Hunga Tonga Hunga Ha'apai

Hunga Tonga-Hunga Ha' apai is a submarine volcano in the South Pacific located about 30 km (19 mi) south of the submarine volcano of Fonuafoʻou and 65 km (40 mi) north of Tongatapu, Tonga's main island. 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 (62 mi) above a very active seismic zone.
The volcano rises around 2,000 m from the seafloor and has a caldera which — in the eve to 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 Ha'apai, 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,and 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 (36 mi) into the mesosphere. Preliminary data indicates that the event was probably the largest volcanic eruption in the world since the 1991 eruption of Mount Pinatubo. Hunga Tonga–Hunga Ha'apai likely had a previous major explosive eruption in the late 11th or early 12th century (possibly in 1108). Several known historical eruptions occurred in 1912, 1937, 1988, 2009, 2014–15, and 2021–22.