Most powerful volcanic eruption recorded with modern equipment

On 15 January 2022, the underwater Hunga Tonga-Hunga Ha’apai volcano erupted with an energy equivalent estimated at between 15 and 200 megatons of TNT. Some studies have given the event a rating of between VEI-5 and VEI-6 on the Volcanic Explosivity Index, which calculates the relative impact of volcanic eruptions on a scale from 0 to 8; others have rated it at VEI 4. Its precise magnitude aside, there is one thing that all scientists can agree on: this was the largest recorded eruption on Earth since that of Krakatoa in Indonesia in 1883; although assessed without the accurate tools we have today, Krakatoa is estimated to have been a VEI-6 event with a comparable explosivity to the upper predictions for Hunga Tonga-Hunga Ha’apai (i.e., 200 megatons of TNT).

Scientists studied the eruption using a combination of technologies – including satellite data, high-resolution digital elevation models and on-site field and drone surveys – to generate tsunami simulations and arrive at their conclusions.

Even at a yield of 15 megatons (as reported in Science Advances on 14 April 2023), the Hunga Tonga-Hunga Ha’apai eruption is comparable to the USA’s largest-ever atomic bomb test on 1 March 1954, which was staged on Bikini Atoll, part of the Marshall Islands in the Pacific Ocean. This is about 1,000 times greater than the bomb that was dropped on Hiroshima, Japan, on 6 August 1945. A yield of 61 megatons (as reported in Shock Waves on 9 August 2022) would be higher than that of the largest nuclear explosion, that of the former USSR’s Tsar Bomba in the Novaya Zemlya area on 30 October 1961.

The cataclysmic eruption of Krakatoa on 26–27 August 1883 claimed around 36,000 lives. Thankfully, this more recent event was far less deadly. Although the resultant megatsunami devastated some parts of Tonga, there were only a handful of fatalities. The surprisingly low loss of life has been attributed to several factors, including the rapid reaction of the local communities and low tourist numbers owing to the COVID-19 pandemic. Tonga’s main city, Nuku’alofa, was protected by its location behind an island in a lagoon, although the megatsunami – which generated waves that peaked at a height of around 90 m (295 ft) – caused the deaths of two people in Peru, around 10,000 km (6,200 mi) away.