Is Bangkok at risk of marine flooding? Evidence relating to the historical floods of AD 1785 and 1983

© 2020, Springer Nature B.V. Thailand’s low-lying capital city Bangkok is a dense metropolis, one of Asia’s rapidly growing ‘megacities’, and home to over 10 million residents. Bangkok’s location on the sinking Chao Phraya Delta means it has a high susceptibility to river flooding. However, the possible contribution of marine incursion to river flooding is not as widely recognised and needs further consideration. We therefore re-examine the historically documented floods in AD 1785 and 1983. Available evidence suggests that the superposition of different flood behaviours was important during both events. Attention is drawn to the evidence for, and contributory roles played by, astronomical spring tides, meteorological tides, storm waves and possibly storm surge. These marine effects can exacerbate river floods caused by seasonal peak flows in the tidal lower Chao Phraya River during the early north-east monsoon. For future management of flood risk, it is therefore necessary to recognise that Bangkok has a compound flood-risk profile that includes both hydrometeorological and marine influences. The significance of marine influences on Bangkok’s flood risk is likely to increase in future with continuing eustatic sea-level rise and subsidence of the Chao Phraya Delta

Past and potential tsunami sources in the South China Sea: A brief synthesis

© 2017 Elsevier B.V. Extending across some 3.5 million square km and with coastlines populated by in excess of 80 million people, the South China Sea (SCS) is bordered by seven independent states. Understanding the risk of tsunamis in the SCS is therefore an imperative, especially given the new priorities for the science community following the endorsement by the UN General Assembly of the Sendai Framework for Disaster Risk Reduction 2015–2030. Our review presents a synthesis of existing literature on the current state of knowledge concerning known tsunamigenic threats, but also highlights a number of other potential sources that have so far received less attention or gone largely un- or under-recognised. An overview of the geological evolution of the SCS is presented in order to appreciate how the existing structural configuration of the ocean basin is responsible for the presence of a variety of potential tsunamigenic mechanisms. Traditional thinking places the generation of a large-magnitude earthquake at the Manila trench subduction zone at the top of the spectrum for tsunami potential, with several simulations already available in the literature illustrating wave characteristics resulting from the worst-case rupture. In addition to the Manila trench and other possible earthquake sources, however, volcanic activity and submarine landsliding of sediment burden on continental shelves on the SCS margins represent hitherto fundamentally unquantified tsunami threats, although revealed nonetheless by, for example, the existence of the giant Brunei and Baiyun submarine slides. Furthermore, in the central SCS, previously considered essentially devoid of tsunami sources, numerous near-surface carbonate platforms and coral atolls show evidence of arcuate bight-like structures in their planform geometry, likewise suggesting their propensity for possible tsunamigenic lateral flank collapse. In the current absence of well-constrained tsunami probability estimates and scenarios of wave size and propagation features for non-earthquake tsunami sources, future research priorities lie in two main areas. These are, 1. improvement of modelling for tsunamigenic submarine failures as well as for earthquakes; and 2. a greater focus on geomorphic investigation to identify palaeotsunami deposits on coastlines considered likely to have been impacted in the past and where good preservation potential exists. This is needed to establish the magnitude–timing–frequency of events on Holocene timescales (the last 10,000 years) well beyond historical records, thereby improving our capabilities for understanding and forecasting the likelihood and severity of future tsunami risk in the South China Sea

Short communication: Recognising the perils of landslide-generated tsunamis in the Asia–Pacific region

© 2019, Springer Nature B.V. Two recent tsunamis in Indonesia highlight the importance of submarine landslides. Although both events had different origins (volcanic, seismic), submarine landsliding was probably the key component in tsunamigenesis. While a few recent submarine landslide-generated tsunamis have been discussed in the literature, these types of events have not been seriously scrutinised by geoscientists or hazard modellers. This is most likely because of both a lack of awareness and also the common perception that such events are too remote a possibility to be of major concern. However, by catching us off-guard, these two Indonesian events have brought slope-failure tsunamigenesis into sharper focus. It is hoped that this will stimulate greater scholarship on the issue of slope-failure tsunamigenesis worldwide, with an aim to better understanding event characteristics, probabilities, and ultimately better inform existing risk reduction strategies

