Tongoa and Epi islands once formed part of a larger island called Kuwae. Local folklore tells of a cataclysmic eruption that split this island into two smaller islands with an oval 12 x 6 km caldera in between (but the story tells of an eruption south of Tongoa). Collapse associated with caldera formation may have been as much as 1100 m. Around 32-39 km³ of magma was erupted, making the Kuwae eruption one of the largest in the last 10,000 years.