Hunga Tonga–Hunga Haʻapai (listen (help·info)) 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.

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. As of May 2022 the eruption is the largest volcanic eruption in the 21st century. Hunga Tonga–Hunga Haʻapai 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.