NSFGEO-NERC Caldera-forming eruption-generated tsunamis

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Tsunamis create major geohazards for populated coastal areas, whose mitigation requires understanding of the generation mechanisms. Numerical models of tsunami generation and propagations are used in support of warning systems and for the creation of inundation maps for hazard assessment. Tsunamis can be attributed to seismic (i.e., earthquakes and submarine landslides) or non-seismic sources (i.e., volcanic eruptions). The latter are prevalent in some areas around the world (e.g., Aleutian arc for US West Coast). Our understanding of tsunami generation from mechanisms such as earthquakes, landslides, and volcanic collapse, has largely resulted from devastating events (e.g., Papua New Guinea, 1998; Indian Ocean, 2004; Japan, 2011), which combined have caused over 300,000 fatalities and US $30B of damage. Due to lack of a major recent event, eruption generated tsunamis (the focus of this study) remain largely under-studied. In this multi-disciplinary study, the US/UK team will perform collaborative field and modeling research, to improve our understanding of tsunamis generated by volcanic eruptions, especially those from large-volume, caldera-forming events close to the sea, which are among the most devastating geohazards. Work will focus on the 1883 Krakatau eruption-generated tsunami, which caused over 33,000 fatalities in Indonesia. Although this eruption was well studied, there is still controversy over the tsunami generation mechanism and, since 1883, apart from a surge of interest during its 100-year anniversary, there has been little new data, which would be a basis for a major project on the event. The new understanding/modeling resulting from this project will improve tsunami hazard assessment and warning from such sources, and could improve operational tsunami hazard assessment and inundation mapping work as tsunami warning systems for non-seismic sources with significant implication in population safety. Project results will be disseminated to the scientific and broader communities at professional conferences, in peer-reviewed journals, by building an extensive website (with project metadata, news, podcasts/videos, and auxiliary information), and through the visualization of scientific data (targeting a K-12 audience). A workshop will be organized in Indonesia at the outset to engage local people and scientists (support from Newton funds is being sought). There will be active collaboration with colleagues at Greek/Caribbean/Mediterranean-based institutions/organizations, facing similar eruption-tsunami risks.As a large-volume, caldera-forming event Krakatau is representative of similar other well studied historical events (e.g., 3500BP Santorini and 7500BP Kikai), and includes diverse tsunami generating mechanisms: pyroclastic density current (PDC) discharges into the sea, caldera collapse, and explosions. It also has an exceptional eruption and tsunami record from observations at the time. The objectives of the study are to: 1) apply improved numerical models of tsunamis from volcanic eruption mechanisms (including seafloor deposits), mainly PDC and caldera collapse; 2) perform new field surveys of on land tsunami sediment deposits, to discriminate individual tsunami events and their impact; 3) perform new PDC field surveys, complementing a pilot offshore seismic database showing that individual PDC flows can be identified and mapped, and their runouts and volumes estimated; 4) use these estimates to understand physical properties of PDCs as they enter the sea; and 5) use the new data (sediment, PDC) as a basis for applying the new numerical tsunami models. Tsunami simulations will be carried out iteratively by comparing model outputs (inundation limits, runups; PDC deposits/runouts) with historical documentation of impacted areas along the coasts of Sumatra and Java, and both old and newly acquired PDC and sediment deposit field survey data.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.