of the different layers. Results of this study analyzing the Iberian sedimentary archives at Conil de la Frontera present strong evidence that a multi-proxy approach with the inclusion of geochemical applications can confidently detect tsunami deposits, distinguish them from surrounding background sediments and subsequently characterize the internal structure and composition of the tsunami deposit.

How to cite: Cämmerer, C., Frenken, M., Bellanova, P., Chaumet, M., Schwarzbauer, J., and Reicherter, K.: AD 1755 Lisbon tsunami deposits – geophysical, sedimentological and organic geochemical analysis (Conil de la Frontera, Spain), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7988, https://doi.org/10.5194/egusphere-egu2020-7988, 2020.

The southwest of the Iberian peninsula is, due to its border position between Africa and Europe, a key territory of major geoarchaeological interest, as well as a reservoir of biodiversity and a wildlife refuge area during the Holocene. Bioclimatic conditions have been significantly unstable during this period in the Western Mediterranean. Therefore, further studies are still required to understand how abrupt climate changes such as the 8.2 and 4.2 ka cal BP events impacted societies and environment.

In November 2018 the RV Meteor cruise M-152 retrieved 19 vibracores and 4 gravity cores along the Algarve coast after mapping the bathymetry. One of these cores, GeoB23519-01, was taken 65 m below present sea level and recovered 365 cm of sediment. Four potential event layers were identified over the last 11 ka cal BP and, at least two of them, are related to tsunami deposits (ca. 4370 cal BP and AD 1755).

This sedimentary archive was analysed in a multi-proxy approach, including palynological and micropalaeontological analyses, which allow characterizing palaeoenvironmental changes along the core. However, considering the characteristics of these deposits, we raise questions about how complex this palynological record is and how it mirrors some short-term events, climate dynamics, and cultural disruptions.

How to cite: Val-Peón, C., Eichner, D., López-Sáez, J. A., Reicherter, K., Feist, L., Costa, P. J. M., Bellanova, P., Santisteban, J. I., Bosnic, I., Schwarzbauer, J., Frenken, M., Vött, A., Brückner, H., Schüttrumpf, H., Andrade, C., Duarte, J. F., and Kuhlmann, J.: How to interpret Holocene palaeoenvironmental and cultural changes in SW Iberia based on the palynological record from the GeoB23519-01 core (RV METEOR cruise M152), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13902, https://doi.org/10.5194/egusphere-egu2020-13902, 2020.

The importance of tsunami hazard assessment is only possible if a complete dataset of events is available, allowing the determination of the recurrence intervals of the tsunamis adapted to local and regional conditions. One possible way to know these intervals is to study the offshore sedimentary record, looking for sediment remobilised and transported by the incoming tsunami waves and generated backwash currents. Even if these deposits are not of easy access (and not so well studied), the tsunami depositional signature has potential to be better preserved than those located onshore.

A multidisciplinary approach was performed to detect the sedimentary imprints left by the 1755 CE Lisbon tsunami event in three cores located in southern Portuguese continental shelf at water depths between 57 and 91 m. Age models based on ¹⁴C and ²¹⁰Pb_xs data allowed a probable correspondence with the 1755 CE Lisbon tsunami.

The present study was based in high-resolution analyses using several methodologies such as sand composition, grain size, inorganic geochemistry and microtextural features on quartz grain surfaces. The results yielded evidences for a tsunamigenic origin although no remarkable terrigenous signal is present. Spatial depositional differences of tsunami sediments were detected in the study area by differences in grain size, sand composition and simulated horizontal surface velocities. Also, the heterogeneous and mixing character of the 1755 CE Lisbon offshore tsunami deposits indicate more complex sedimentary conditions compared to the background sedimentation.

This study shows that in fact the sediment layers corresponding to a tsunami event can be preserved in mid to outer continental shelf environments (other extreme events such as storms were excluded trough hydrodynamic calculations), but its identification and characterization can be done only with a good assemblage of different proxies.

This is a contribution of ASTARTE project (FP7-Grant agreement no: 603839) and CIMA project (UID/MAR/00350/2013).

How to cite: Kümmerer, V., Drago, T., Veiga Pires, C., Silva, P., Lopes, A., Magalhães, V., Roque, C., Rodrigues, A. I., Terrinha, P., Mena, A., Francés, G., Kopf, A., Völker, D., Salgueiro, E., Alberto, A., Lopes, C., Costa, P., and Baptista, M. A.: Offshore 1755 CE Lisbon Tsunami Deposit in the Southern Portuguese Continental Shelf, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20706, https://doi.org/10.5194/egusphere-egu2020-20706, 2020.

In AD 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 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.

Along the Algarve coast, prominent AD 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 m. The cores were analysed in a multiproxy approach (granulometry, magnetic susceptibility, P-wave velocities, organic and inorganic geochemistry, micropalaeontology). Deposits of the AD 1755 Lisbon tsunami were identified in most of the cores as a thin layer at ca. 20 cm depth.

