Hunga Tonga–Hunga Ha'apai volcano
Hunga Tonga–Hunga Haʻapai is a submarine volcano in the South Pacific.
It is part of the highly active Kermadec-Tonga subduction zone and its associated volcanic arc, which extends from New Zealand north-northeast to Fiji, and is formed by the subduction of the Pacific Plate under the Indo-Australian Plate.
It lies about 100 km above a very active seismic zone.
The volcano rises around 2,000 m from the seafloor and has a caldera which – on the eve of the 2022 eruption – was roughly 150 m below sea level and 4 km at its widest extent.
The only major above-water part of the volcano are the twin uninhabited islands of Hunga Tonga and Hunga Haʻapai, which are respectively part of the northern and western rim of the caldera.
As a result of the volcano's eruptive history, the islands existed as single landmass from 2015 to 2022:
They were merged by a volcanic cone in a VEI 2 volcanic eruption in 2014–2015.
They were separated again by a more explosive eruption in 2022, which also reduced the islands in size.
Its most recent eruption in January 2022 generated a tsunami that reached as far as the coasts of Japan and of the Americas and a volcanic plume that reached 58 km into the mesosphere.
As of May 2022 the eruption is the largest volcanic eruption in the 21st century.
2022 Hunga Tonga–Hunga Haʻapai eruption and tsunami
In December 2021, an eruption began on Hunga Tonga–Hunga Haʻapai.
The eruption reached a very large and powerful climax nearly four weeks later, on 15 January 2022.
In the Volcanic Explosivity Index scale, the eruption was rated at least a VEI-5.
Described by scientists as a "magma hammer", the volcano at its height produced a series of four underwater thrusts, displaced 10 cubic kilometres of rock, ash and sediment.
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