Long Island, located 136 km east of Madang in the Vitiaz Strait, consists of 2 adjacent partly collapsed steep-sided stratovolcanoes: Mount Reaumur in the north and Cerisy Peak in the south.
The central part of the complex contains a large 10x12.5 km caldera filled by a lake, Lake Wilson. The youngest eruptions have built a new cone inside the south-central part of the caldera lake, Motmot Island, which formed in 1953-54 and 1968. The historic eruptions in the 20th century occurred from vents at or near Motmot Island.
Long Island volcano's eruptions are often strombolian and sometimes submarine.
Collapse of the basaltic-andesitic volcanic complex produced a large 10 x 12.5 km caldera, now filled by Lake Wisdom. Caldera formation occurred during at least 3 major explosive eruptions, about 16,000, 4000, and 300 years ago. The latter was one of the largest historical eruptions in Papua New Guinea and deposited andesitic tephra across the New Guinea highlands, prompting legends of a "Time of Darkness."
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