EVENT SUMMARY - POST-TSUNAMI SURVEY (ITST-Tonga, Journal, Report, web summary)
EVENT SUMMARY - POSTER (A4 low-res, A0 high-res)  
  Hunga-Tonga Hunga Ha'apai Eruption and Tsunami: Importance of Real-time Sea Level Data 
  for Tsunami Warning Decision-making 

The Hunga-Tonga Hunga-Ha‘apai (HTHH) volcano, located 60 kilometres northwest of Tongatapu, Tonga began erupting at 407 UTC on 15 January 2022 based on Himawari-8 satellite images, with a massive explosive eruption at 0414 UTC from seismic data.  The eruption triggered a tsunami that caused damage locally, regionally, and across the Pacific.   The local tsunami killed three people and caused major destruction to many low-lying coastal communities on Tongatapu, ‘Eua and the Ha‘apai Group of Tonga; runups up to 15 m and 500 m inundation were reported for Mango Island by the Tonga Geological Services (TGS).

Elsewhere waves up to 2 m in amplitude were reported by the Pacific Tsunami Warning Centre (PTWC). To save lives, countries issued warning and advisory alerts, and in some places evacuated coastal populations. Many countries experienced waves greater than 0.3 meter in amplitude, which typically triggers marine advisories recommending to citizens to stay out of the water as strong currents and/or unusual waves may occur.  Damaging waves struck harbours and coasts in New Zealand, Rarotonga, Hawaii and the US west Coast, and as far away as Peru (additionally, two deaths occurred), Chile in the eastern Pacific, and Japan in the northwestern Pacific. Altogether, the PTWC issued 12 bulletins over a 20-hour time span and reported 117 tsunami wave measurements from 26 countries.

The gigantic eruption obliterated the volcanic cone-caldera complex that had grown connecting the two islands, generating an atmospheric disturbance that extended into the stratosphere and that was observed by international satellites. The multiple explosions were heard loudly not only on the Tonga islands, but also in Fiji and American Samoa. The resulting shockwaves were measured on barometers as they traversed the globe. The coupling of the air wave with the ocean surface generated small waves (meteotsunamis) observed in the Pacific and also on coastal gauges in the Caribbean and across the Atlantic in the Azores and Madeira, and as far as Cabo Verde as well as in the Indian Ocean in Mauritius.

Previous eruptions were in March 2009 and November-December 2014, but none of them generated tsunamis. The volcanic activity resumed in December 2021. On 13 January, a smaller eruption occurred for which the Tonga NTWC issued a tsunami advisory lasting about one day – the advisory was cancelled at 1102 local time. Unfortunately, while the potential for continued volcanic activity was expected, a massive explosion was not expected.

This is the first time that the PTWS has had to respond to a destructive volcanic event of these characteristics as the PTWS has primarily focused on earthquake-generated tsunamis that cause nearly 90% of the world’s tsunamis. To move forward, the PTWS is immediately convening Post-Event Briefs to share information and experience, and provide interim guidance should another volcanic eruption occur.

PTWS Post-event Brief I: 20 January 2022, 2200-2400 UTC (virtual)
PTWS Post-event Brief II: 03 February 2022, 2200-2400 UTC (virtual)
PTWS Post-event Brief III: 10 February 2022, 2200-2400 UTC (virtual)