Based on data collected by the Geological Service of Tonga, with the assistance of technical experts from New Zealand and the United States, the new report sheds light on the 15 January 2022 tsunami that followed the eruption of the Hunga Tonga and Hunga Ha’apai volcanoes in Tonga.
While tsunamis are mostly generated by earthquakes, over history 6% of tsunamis have been caused by volcanic eruptions. On 15 January 2022 Tonga’s Hunga Volcano erupted in a sudden and explosive way causing a large local tsunami that devastated villages and resorts along the western shore of Tongatapu and in the Ha’apai island group as well as a far-field tsunami that caused damage and deaths thousands of kilometers away.
To mark the first anniversary of the tsunami event, UNESCO and the The Pacific Community are releasing the much awaited Hunga Tonga – Hunga Ha’apai (HTHH) Post-Tsunami Field Survey, compiling critical tsunami runup and inundation measurements, videos and photos, and field observations from the tsunami generated by the 15 January 2022 eruption of the Hunga Tonga and Hunga Ha’apai Volcanoes.
Under normal circumstances, UNESCO’s Intergovernmental Oceanographic Commission (IOC/UNESCO) facilitates International Tsunami Survey Teams (ITST) of international scientists to work with the impacted country to collect tsunami data within the first week or month following a significant tsunami such as 2009 Samoa, 2010 Chile, 2018 Indonesia.
In the case of Tonga in 2022, however, the immediate post-disaster needs of the community and COVID-19 travel restrictions to and within Tonga prevented International Tsunami Survey Teams to deploy and delayed the development of a comprehensive field survey.
The newly unveiled Survey sheds light on important aspects of the 2022 HUNGA TONGA – HUNGA HA’APAI Tsunami, such as:
- Wave runup heights of up to 20 meters on islands to the south, east and north of the volcano suggesting a radially symmetric wave front emanating from the source.
- Extensive coastal inundation and complete overwash of the Hihifo Peninsula on Tongatapu and smaller islands in the Ha’apai such as Kelefesia, Mango and Nomuka-Iki. This overwash caused the near complete destruction of buildings and structures as well as stripping extensive coastal forests to bare sand and causing significant geomorphic change to coastal landforms.
- The relative timing of the tsunami surges, with eyewitness accounts suggesting that the first arriving tsunami waves served as a natural warning and prompted a near complete evacuation of the area prior to the arrival of a larger second surge some 30 minutes later. This was a major factor in the extraordinarily low number of casualties resulting from this event.
- Tales and accounts of survival from residents in western Tongatapu who evacuated as the first waves were coming ashore while ensuring that others were aware of the impending danger and evacuated as well. As well as the remarkable account of a man who survived nearly 30 hours in the water after being washed off a small island during the tsunami.
Post-Tsunami Field Surveys are a critical tsunami mitigation activity. Documentation of the event for lessons learned is essential for improving tsunami preparedness, mitigation, and the warning system. The post-event collection of tsunami wave runups, flow depths, inundation, and damage to the built and natural environment records the quantitative impact. These are complemented by eyewitness descriptions detailing the wave’s arrival (its timing, character, strength, direction, recurrence, etc.), and powerful accounts of people reacting to and escaping the sudden tsunami.
The field survey data were collected by Tongan national teams, led by the Tonga Geological Services, and remotely assisted by international technical experts from New Zealand and the United States. The international efforts were jointly coordinated by The Pacific Community and UNESCO’s Intergovernmental Oceanographic Commission (IOC/UNESCO), through the International Tsunami Information Centre (ITIC), and the IOC Tsunami Unit based in Suva, Fiji.
The Summary Report represents a coordinated, collaborative effort of the Tongan government, the University of Auckland, eCoast Maine Consulting and Research (New Zealand), the Pacific Community (SPC), IOC/UNESCO and its International Tsunami Information Center, the University of Southern California and the Governments of New Zealand and the United States. The cooperation between these organizations enabled the assessment to run relatively smoothly, given the enormous logistical, transportation, and communications challenges.
The IOC/UNESCO International Tsunami Information Centre, the Pacific Community and New Zealand have been working together since the early 2000s in disaster risk reduction and tsunami training – most recently on tsunami inundation modelling for Southwest Pacific countries and tsunami warning centre operations for Tonga in 2019.
A scientific journal paper based on this report and containing additional insight and analysis has also been recently published in Pure and Applied Geophysics and is available as open access at the link below.
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