More surprisingly, a second event deposit dating to ca. 3700 years cal. BP was detected at core depths of 122 to 155 cm. It is even traceable in the sub-bottom profiles and consists of a distinctive ca. 30 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_a division of the Bouma sequence or the S₁, S₂ and S₃ 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.

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.

How to cite: Feist, L., Reicherter, K., Costa, P. J. M., Bellanova, P., Santisteban, J. I., Bosnic, I., Val-Peón, C., Schwarzbauer, J., Frenken, M., Vött, A., Brückner, H., Schüttrumpf, H., Andrade, C., Duarte, J. F., Kuhlmann, J., and M152 scientific team, T.: The continental shelf as an offshore archive for tsunami deposits – an example from southwest Iberia (RV METEOR cruise M152), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8504, https://doi.org/10.5194/egusphere-egu2020-8504, 2020.

Preserved on land coastal tsunami deposits onshore have rarely been reported for the coastline of Israel. According to offshore sedimentological records, a tsunami struck the coast of early Islamic Caesarea Maritima, likely coinciding with a major earthquake in 749 AD. Anomalous sand layers from the same time period were reported by archaeologists in structures near the shore, but they were recorded with varied interpretations (construction fill, dune development, general abandonment). Unfortunately, no sediments were collected nor analyzed from those excavations. Recently, an area with this same deposit was freshly excavated. This allowed it to be studied to determine its taphonomic history. The deposit is comprised of a thick, well-sorted sand layer with semi-articulated sequences of building stones followed by independent matrix-supported building stones, the entire deposit sandwiched between an early-eighth century abandonment layer and a late-eighth century floor. Two sediment cores from the deposit, as well as reference samples representative of other depositional environments, have been analyzed for grain size distribution, foraminiferal abundance, diversity, taphonomic characterization, relative age by portable luminescence (POSL), and loss on ignition. In tandem, reference samples from modern beach, dunes, an eighth century archaeological construction fill, and shallow marine sands were analyzed as reference samples for comparison. The combination of results indicates that the sandy deposit formed during a high-energy event, and does not resemble other known types of sand deposits in the area, including those suggested as possible interpretations by the excavators. The results of this study will contribute to the understanding of tsunami deposits preserved on land in Caesarea Maritima, provide geographical constraints to enhance coastal inundation models and hazard/risk area maps, and more broadly contribute to the understanding of tsunami sedimentological studies in geoarchaeological contexts. 

How to cite: Everhardt, C., 'Ad, U., Barkai, O., Jaijel, R., Robins, L., Roskin, J., and Goodman-Tchernov, B.: Tsunami-derived sediments identified in the destruction sequence of an 8th century warehouse in Caesarea Maritima, Israel, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11412, https://doi.org/10.5194/egusphere-egu2020-11412, 2020.

Catastrophic coastal flooding is one of the main forcing agents of short-term coastal system changes and represents a major threat to human activities concentrated along the coasts worldwide, particularly in the light of ongoing climate change. In order to better understand the frequency and character of catastrophic marine inundation events in the past as well as to predict future trends the knowledge on the long-time records of Holocene coastal flooding chronologies is necessary.

The southern coast of the Baltic Sea is an important study area because it is exposed to both, (north) westerly and (north) easterly storms and corresponding seiche effects. Moreover, the negligible tidal forcing does not bias the elevated water table of marine water surge events, so the true coastal flooding signal is preserved in the sedimentary record (Hippensteel, 2010). Furthermore, as demonstrated in a recent study by Piotrowski et al. (2017) in the area of Polish coast the low lying marsh areas behind coastal dunes or at river mouths are promising sedimentary environments to provide with record of catastrophic coastal flooding.

The poster reviews the most up-to-date state of palaeo-tempestological research within the southern Baltic Sea coast summing up the newest findings of the CatFlood project launched in March 2019. The overview of topographical and geomorphological characteristics of field locations, which are most prone to marine coastal flooding and preservation of sedimentological evidence for these catastrophic events will be given based on the pilot study within 16 field locations. The study sites are scattered along whole Polish Baltic Sea coast. Furthermore, in depth observations of features of deposits associated with marine inundation events is provided based on the detailed analysis of sediments from four selected key field locations. The event- layers characteristics are reconstructed by standard techniques such as grain size, shape and texture, heavy mineral composition, mineral versus organic matter ratio analyses. Above that the analysis of internal structure of flooding deposits in microscale is described from thin sections. The composite chronologies and the high resolution age control based on both ¹⁴C dating and ²¹⁰Pb/¹³⁷Cs provides with insights into the chronology of these events. A new approach is the application of seda-DNA analysis in deciphering the marine character of event deposits.

