The last two major eruptions were in 1580 AD ± 20 years and about 1030 AD. They were among the largest Holocene eruptions in Papua New Guinea. Both were explosive eruptions with a Volcanic Explosivity Index of at least 5. The 1580 AD ± 20 years eruption produced pyroclastic flows and probably formed its caldera.[3] The ignimbrite deposit from that eruption, which had a VEI of 6, extends 22 kilometres (14 mi) from the caldera to the coast, and its volume is around 10 cubic kilometres (2.4 cu mi).[1]
Caldera lake
Billy Mitchell caldera lake is about 1,013 m above sea level, has total surface area 3 km2 (1.2 sq mi), and the maximum depth approximately 88.3 m. The only fish species in the lake is the eel Anguilla megastoma. [4]
Billy Mitchell lake drains into the Tekan River.[5]