Why So Few Casualties?

Despite the total destruction of several beach resorts along western Tongatapu and significant inundation along the populated northern coast, only four deaths were attributed to the tsunami. This low number of casualties can be attributed to multiple factors including: the event occurred during the day, the early arrival of moderate tsunami waves prior to the largest and most destructive waves, the marine tsunami warning issued the day prior by Tonga Meteorological Services, the lack of tourists in Tonga, and the effectiveness of tsunami awareness education and outreach campaigns conducted since the 2009 Samoa-Tonga tsunami hit Niuatoputapu, Tonga causing nine deaths.

The occurrence of the tsunami during daylight hours on a sunny weekend afternoon likely helped to reduce the number of casualties. People were out and about, generally aware of their environment and able to react despite the lack of at least one of the normally discussed ‘natural warnings’ associated with tsunami disasters, i.e. strong ground shaking. In addition, there was a generally heightened awareness of the possibility of tsunami, because in the previous few weeks several eruptions of Hunga were witnessed and reported in news media. This is in contrast to the effects of the 2010 southern Mentawai earthquake and tsunami an event which occurred at night, during a period of unsettled and rainy weather. The causative earthquake was also anomalous in that it only caused weak ground shaking and residents did not generally feel the need to spontaneously evacuate. Ultimately a tsunami with heights greater than 10 m tore through numerous coastal villages causing hundreds of deaths (Hill et al., 2012).

The early tsunami waves were also an important mitigating factor for the residents of the western coast of Tongatapu. Based on information from eyewitnesses, the first waves arrived largely without warning. These waves were large enough to inundate the western beaches and penetrate to the boundaries of the coastal properties, but they did not cause extensive inundation or damage. It was the effect of these waves that prompted the locals into action to evacuate guests and staff from the resorts. The loud booms following the arrival of the first waves as well as the atmospheric pressure fluctuations, i.e., “popping ears” then prompted people to accelerate their evacuation to higher ground. Due to the quick response following the initial surges, by the time the larger and more destructive waves arrived, the evacuation was well under way, allowing locals to get out of the area and reach high ground or elevated vantage points.

The eruption on 14th January 2022 (the day prior to the main eruption) also played a significant role in highlighting of the possibility of a tsunami being generated by a large eruption. The Tonga Meteorological service issued a Marine Tsunami Warning on the morning of the 14th which was circulated through radio and news outlets. While all tsunami warnings had been cancelled on the morning of the 15th, these warnings raised awareness in the coastal communities. Following the loud booms and observation of the ash column an urgent tsunami evacuation warning was issued and immediately played on AM radio at 425 UTC. This likely gave confirmation to those already evacuating and an additional nudge for others.

Another mitigating factor was the complete absence of international tourists in Tonga due to travel restrictions from the ongoing COVID-19 pandemic. Although resorts on the west coast were operating, they were at reduced capacity and catering only to domestic patrons. Despite this, the tsunami struck on a fine weekend, when domestic usage of beach and resort areas was highest.

The Government of Tonga and other international agencies can be credited with reducing tsunami casualties through their ongoing efforts of tsunami hazard mitigation through education and outreach. These efforts have been steadily increasing world-wide since the 2004 Indian Ocean tsunami and were significantly ramped up in Pacific Island nations following the 2009 Samoa-Tonga earthquake and tsunami. One initiative in particular, World Tsunami Awareness Day (WTAD), designated as the 5th of November each year by the UN General Assembly in 2015, may have been particularly beneficial to reducing casualties during the January 15th event. In Tonga, WTAD was commemorated through a series of educational and outreach initiatives just 2.5 months before the Hunga-Tonga event. Activities included art and poetry competitions and exhibitions in schools, discussions on Tongan radio stations, prayers and reminders during church services on the Sunday prior to WTAD, and a series of activities on the day itself – although this event was held a week later due to a COVID lockdown that was in effect on November 5th.