Hunga-Tonga-Hunga-Ha’apai Volcano

The Hunga-Tonga-Hunga-Ha’apai volcano is a large submarine volcano located in the South Pacific Ocean, within the island nation of Tonga. It is part of the highly active Tonga–Kermadec volcanic arc, which forms one of the most dynamic subduction zones on Earth. The volcano is situated about 65 kilometres north of Tonga’s capital, Nuku‘alofa, and is best known for its massive and unusual eruption on 15 January 2022, one of the most powerful volcanic events of the 21st century.

Geological Background

The Hunga-Tonga-Hunga-Ha’apai volcano lies along the convergent boundary where the Pacific Plate subducts beneath the Indo-Australian Plate. This tectonic activity gives rise to intense seismicity and volcanism in the region.
Before the 2022 eruption, the volcano’s activity had created a small landmass connecting the uninhabited islands of Hunga Tonga and Hunga Ha’apai. These islands are the emergent parts of a much larger underwater volcanic edifice that extends approximately 1,800 metres above the seafloor.
The volcano has a history of intermittent explosive eruptions, with recorded events in 1912, 1988, 2009, 2014–2015, and most notably 2021–2022.

The 2021–2022 Eruption Sequence

The eruption sequence began in December 2021, when ash and steam plumes were observed rising several kilometres into the atmosphere. This activity escalated dramatically on 15 January 2022, culminating in a colossal explosion.
Key features of the 2022 eruption include:

• Explosive power: The blast was equivalent to the energy release of several hundred Hiroshima-sized nuclear bombs.
• Atmospheric effects: The eruption sent an ash plume more than 50 kilometres high, penetrating the mesosphere, making it one of the tallest volcanic plumes ever recorded.
• Shock waves: The explosion generated atmospheric pressure waves that travelled around the globe multiple times, detected as far as Europe and the Americas.
• Tsunami: Massive waves, up to 15 metres high in nearby areas, struck Tonga and caused damage across the Pacific, including Japan, Peru, and the United States’ west coast.
• Sound: The eruption’s boom was heard over 10,000 kilometres away, reported in places such as Alaska.

Satellite imagery showed that most of the central volcanic island was obliterated, leaving only small remnants of Hunga Tonga and Hunga Ha’apai above sea level.

Environmental and Human Impact

The eruption had widespread effects:

• Tonga: Heavy ashfall blanketed the islands, contaminating water supplies, destroying crops, and damaging infrastructure. Communications were severely disrupted due to damage to undersea cables.
• Casualties: Dozens of deaths were reported in Tonga and other countries affected by the tsunami.
• Global climate effects: The eruption injected vast amounts of water vapour and ash into the stratosphere. Unlike many explosive eruptions, which cool the Earth by releasing sulphur dioxide, this eruption is believed to have contributed to temporary warming due to the greenhouse effect of excess water vapour.
• Marine ecosystem: Local ecosystems were devastated, with coral reefs and marine life suffering from the combined effects of ash deposition, shock waves, and tsunami surges.

Scientific Significance

The Hunga-Tonga-Hunga-Ha’apai eruption has been described as the most powerful volcanic explosion since the 1883 Krakatoa eruption. It provided valuable insights into volcanic processes, atmospheric science, and tsunami generation.
Key scientific lessons include:

• Volcanic plumes: The eruption demonstrated how submarine volcanoes can generate unprecedented plume heights due to rapid interaction between magma and seawater.
• Atmospheric circulation: The global propagation of shock waves offered rare data for studying atmospheric dynamics.
• Tsunami generation: The event highlighted the complex mechanisms of volcanic tsunamis, which are less predictable than tectonic ones.

Ongoing Monitoring and Risk

The volcano remains active, and monitoring efforts are ongoing through satellite surveillance, ocean-based sensors, and regional seismic networks. Tonga’s remote location and limited monitoring infrastructure make forecasting volcanic activity challenging.
The eruption also raised awareness of the vulnerability of Pacific island nations to natural disasters, highlighting the need for resilient infrastructure, disaster preparedness, and international cooperation in early warning systems.
The Hunga-Tonga-Hunga-Ha’apai volcano stands as a reminder of the immense power of submarine volcanism and its capacity to affect not only local communities but also global atmospheric and climatic systems.