References:

Hippensteel,  S.P.,  2010.  Paleotempestology  and  the  pursuit  of  the  perfect  paleostorm  proxy.  GSA Today 20, 52-53.

Piotrowski,  A.,  Szczuciński,  W.,  Sydor,  P.,  Kotrys,  B.,  Rzodkiewicz,  M.,  Krzymińska,  J.,  2017. Sedimentary  evidence  of  extreme  storm  surge or tsunami  events  in  the  southern  Baltic  Sea (Rogowo area, NW Poland). Geological Quarterly 61, 973-986.

The research project CatFlood is funded by National Science Centre, Poland,

OPUS grant nr: 2018/29/B/ST10/00042

How to cite: Leszczyńska, K., Moskalewicz, D., Stattegger, K., and Szczuciński, W.: Catastrophic coastal flooding events along the southern Baltic Sea coast during the Late Holocene., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13147, https://doi.org/10.5194/egusphere-egu2020-13147, 2020.

Onshore tsunami deposits provide crucial information on tsunami recurrence patterns in flood-prone areas. Their composition is mainly a function of the site-specific coastal sediment system, bathymetry, and onshore topography and flow conditions. Microfossils (e.g. foraminifera, ostracods, diatoms) are often utilised to recognize tsunami deposits and differentiate them from other deposits. Foraminifera found within tsunami deposits mostly comprise allochthonous associations dominated by benthic intertidal to inner shelf taxa. Specimens may also originate from outer shelf to bathyal depths; even planktonic forms may occur. Furthermore, changes in test numbers, taphonomy, size or adult/juvenile ratios compared to background sedimentation are common. However, post-depositional degradation (e.g. dissolution) of carbonate tests often prevents identification, thereby reducing their value as a proxy.

The project “GEN-EX - Metagenomics of Extreme Wave Events” aims at developing high-throughput, metagenomic sequencing techniques to identify foraminifera assemblages and to unravel their cryptic diversities in onshore extreme wave deposits from their environmental DNA (eDNA) signature. The project has sampled tsunami deposits from coastal peat sections at three sites on the Shetland Islands, UK, dated to approximately 1.5, 5.5 and 8 ka BP, respectively. Tsunami deposits were identified by utilising integrative high-resolution grain-size analysis, CT scanning, multi-sensor core logging and geochemical analyses. When applying classical micropalaeontological techniques, no foraminiferal tests were found in any of the tsunami deposits analysed to date, whilst inter- to subtidal offshore source deposits show moderate to high foraminiferal concentrations, indicating possible severe post-depositional dissolution of foraminifera in the onshore tsunami deposits, which are bracketed in between massive dystrophic peats.

Several different extraction methods, polymerase chain reaction (PCR) protocols (to amplify target regions of the foraminifera DNA) and primers were tested. So far, the S14 F3 and S14 F1 primers were able to amplify the DNA of specific foraminiferal taxa from modern offshore samples, but this approach was less successful for the palaeo-samples. Current tests are focusing on targeting the amplification of another region of the foraminiferal DNA (V9), with the best available protist specific universal DNA primers at present. Possible reasons for the challenges in amplifying foraminifera DNA in the palaeotsunami samples may be due to the high age of the deposits and time-associated DNA degradation; transportation and storage of samples at ~-20 °C may also be key. However, it is possible that the foraminifera DNA is altogether absent from the sediment collected, even though this is considered unlikely given the number of tests recorded and identified in the potential subtidal source sediments. Thus, at present, a “shotgun sequencing” approach is being applied to these samples to obtain the eDNA signal in its entirety from the remains of all taxa within the sediment.

Finally, our tests so far have further revealed that the extraction method and DNA amplification protocols must be modified individually for each of the different sample types, i.e. modern offshore, modern intertidal and palaeotsunami samples, posing an added challenge to this metagenomics research. A comprehensive summary of all recommendations will be made available in the near future.

How to cite: Engel, M., Patel, T., Dawson, S., Pint, A., Schön, I., and Heyvaert, V. M. A.: Metagenomics of tsunami deposits: developments, challenges and recommendations from a case study on the Shetland Islands (UK), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18238, https://doi.org/10.5194/egusphere-egu2020-18238, 2020.

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 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).

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.

How to cite: Schwarzbauer, J., Bellanova, P., Frenken, M., Jaffe, B., Szczuciński, W., and Reicherter, K.: Anthropogenic pollutants and biomarkers for the identification of 2011 Tohoku-oki tsunami deposits (Japan), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8218, https://doi.org/10.5194/egusphere-egu2020-8218, 2020.

