Search

International audience

In ad 1362, a major storm surge drowned wide areas of cultivated medieval marshland along the north‐western coast of Germany and turned them into tidal flats. This study presents a new methodological approach for the reconstruction of changing coastal landscapes developed from a study site in the Wadden Sea of North Frisia. Initially, we deciphered long‐term as well as event‐related short‐term geomorphological changes, using a geoscientific standard approach of vibracoring, analyses of sedimentary, geochemical and microfaunal palaeoenvironmental parameters and radiocarbon dating. In a next step, Direct Push (DP)‐based Cone Penetration Testing (CPT) and the Hydraulic Profiling Tool (HPT) were applied at vibracore locations to obtain in situ high‐resolution stratigraphic data. In a last step, multivariate linear discriminant analysis (LDA) was successfully applied to efficiently identify different sedimentary facies (e.g., fossil marsh or tidal flat deposits) from the CPT and HPT test dataset, to map the facies' lateral distribution, also in comparison to reflection seismic measurements and test their potential to interpolate the borehole and CPT/HPT data. The training dataset acquired for the key site from coring and DP sensing finally allows an automated facies classification of CPT/HPT data obtained elsewhere within the study area. The new methodological approach allowed a detailed reconstruction of the local coastal landscape development in the interplay of natural marsh formation, medieval land reclamation and storm surge‐related land losses., Presenting a new approach of automated facies identification based on palaeoenvironmental parameter (PEP) analyses of vibracores, Direct Push‐based Cone Penetration Testing (CPT) and the Hydraulic Profiling Tool (HPT) sensing data, linear discriminant analysis (LDA) and seismic measurements, gradual as well as extreme landscape changes associated with major storm surges in ad 1362 and ad 1634 are reconstructed for a study area in the Wadden Sea of North Frisia (Germany). image, Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659, Research Foundation http://dx.doi.org/10.13039/100005930

Geophysical and geoarchaeological investigations were carried out in the Wadden Sea of North Frisia (Schleswig-Holstein, Germany) to elucidate major environmental changes that considerably altered the coastal landscape since medieval times. Between the 12 th and 14 th cent. AD, the present-day tidal flats around the marsh island Hallig Sudfall belonged to the historical Edomsharde district and its main settlement Rungholt . For North Frisia, it is well known that during medieval and early modern times, extreme storm surges caused major land losses associated with a massive landward shift of the coastline. Today, cultural traces like remains of dikes, drainage ditches, terps or even plough marks are still visible in the Wadden Sea and provide evidence of the once cultivated marshland. Based on a multi-proxy analysis of sediment cores retrieved from the tidal flat zone around Hallig Sudfall and from the Hallig itself, we identified a late medieval paleosol associated with the formerly cultivated marshland most probably belonging to the Edomsharde and local trade centre of Rungholt. Around Hallig Sudfall, remains of medieval marsh deposits were found partly eroded and covered by a coarse-grained high-energy deposit including abundant shell debris and artefacts. Based on sedimentological, micropaleontological, geochemical and geochronological data, we conclude that these deposits are associated with the 1 st Grote Mandrenke (or St. Marcellus’ flood ), an extreme storm surge event in 1362 AD. Our results, for the first time, provide geological evidence of this 1362 AD storm surge for the Wadden Sea of North Frisia. Moreover, marshland on Hallig Sudfall dating to the 17 th -18 th cent. AD was found covered by a thick layer of storm surge sand and shell debris which seems to be associated with one of the major storm event that hit the German North Sea coast in modern times, e.g. the 2 nd Grote Mandrenke (or Burchardi flood ) in 1634 AD or the Christmas flood in 1717 AD.

International audience

The Late Bronze Age (LBA) tsunami and the A.D. 365 tsunami are supposed to have affected the northern coasts of Crete. However, near-coast sedimentary archives have been rarely investigated in this area, and sedimentary archives including palaeotsunami fingerprints are still unknown. The main objective of our research was to search for appropriate tsunami sediment traps in order to gain detailed insights into the Holocene palaeotsunami history of northern Crete. We found an excellent fine sediment archive near Pirgos, located to the west of Rethymnon. Based on a multi-electrode geoelectrical survey and an 11-m-deep sediment core, we analysed the event-geochronostratigraphical record by means of sedimentological, geochemical, geochronological, geomorphological, and microfossil investigations. The Pirgos record revealed a thick unit of homogeneous mud of a lagoonal environment starting ~6000 years ago. The lagoon was affected by five high-energy events, leaving layers of allochthonous sand. Microfossil analyses of these layers revealed a mixed foraminiferal assemblage including species from brackish habitats but also displaced and transported species from open marine and deep-water environments. Considering sedimentary characteristics, the local wave climate of the Cretan Sea, and the overall geomorphological setting, we interpret these layers as related to extreme wave events (EWE). Based on a local radiocarbon age-depth-model, we identified one EWE layer as a reliable candidate for the LBA Santorini tsunami. Another EWE layer is most probably associated with the A.D. 365 tsunami. This EWE ended abruptly the lagoonal conditions at Pirgos because of to the 1.64 m coseismic uplift at the site. The Pirgos lagoon existed between the first half of the 6th mill. B.C. and (at least) the end of the 2nd mill. B.C. We found that the area around Pirgos has continuously subsided over 3000 or so years, reflecting constant tectonogeomorphological conditions dominated by the nearby subduction zone between the Aegean and African plates.

