updated on 5 January 2019

Introduction

On 22 December 2018 (~21:00 local time, ~14:00 UTC), large tsunamis were generated at Sunda Straits, Indonesia, and they caused a great disaster along the coasts of the western Java and the eastern Sumatra. According to PVMBG*1, the Anak Krakatau Volcano that has continued the eruptive activity in recent years was partially collapsed, and tsunamis might be triggered by this event. After the collapse, Anak Krakatau still continues the eruptive activity, thus the current situation is carefully monitored by Indonesian authorities. The volume of collapsed material, the sequence of the event, tsunami generation and propagation processes, and their relationship to the eruptive activity are still unclear, although they are important to understand nature, dynamics, and hazards of volcanic edifice collapses. Also, unveiling this event will contribute to understand similar examples in Japan. Here, we report our preliminary results of numerical simulation of tsunamis and volcanic edifice collapse of Anak Krakatau.
Anak Krakatau is the small volcanic island that grew after the disastrous caldera-forming eruption in 1883 at this area (Figs. 1, 2).Before the collapse on 22 December 2018, the size of the island was ~2.1 km EW and ~2.3 km NS. The volcano consists of lava flows and a central cone, with an altitude >300 m above sea level (Fig. 3). The SW slope of the edifice was very steep, extending to the caldera floor ~270 m below sea level. The collapse occurred at southwest of the edifice and approximately a half of the island, including the summit area, was lost.

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