NSFGEO-NERC: Tsunamis from large volume eruptions

The greatest loss of life from any historic volcanic eruption-generated tsunami was in 1883 when the Krakatau volcano in Indonesia erupted. During this large-volume, caldera-forming event, multiple, volcanically-triggered tsunamis were generated which, on striking the adjacent coasts of Java and Sumatra, killed approximately 33,000 people. The proposed tsunami generation mechanisms include pyroclastic density flows produced from collapsing eruption columns, explosions, caldera collapse and a lateral blast. Yet, despite numerous published papers on the relative contributions to the tsunami from these mechanisms, they are still not clearly identified or defined, and have been a source of speculation and controversy for over 130 years.

In this multi-disciplinary study, the research on the Krakatau will improve our understanding of tsunamis generated by volcanic eruptions, especially those from large-volume, caldera-forming events which, because of their proximity to the sea, have the potential to generate devastating tsunamis. As a large-volume, caldera-forming event Krakatau is representative of other, similar examples, such as Santorini (southern Aegean) in 3500 BP and Kikai (Japan) in 7500 BP. Like these older, prehistoric events, the Krakatau eruption includes diverse tsunami generating mechanisms including pyroclastic density current (PDC) discharges into the sea, caldera collapse, and explosions. One of the critical aspects of Krakatau, which single it out as the best event to study is the post event survey carried out immediately after the eruption by Verbeek, which describes the eruption and the impact of the eruption and tsunami. These descriptions provide validation of the new numerical tsunami modelling, which is not available from any other analogous event.

The broader background to the research is that new understandings of tsunami generation from other mechanisms, such as earthquakes, landslides, and volcanic collapse, has largely resulted from recent devastating events, such as Papua New Guinea, 1998, the Indian Ocean, 2004, and Japan, 2011. These events have caused over 300,000 fatalities and US$30 billion of damage. Due to the lack of a major recent event, eruption generated tsunamis remain largely unresearched.

This multidisciplinary project therefore, will address a major knowledge gap in non-seismic mechanisms of tsunami generation - tsunamis from volcanic eruptions. Defining eruption mechanisms and their relative contributions in tsunami generation is essential to the development of robust numerical tsunami models. The first challenge, therefore is to identify the most likely tsunami mechanisms. Although, there is uncertainty over these mechanisms, the most likely are caldera collapse and the entry into the sea of pyroclastic density currents (PDCs). To identify the mechanisms that underpin the tsunami models there are number of additional challenges. The volcanic PDC deposits and the caldera collapse will be mapped out during a marine survey around Krakatau Island. There will be new numerical modelling of how pyroclastic density currents enter the sea and new numerical models of tsunami generation from pyroclastic density flows and caldera collapse. The numerical tsunami models will be validated by field work to research sediments deposited as the tsunami flooded the coast.

There are over 425 active volcanoes located within 5 km of the sea, of which 60 are collapse calderas and 35 marine and direct analogues to Krakatau. Tsunamis associated with volcanoes and volcanic eruptions have resulted in tens of thousands of fatalities during the last two centuries and pose significant hazards to rapidly growing coastal populations in volcanically active areas around the world. Without a recent catastrophe, the hazard from eruption-generated tsunami has been overlooked, resulting in the regions' most vulnerable to these events: the Pacific, Caribbean and Mediterranean being rather unprepared for their impact. Yet the hazard is very real, although the last major eruption-generated event was Krakatau, they have a frequency of ~100 years.

On the basis of the above, the research will benefit both scientists and stakeholders, for example, Earth Scientists, tsunami modellers, risk managers, NGOs. In the first instance the study will be of great importance to Indonesia, where the risk of volcanic eruption and tsunami hazards is considerable. Further, the project and results will be of worldwide interest, and result in renewed emphasis on the hazard from other caldera-collapse volcanoes that have potential to generate tsunamis.

In Indonesia, the outputs will feed directly into the improvement of hazard and risk assessments and scenario planning relating to potential future volcanic and tsunami activity, specifically, successful realisation of project aims and objectives through collaborative disaster risk reduction under the Newton Fund now being organised by Tappin and colleagues for Indonesia. Within the USA it would have an immediate impact on the caldera-collapse volcanos of the Aleutian Arc with input into mitigation programmes by Co-Pi Grilli through the US National Tsunami Hazards Mitigation Programme of which he is the lead on tsunami hazard.

Co-Pi Tappin, has been working on the tsunami hazard from Santorini volcano in the Aegean, which explosively erupted in 3500 BP with devastating impact. Within the Aegean, after the recent volcanic activity on Santorini Island, mitigation plans are being formulated for future eruptions, and this research will add to these by addressing tsunami hazard (see letter of support from Athens University). The research will provide direct evidence on the potential impact of caldera-collapse tsunamis across the Eastern Mediterranean. Through our Greek project Partner, the results will be available to inform decision-making and scientific-advisory bodies regionally/nationally in Greece, including the Earthquake Planning and Protection Organization (EPPO) (responsible for evaluating volcanic hazards and determining the response to events at Aegean volcanoes), the Institute for the Study and Monitoring of Santorini Volcano (ISMOSAV), the National Observatory of Athens, the Greek National Committee for the Monitoring of Santorini Volcano and the Mayor of Santorini.

We will also promote our results to the Caribbean, through our contacts in UNESCO/IOC. Tappin has recently attended meetings on this region that demonstrate the lack of recognition of this hazard here and S. Grilli regularly meets the NTHMP and IOC representatives in charge of the Caribbean. Our results will enable these mitigation agencies and individuals with interests in tsunami to enhance and strengthen hazard assessments and disaster management plans.

Media dissemination: An important aspect of project impact is the timely dissemination of project results, which will be through a project website and blog. The proposed work clearly has the potential for attracting the interest of scientific documentary producers. PIs S. Grilli, Tappin and Day have a long record of being featured in scientifically oriented media (National Geographic, PBS-Nova, BBC, Discovery and History channels). As work progresses, active steps will be taken to attract media to produce a documentary.