About: Niuatahi

Niuatahi, also known as Volcano O or MTJ-1, is a nearly circular submarine caldera in the Tonga Islands of the South Pacific Ocean. The volcano is 15 km (9.3 mi) across, and rises 1,340 m (4,400 ft) above the seafloor. The caldera is 9 km (5.6 mi) wide. The caldera floor lies about 2 km (1.2 mi) under the ocean, although a 730 m (2,400 ft) high volcanic cone inside the caldera named Motutahi rises to 1,270 m (4,170 ft) below sea level. The volcano is surrounded by lava flows extending 60 km (37 mi) from the caldera. Dacite is the primary volcanic rock composing Motutahi and the surrounding caldera floor. Hydrothermal venting takes place adjacent to the inner caldera walls and on the summit of Motutahi.