NSFGEO-NERC: Tsunamis from large volume eruptions

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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.