PTWC HTHH Interim Procedures and PTWS Products

On the afternoon of 15 January 2022, the Hunga Tonga – Hunga Ha’apai (HTHH) Volcano, located about 70 km northeast of Tongatapu, Tonga, violently erupted. The massive explosion, at about 4:14 UTC, generated a tsunami that caused damages locally, regionally, and across the Pacific. International satellites captured the gigantic explosion, and countries in the region heard the loud blasts.  The eruption severed the fiber optic communication cable between Tonga and Fiji at about 05:30 UTC, resulting in the near-complete communication blackout between Tonga and the outside world until 22 February 2022 when the cable was repaired.

Tsunami wave runups up to 20 m high and inundation over 1000 m inland were measured in the Tongatapu Islands, ‘Eua, and Ha’apai Islands of Tonga (ITST-Tonga, Post-Tsunami Field Survey), and elsewhere waves runups up to 4 m in the USA and 2 m on sea level gauges in Peru. The explosions also generated a pressure wave that traversed the globe several times, and in some places coupled with the ocean surface to generate small tsunami waves in the Caribbean, Atlantic, and the Indian Ocean

For the Tonga Meteorological Service (TMS, National Tsunami Warning Center), the cable break also cut all tsunami and weather monitoring data streams, such as from the Nuku'alofa sea level gauge and atmospheric satellites, leaving them with extremely-limited satellite phone connectivity, and no live earthquake, tsunami, and volcano information for hazard assessing.Starting from 25 January 2022 when ITIC was first successful in connecting with a poor signal, regular check-ins were convened with TMS and the Tonga Geological Service to enable the NZ GNS and PTWC to provided situational updates; emergency phone alert protocols were established to directly call the TMS.  Through April 2022, more than 30 virtual meetings were convened by ITIC / IOC bringing together seismic, sea level, and volcano international experts to advise and restore their tsunami warning system. Tonga's Post-Tsunami Field Survey for runup and inundation was conducted by Tongan government officials and one international volcano scientist, with remote technical assistance by eCoast NZ, ITIC/IOC, and SPC.

The 15 January HTHH volcano-generated tsunami was the first time that the Pacific Tsunami Warning Center (PTWC) had to respond to such an event since its system is primarily focused on earthquake-generated tsunamis that represent nearly 90% of the past cases of tsunami in the world.

In response the ITIC imemdiately organized and convened three Post-Event Briefs (PEB-I 20 January 2022, PEB-II 3 February, PEB-III 10 February) for Member States of the Intergovernmental Coordination Group (ICG) for the Pacific Tsunami Warning and Mitigation System (PTWS). The Briefs shared information and experience, and discussed interim guidance should another volcanic eruption occur. The Kingdom of Tonga was able to share its report and recommendations at PEB-II, with minimal communication bandwidth.

At PEB-III, the ICG/PTWS established a Task Team on Hunga-Tonga Hunga-Ha’apai (HTHH) Volcano Tsunami Hazard Response under PTWS Working Group 2 to provide guidance to the Pacific Tsunami Warning Center (PTWC) for the immediate development of interim Standard Operating Procedures (SOP) for responding to the possibility of future tsunamis originating from volcanic eruptions or processes similar to the HTHH event. These SOPs became effective on 15 March 2022 through IOC Circular Letter 2882, and are carried out by the PTWC acting as a PTWS Tsunami Service Provider (TSP). The PTWC Interim Procedures and PTWS products were reviewed by the members of the PTWS Steering Committee, and subsequently approved by the Chair of the ICG/PTWS on 25 July 2022. IOC Circular Letter 2902 (17 August 2022) provided the PTWC Interim Products and PTWS Products User's Guide.