In antiquity, the harbour-city of Corcyra (modern: Corfu) was a prevailing naval power in the Mediterranean and had several harbours to host a considerable fleet. Today, these harbours are totally or partly silted and concealed under modern urban infrastructure. Comprehensive geoarchaeological studies were conducted on the northeastern fringe of the Analipsis Peninsula where excavations have revealed the archaeological remains of a massive quay wall (Pierri and Arion sites). These remains are located east of known ancient harbour structures that belong to the Alkinoos Harbour. Our study aimed to reconstruct the palaeoenvironmental setting of the harbour facilities at the Pierri site, including the analysis of the local sedimentary record in order to detect and differentiate natural and man-made triggers that caused environmental shifts. At the Pierri site, we found geoarchaeological evidence for an ancient harbour basin related to the prominent quay wall. Associated harbour sediments indicate a protected harbour which was developed from an open shallow marine environment, most probably by the construction of breakwaters. Harbour deposits were dated using radiocarbon analyses and diagnostic ceramic fragments to the 4 th to 3 rd cent. BC. This is in good agreement with the age of the harbour installations as such archaeologically assigned to the Classical and Hellenistic period. The Pierri site was possibly in function as a harbour facility even before the 4th cent. BC. In any case, it was strongly hit by an earthquake and associated tsunami event during Classical to Hellenistic times. By this event, the harbour was uplifted and covered by event deposits so that it was not usable any more. It was subsequently buried by anthropogenic and colluvial sediments. Overall, the Pierri coastal archive allowed to identify three distinct tsunami landfall events, namely before 2483–2400 cal BC (event I), after 2483–2400 cal BC and before 370–214 cal BC (event II), and during Classical to Hellenistic times, most probably between the 4 th and 3 rd cent. BC (event III). Another tsunami event (event IV) potentially hit the site when it was dry land. Ages of tsunami events I–II and candidate tsunami IV are consistent with tsunamis known from the coasts of western Greece and southern Italy and where thus classified as supra-regional tele-events. Event III was identified as associated to a local earthquake and tsunami by which Corfu Island was uplifted and, at the same time, tilted with a vertical offset of 1.74 m from W to E.

The southwestern coast of Crete, one of the most seismically active regions in Europe, experienced co-seismic crust uplift by 9 m during the Ms = 8.3 mega-earthquake that struck the eastern Mediterranean world on 21 July AD 365. An associated tsunami event caused thousands of fatalities and destroyed many coastal settlements and infrastructure between the Levante in the east and the Adriatic Sea in the northwest. So far, coastal sedimentary archives in southwestern Crete including distinct palaeotsunami fingerprints are rarely investigated. Therefore, a multi-proxy study including sedimentological, geochemical, geochronological, and microfaunal methods was conducted in order to detect onshore coastal sedimentary archives that functioned as fine sediment traps and document palaeotsunami imprint. We found adequate archives at the Sougia and Palaiochora coastal plains that were used to reconstruct the palaeogeographical evolution and the palaeoseismological history of SW Crete during the late Holocene. Our studies revealed distinct geomorphological, sedimentological, geochemical, and microfaunal traces of high-energy impact from the marine side related to seismic events. At the Sougia coastal plain a sheet of fine sand with a neat microfossil and geochemical fingerprint was found sandwiched between underlying pre-tsunami muds and overlying post-tsunami colluvial silt. In the Palaiochora coastal plain, tsunami overflow of a flat Neogene bedrock platform led to the accumulation of sand-dominated deposits that were subsequently covered by colluvial material from the adjacent hillslopes. Based on radiocarbon and luminescence dating approaches, it is shown that the AD 365 tsunami event is the best-fit candidate for the tsunami-related sediments deposited at both, Sougia and Palaiochora. This study, for the first time, presents multi-proxy evidence of the AD 365 tsunami imprint on fine-sedimentary archives along the western and southwestern coast of Crete.