Tonga undersea volcanic eruption unlikely to have long-term climate impact 

Eruption of the Hunga-Tonga-Hunga-Ha’apai volcano in the South Pacific, 65 km north of Tongatapu, Tonga, on January 15 is unlikely to have long-term climate impact, according to Temblor, a US-based catastrophe modeling company specialising in seismic hazard and risk assessment.

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It is likely, however, that the islands have experienced many inches of ash fall as well as damage from a resultant tsunami, which inundated coastal areas, a Temblor analysis quoted the Pacific Tsunami Warning Centre as saying.

Workers clean an oil spill caused by abnormal waves, triggered by a massive underwater volcanic eruption in Tonga, off the coast of Lima, in Ventanilla, Peru January 19, 2022 | Photo Credit: REUTERS/Angela Ponce

The eruption was heard in New Zealand. The shock wave was violent enough to shake houses in Fiji, more than 720 km away from Tonga. (Edmonds, M., 2021, Hunga-Tonga-Hunga-Ha’apai in the South Pacific erupts violently, Temblor: http://doi.org/10.32858/temblor.231 ).

Global cooling pattern

The eruption was so powerful it destroyed the subaerial part of the volcano that had been built up in successive eruptions since 2015, according to the Smithsonian’s Global Volcanism Programme. 

Past large explosive eruptions have typically been associated with global cooling. Sulfur dioxide (SO2) injected into the stratosphere – the second layer of the atmosphere – forms sulfate aerosol when it reacts with water, which absorbs and scatters incoming solar radiation, thereby cooling the Earth’s surface.

An eruption occurs at the underwater volcano Hunga Tonga-Hunga Ha’apai off Tonga, January 14, 2022 in this screen grab obtained from a social media video. Video recorded January 14, 2022.  | Photo Credit: Tonga Geological Services/via REUTERS

The ash has dispersed from the caldera (a large cauldron-like hollow that forms after the eruption) but finer particles may stay aloft in the atmosphere and remain there for months or years. The eruption produced around 0.4 teragrams of SO2, data from European Space Agency’s ’(ESA) Sentinel 5P satellite revealed. 

1991 Pinatubo precedent 

In comparison, the 1991 eruption of Pinatubo Volcano in the Philippines emitted around 18-19 teragrams of SO2, which caused cooling of a few tenths of a degree for a few years. So, it is unlikely that the SO2 emitted from the Hunga-Tonga-Hunga-Ha’apai eruption will significantly impact the climate.

The precise magnitude of this eruption will be known once the height of the eruption column as well as the volume of erupted material is estimated, but it is certainly one of the most significant eruptions of the 21st century thus far, the analysis said.

A combination of satellite images shows the Hunga Tonga-Hunga Ha’apai volcano before its main eruption on April 10, 2021 (top) and the same area on January 18, 2022, in Hunga-Tonga-Hunga-Ha’apai, Tonga. | Photo Credit: Maxar Technologies/Handout via REUTERS

Pressure surges from the atmospheric perturbation caused were felt right across the world. Atmospheric pressure fluctuations have been reported in New Zealand, the US, Brazil, Japan and Europe.

More than 14 hours after the eruption, the UK Meteorological Office picked up several pressure waves, more than 16,093 km away from the volcano. It described the waves as ‘like dropping a pebble in a still pond and seeing the ripples.’

Rapid shock wave 

The energy released in the eruption was equivalent to a magnitude-5.8 earthquake at the surface, according to the US Geological Survey. It was captured on satellite images, which showed a shock wave and a rapidly expanding ash cloud that reached 20 km into the atmosphere, the Temblor analysis said. 

A plume rises over Tonga when the underwater volcano Hunga Tonga-Hunga Ha’apai erupted in this satellite image taken by Himawari-8, a Japanese weather satellite operated by Japan Meteorological Agency, on January 15, 2022 and released by National Institute of Information and Communications Technology (NICT) and obtained by Reuters on January 16, 2022. | Photo Credit: National Institute of Information and Communications Technology (NICT)/Handout via REUTERS

Radar images from ESA’s Sentinel-2 satellite show that the island has largely disappeared following the eruption; only the far southwestern and northeastern tips remain.

The Hunga-Tonga-Hunga-Ha’apai volcano lies along the Tonga-Kermedec Arc, where two tectonic plates in the South-West Pacific converge, Temblor explained. It is one of a chain of largely submarine volcanoes that extend all the way from New Zealand to Fiji. 

Notoriously explosive eruptions

Here, the Pacific plate subducts beneath the Indo-Australian plate. As it sinks, the Pacific Plate heats up, releasing fluids into the overlying rocks, which causes them to melt. The magma rises into the overlying crust and some erupts at the surface. 

Eruptions from subduction zone volcanoes are notoriously explosive because magmas there are sticky and contain large quantities of dissolved water from the mantle, which is the explosion’s ‘fuel,’ Temblor points out.

Japan Self-Defense Forces officers load relief supplies for a C-130 Hercules, to be deployed to Tonga with aid to help out the country devastated by a nearby eruption and tsunami, at Komaki air base in Komaki, Japan, January 20, 2022 | Photo Credit: Kyodo/via REUTERS

For submarine volcanic eruptions, however, there is an added ingredient that renders them extra-violent. During large volcanic eruptions a caldera can form due to the void left in the ground by the erupted magma. Calderas on the seafloor can cause tsunamis and large earthquakes when large rock masses sink during the eruption.

‘Hydrovolcanic eruptions’

Seawater can flow into the faults and fractures that form around the edges of the caldera. If water comes into contact with hot magma, it flash-boils into steam, which expands rapidly, adding to the explosive power of an eruption. 

Aircrew work onboard a New Zealand Defence Force P-3K2 Orion during a surveillance flight to assess the damage to Tonga after the Pacific island nation was hit by a tsunami triggered by a massive undersea volcanic eruption January 17, 2022. | Photo Credit: New Zealand Defence Force/Handout via REUTERS

Such eruptions are termed ‘hydrovolcanic.’ They generate powerful base surges – or pyroclastic flows – that expand out from the base of the eruption column, and travel long distances.

A famous example is the 1883 eruption of Krakatoa Volcano in Indonesia. The sound of the volcano explosion was heard 3,000 km away. Large tsunami waves and pyroclastic surges that travelled 40 km over the surface of the sea had killed more than 36,000 people.