A review on onshore tsunami deposits along the Atlantic coasts (original) (raw)
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Minerals
Outer shelf sedimentary records are promising for determining the recurrence intervals of tsunamis. However, compared to onshore deposits, offshore deposits are more difficult to access, and so far, studies of outer shelf tsunami deposits are scarce. Here, an example of studying these deposits is presented to infer implications for tsunami-related signatures in similar environments and potentially contribute to pre-historic tsunami event detections. A multidisciplinary approach was performed to detect the sedimentary imprints left by the 1755 CE tsunami in two cores, located in the southern Portuguese continental shelf at water depths of 58 and 91 m. Age models based on 14C and 210Pbxs allowed a probable correspondence with the 1755 CE tsunami event. A multi-proxy approach, including sand composition, grain-size, inorganic geochemistry, magnetic susceptibility, and microtextural features on quartz grain surfaces, yielded evidence for a tsunami depositional signature, although only a...
Tsunami deposits in the geological record
Sedimentary Geology, 2007
A review is presented here of tsunami deposits in the geological record. It begins with a discussion of the relationships between the processes of tsunami generation and propagation and the sedimentary responses. This is followed by a consideration of the sedimentary processes associated with the passage of tsunami waves across coastlines. Attention is also given to the sedimentary processes associated with tsunami-triggered gravity backwash flows and comparisons are made with turbidity current action. We observe that despite sedimentary evidence for recent tsunamiites, geological research on ancient tsunamis has not identified stratigraphic units associated with onshore tsunami sedimentation. Equally, it is noted that nearly all published studies of sedimentary processes associated with modern tsunamis have not considered patterns of sediment transport and deposition in the offshore zone.
2nd tsunami field symposium, GI2 …, 2008
A compilation of historical testimonies of tsunami flooding of the Portuguese Algarve coast was combined with a geomorphological characterization of that coast to produce a data base on locations prone to inundation by such high energy events. Field work has been undertaken in the lowland areas identified by this methodology between Sagres and Lagos in order to characterize the correspondent geological evidences. Results indicate that some locations vulnerable to inundation failed to preserve any sedimentological trace of extreme marine inundation. However, the completeness of the data base on these events significantly increases when the historical record is added by geological information. The sedimentary signature of tsunami inundation of the studied coastal section is varied and it may have been severely damaged by the intense anthropogenic activities that characterize the Algarve coast.
The identification of palaeo-tsunami deposits–a major challenge in coastal sedimentary research
… und Auswirkungen im …, 2010
Extreme wave conditions associated with severe storms or tsunamis represent major hazards along coasts worldwide. For appropriate hazard assessment, reliable information on the magnitude and frequency of catastrophic events of the past is crucial. Especially in areas where historical accounts are fragmentary or cover only short periods, the onshore sedimentary record provides a promising key to reconstruct impacts of extraordinary waves. However, the differentiation between tsunami and storm surge deposits in onshore stratigraphies is extremely difficult, since most of their characteristics only indicate marine flooding. We discuss the most recent strategies to identify tsunami sand and mud deposits in coastal stratigraphies. In order to pre-evaluate the local hazard, (i) potential tsunami triggering mechanisms (local -regional -far-field), (ii) local and regional historical accounts (including historical documents/tsunami catalogues, interviews with contemporary witnesses, etc.) on the effects of tsunamis and severe storms, and (iii) extreme atmospheric conditions have to be analyzed. A holistic study of the sedimentary environments within the area of interest (especially source areas) is essential since it will determine the sedimentary record of any extreme wave event. Local reference deposits from either recent or historically well documented tsunami or severe storm surges guarantee the safest conclusions and should be favoured over a schematic application of global 'tsunami signature types'.
The sedimentary inventory of tsunamis along the southern Gulf of Cadiz (southwestern Spain)
Zeitschrift f&# 252; r …, 2010
Outcrop evidence and shallow percussion drilling in coastal areas proved sedimentary evidence for paleo-tsunamis along a 50 km long segment of the Atlantic coast of southern Spain. The coast between Barbate and Tarifa yielded several depositional environments to preserve tsunamigenic layers, both on top of rocky cliffs as well as in lagoons, marshlands and along sedimentary beaches. Also, we focused on bays with river inlets, which are most probably sheltered from direct tsunami wave action. In these bays, the Roman villages of Baelo Claudia and Mellaria are situated. We found no evidence for tsunamigenic sediments there. On the other side, the findings of an enigmatic, most probable tsunamite has been encountered upon the cliff along the Barbarte-Zahara de los Atunes beach in various heights above mean sea level. Because only one dark-colored fining-up layer with a paleocurrent direction towards the sea has been found directly resting on folded Betic substratum, we interpret this layer as tsunamigenic back wash sediments. The last major event that affected severely the coast of the Gulf of Cádiz was the 1755 Lisbon tsunami. Reportedly, wave heights reached > 10 m in the study area. So, it is likely that coastal changes and deposition of tsunamigenic sediments in this area occurred, being attributed to this 1755 event. However, also older sedimentary relicts of tsunamis have to be taken into account, because sedimentary cores yield evidence for multiple intercalations.
Sedimentary Geology, 2007
The occurrence of numerous, recent, large tsunami suggests that they are a common natural event, yet tsunami deposits in the geological record are rare. This apparent anomaly may be due to a real infrequency of events and/or poor preservation potential but alternatively may be due to misidentification. Robust criteria for the discrimination of tsunami deposits from other sources such as storms is still lacking, establishing these criteria is essential if we are to improve our understanding of tsunami frequency over geological timescales. By this means we will improve the identification of tsunami hazard and improve risk assessment. This special issue focuses on tsunami deposits, identifying their characteristics and their discriminating features from other sources such as storms. Although perhaps not as common as other 'event' sediments, it is considered likely that a reappraisal of the geological record is required to place them in their representative context.