Hunga Tonga Eruption 2022: What Happened and Why It Mattered

On 15 January 2022, the underwater Hunga Tonga–Hunga Ha'apai volcano in Tonga produced the most powerful volcanic eruption of the 21st century so far. Its plume climbed about 57 km, the highest ever measured by satellite, and the blast sent an atmospheric pressure wave around the planet several times. A tsunami swept across the Pacific, reaching Tonga within minutes and Australia's east coast within hours.

This article explains what happened, why the eruption was so violent, how it affected Australia, and what it taught scientists about volcanoes, weather and tsunami warnings.

What happened during the Hunga Tonga eruption?

The volcano sits about 65 km north of Tonga's capital, Nuku'alofa. It became active again on 20 December 2021, building ash plumes over the following weeks. A large explosion on 14 January sent ash about 20 km high.

The climactic eruption began around 5:15 pm local time on 15 January (about 2:15 pm AEDT). Within an hour, the umbrella cloud spread hundreds of kilometres across the South Pacific, and lightning sensors recorded hundreds of thousands of strikes.

Key facts at a glance

• Date: 15 January 2022 (climax about 5:15 pm Tonga time)

• Plume height: about 57 km, reaching the mesosphere (NASA)

• Pressure wave: circled Earth at least four times (WMO, NOAA)

• Water vapour: an estimated 146 million tonnes injected into the stratosphere (NASA)

• Deaths: at least four in Tonga and two in Peru, with more indirect losses reported

Why was the eruption so explosive?

The vent sat roughly 150 m below sea level. When hot magma met seawater at that depth, the water flashed to steam and shattered the magma into fine ash. This interaction, known as a phreatomagmatic or Surtseyan eruption, released energy far faster than a typical land eruption.

Scientists estimate the explosion was equivalent to several to tens of megatonnes of TNT. Most of the volcano's central cone collapsed, leaving a caldera hundreds of metres deeper than before.

The atmospheric pressure wave

The blast created a Lamb wave, a pressure pulse that travelled along Earth's surface at close to the speed of sound. Barometers worldwide recorded it, including Bureau of Meteorology (BOM) stations across Australia, which showed a sudden pressure jump of a few hectopascals on the evening of 15 January.

The wave passed over Australia several times over the following days. The boom was heard as far away as Alaska, roughly 9,000 km from Tonga.

A Pacific-wide tsunami

The eruption generated two types of tsunami. The first came from the explosion and collapse near the volcano, with waves up to around 15 m striking parts of Tonga. The second was a "meteotsunami" driven by the pressure wave, which moved faster than a normal tsunami and raised sea levels across the Pacific and even the Caribbean.

Where the tsunami reached

• Tonga: severe coastal damage, homes destroyed on outer islands and ash covering Tongatapu

• Fiji and Vanuatu: coastal flooding and evacuations

• New Zealand: surges damaged boats and marinas in Northland

• Japan: waves over 1 m, earlier than expected because of the pressure wave

• Peru: two people drowned and an oil spill occurred at a refinery terminal

Impacts on Tonga

The eruption cut Tonga's only international undersea internet cable, isolating the country for days. Ash contaminated water supplies and crops, and international relief was delivered under strict COVID-19 protocols. Full internet access took about five weeks to restore.

How the eruption affected Australia

BOM issued a marine and land tsunami threat for Lord Howe Island and marine threats for Norfolk Island and parts of the New South Wales, Queensland, Victoria and Tasmanian coasts. Unusual currents and surges were observed at several harbours, and some beaches were closed as a precaution.

Australian weather stations also recorded the pressure wave, giving forecasters a rare look at a global atmospheric signal. Learn more about how alerts work on our tsunami warnings page.

Climate effects of the stratospheric water vapour

Unlike most large eruptions, Hunga Tonga released relatively little sulfur dioxide but an enormous amount of water vapour, boosting stratospheric water by roughly 10%. Water vapour traps heat, so researchers expected a small, temporary warming influence rather than the cooling seen after eruptions such as Pinatubo in 1991.

Later studies suggest the net effect on global temperatures has been small and the vapour also affected ozone chemistry over the Southern Hemisphere. Research into these effects is ongoing.

Lessons for warnings and science

• Tsunami warning systems were designed mainly for earthquakes, so volcanic and pressure-wave tsunamis need new detection methods.

• Satellites, lightning networks and barometers together tracked the eruption in near real time.

• Remote Pacific nations need backup communications when undersea cables fail.

For other natural hazards around our region, see the earthquake hub and recent Australian earthquakes map.

Sources

• NASA – Tonga eruption blasted unprecedented amount of water into stratosphere

• USGS Volcano Hazards Program

• World Meteorological Organization

• Bureau of Meteorology – Tsunami warnings