After the destructive tsunamis in Greenland in 2017 and Indonesia (Palu and Anak Krakatau

separate events) in 2018 that were generated by landslides, volcanic eruptions and earthquakes outside subduction zones, the Intergovernmental Oceanographic Commisssion (IOC) of UNESCO Working Group on Tsunamis and Other hazards related to sea level Warning and mitigation Systems (TOWS-WG) identified the need to provide to Member States a report summarising relevant information and knowledge on tsunami warning systems for tsunami events generated by nonsesismic and complex sources. Such tsunamis have made up 13% of the world’s confirmed tsunamis. Non-seismic and complex sources of tsunamis include volcanic sources, such as underwater explosions, pyroclastic flows, large scale collapses, etc., subaerial and underwater landslides, and tsunamis triggered by atmospheric perturbations (meteotsunamis).

 

In 2020, an Ad Hoc Team on Atypical Tsunamis was established by the TOWS-WG Task Team on Tsunami Watch Operations (TT-TWO). The mandate of the team was to investigate tsunamis generated by non-seismic and complex sources, document the current state of monitoring and warning for such events, and provide guidance and recommendation to IOC Member States. The ad hoc team presented its final report on February 2022, which was accepted by the TT-TWO Task Team and endorsed by the 15th Session of the TOWS-WG.

On 15 January 2022, the eruption of the Hunga Tonga Hunga A’Apai (HTHH) volcano caused both a local and a global tsunami with fatalities in Tonga and Peru. This highlighted to the world the power of volcanic tsunamis and the difficulties in monitoring and warning for these events. In response to this, in February 2022 the TT TWO decided to establish a new Ad Hoc Team on Tsunamis Generated by Volcanoes (TGV Team). The purpose of this team was, as recommended by IOC 31st General Assembly in 2021, to specifically document the current state of monitoring and warning of volcanic tsunamis and provide guidance to Member States and the IOC on this topic.

 

This report is the culmination of that work and provides an overview of how volcanos can generate tsunamis, modelling techniques specific to volcanic tsunamis, requirements and examples of monitoring and warning systems, and finally recommendations for the future.