Heavy minerals in tsunami and storm deposits have been used to establish sediment sources and to infer the inundation and backwash phases (Morton et al., 2007). The abundance of these minerals is dependent on the hydrodynamic conditions that existed during transport and depositional stages. Overall, heavy mineral analysis allowed interpretations on sediment dynamics. Heavy mineral studies on tsunami deposits allowed the establishment of source-to-sink relationships thus, contributed to establish transport paths and inundation routes (Jagodzinski et al., 2012; Putra et al., 2013; Costa et al., 2015; Cascalho et al., 2016).

After the Tohoku-oki tsunami event, GeoSlicer were excavated and tsunami imprints were retrieved from the slices in Misawa coastal area (Japan). Heavy minerals from thirty-six samples were analyzed. Heavy minerals in the sediment fraction of 0.125-0.500 mm were separated by centrifugation in sodium polytungstate (2.90 kg/m³) and recovered by partial freezing with liquid nitrogen. An average of about 220 transparent heavy-mineral grains per sample were identified and counted under a petrographic microscope. Heavy minerals not mounted on glass slides were subjected to the ferromagnetic separation using a Frantz Isodynamic Magnetic apparatus to estimate the weight of magnetite in each sample.

Heavy-mineral weight in total sediment fraction presented a mean value of 31%, ranging between 18 and 59%. The magnetite weight percentage present in the heavy-mineral fraction has a mean of 26% ranging between 14 and 43%.

Considering the mean frequency of the transparent heavy minerals it was identified the presence of orthopyroxenes (67%), followed by clinopyroxenes (30%).

These results indicate that the main original source of heavy minerals are basic volcanic rocks. The wide ranges of variation of the total heavy mineral fraction and the magnetite present in that fraction provides useful information about the flow competence of the tsunami waves. The samples that reveal higher concentration in total heavy minerals tend to be richer in magnetite. These results could be used to pinpoint water flow conditions (velocity thresholds) promoting grain sorting leading to the formation of layers enriched in heavy minerals. Confirming previous cases, heavy mineral analysis in Misawa tsunami deposit seems to provide useful insights into tsunami-derived sediment dynamic. 

Cascalho, J., Costa, P., Dawson, S., Milne, F. and Rocha, A. 2016. Heavy mineral assemblages of the Storegga tsunami deposit. Sedimentary geology, 334, 21-33.     

Costa, P.J., Andrade, C., Cascalho, J., Dawson, A.G., Freitas, M.C., Paris, R. and Dawson, S., 2015. Onshore tsunami sediment transport mechanisms inferred from heavy mineral assemblages. The Holocene, 25(5), pp.795-809.

Jagodziński, R., Sternal, B., Szczuciński, W., Chagué-Goff, C. and Sugawara, D., 2012. Heavy minerals in the 2011 Tohoku-oki tsunami deposits—insights into sediment sources and hydrodynamics. Sedimentary Geology, 282, pp.57-64.

Morton, R.A., Gelfenbaum, G. and Jaffe, B.E., 2007. Physical criteria for distinguishing sandy tsunami and storm deposits using modern examples. Sedimentary Geology, 200(3-4), pp.184-207.

Putra, P.S., Nishimura, Y., Nakamura, Y. and Yulianto, E., 2013. Sources and transportation modes of the 2011 Tohoku-Oki tsunami deposits on the central east Japan coast. Sedimentary Geology, 294, pp.282-293.

The author would like to acknowledge the financial support FCT through project UIDB/50019/2020 – IDL and by FCT OnOff project PTDC/CTAGEO/28941/2017.

How to cite: Cascalho, J., Abrantes, A., Costa, P., Bellanova, P., Frenken, M., and Reicherter, K.: Heavy minerals analysis on tsunami deposits from Misawa (Japan) , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18726, https://doi.org/10.5194/egusphere-egu2020-18726, 2020.

Coastal boulder deposits are records of unusually powerful wave action events associated with either storms or tsunamis. Our 2016 paleotsunami survey of the southeastern Java coast led to the discovery of five coastal boulder fields near Pacitan, Indonesia, possibly dating to the mid-to-late 19th century or prior, and two similar fields at Pantai Papuma and Pantai Pasir Putih that were tsunami-emplaced during the 1994 7.9 Mw event in East Java. Both multiyear photogrammetry and hydrodynamic wave height reconstructions of the accumulations near Pacitan suggest the boulders were likely tsunami rather than storm-wave emplaced. We evaluate the boulders as an inverse problem, using reconstructed wave heights and ComMIT tsunami modelling to suggest a minimum 8.4 Mw earthquake necessary to dislodge and emplace the largest boulders near Pacitan assuming they were all deposited during a single seismic event and that the rupture source was located along the Java Trench, some 200 km south of Pacitan.

How to cite: Meservy, W., Harris, R., Setiadi, G., and Hapsoro, S.: Coastal boulder fields and tsunami hazards of East Java, Indonesia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22118, https://doi.org/10.5194/egusphere-egu2020-22118, 2020.