Tofua Arc at 20.9°S Volcano — Tonga

An unnamed submarine volcano is located along the Tofua Volcanic Arc 35 km NW of the Niu Aunofo lighthouse on Tongatapu Island. The first documented eruptions took place in 1911 and 1923; an ephemeral island was formed in 1999. A submarine eruption in January 2017 produced discolored water visible in satellite imagery.