Tonga volcanic eruption and tsunami, January 2022: globally the most significant opportunity to observe an explosive and tsunamigenic submarine eruption since AD 1883 Krakatau

January 2022 witnessed the violent eruption of Hunga Tonga–Hunga Haʻapai submarine volcano in the South Pacific. With a volcanic explosivity index possibly equivalent to VEI 5, this represents the largest seaborne eruption for nearly one and a half centuries since Indonesia’s cataclysmic explosion of Krakatau in AD 1883. The Tongan eruption remarkably produced ocean-wide tsunamis, never documented before in the Pacific instrumental record. Volcanically generated tsunamis have been referred to as a ‘blind spot’ in our understanding of tsunami hazards, particularly in the Pacific Ocean. This event therefore presents a unique opportunity for investigating the multiple processes contributing to volcanic tsunamigenesis. It is argued that, although challenges exist, integrating theoretical, observational, field and modelling techniques offers the best approach to improving volcanic tsunami hazard assessment across Oceania

Applying cellular automata to dynamic simulation of a tsunamigenic submarine landslide in the South China Sea

This work presents the first known application of a new approach to tsunami modelling, by linking a discrete cellular automata (CA) dynamic model of a submarine landslide to an off-the-shelf tsunami modelling package. This has the advantage of simulating the temporal evolution of the submarine landslide rather than as a single rigid sliding mass. We first tested that the coupled model was able to satisfactorily reproduce observed tsunami wave heights resulting from the flank collapse of the Anak Krakatau volcano in the Sunda Strait (Indonesia) in December 2018, before applying it to a speculative area of interest on the North Borneo (Continental) Shelf (NBS). The NBS has one of the thickest near-shore clastic sediment wedges known globally (12 km thickness) and a very long pre-history of submarine landsliding. We modelled a small slide (5 km3 volume) because this is far more likely to occur than a recurrence of the gigantic Brunei slide (1200 km3 volume). Results indicate that a 5 km3 submarine landslide generates multiple tsunami waves, the largest of which reached 8 m at the coast of nearby Balabac Island (The Philippines). Small tsunami waves also arrived on the central Vietnam coast, more than 900 km distant. A larger potential failure on the NBS therefore appears capable of causing a tsunami with greater runup heights, which could pose a risk to much of central and southern Vietnam, northern Borneo (Sabah, Brunei) and Palawan. Finally, we note that the South China Sea is fringed by a necklace of other thick offshore clastic sediment accumulations, most notably on the southern China continental margin, offshore southern Taiwan, and offshore central Vietnam. Given the proof-of-concept of our coupled CA–tsunami modelling approach described here, we recommend this also be applied in these areas to assess the risk posed by a wide range of submarine landslides to coastal populations and infrastructural assets (including nuclear power plants)

Tsunami damage to ports : cataloguing damage to create fragility functions from the 2011 Tohoku event

Modern tsunami events have highlighted the vulnerability of port structures to these high-impact but infrequent occurrences. However, port planning rarely includes adaptation measures to address tsunami hazards. The 2011 Tohoku tsunami presented us with an opportunity to characterise the vulnerability of port industries to tsunami impacts. Here, we provide a spatial assessment and photographic interpretation of freely available data sources. Approximately 5000 port structures were assessed for damage and stored in a database. Using the newly developed damage database, tsunami damage is quantified statistically for the first time, through the development of damage fragility functions for eight common port industries. In contrast to tsunami damage fragility functions produced for buildings from an existing damage database, our fragility functions showed higher prediction accuracies (up to 75 % accuracy). Pre-tsunami earthquake damage was also assessed in this study and was found to influence overall damage assessment. The damage database and fragility functions for port industries can inform structural improvements and mitigation plans for ports against future events.Published versionSCOR Asia PacificTokio Marine & Nichido Fire Insurance Co. Ltd.Willis Research Networ