Explosive eruption history and development of hydrothermal system at Chokai volcano during the last 3,000 years

Abstract

Every 100 years, Chokai erupts explosively, according to our observation on the only outcrop at where the sequence of fallout layers is well preserved. Scoriaceous ash is accompanied by hydrothermally altered lithics in varying degrees, indicating that the eruption type ranges from volcanic-hydrothermal to magmatic (strombolian and vulcanian) eruptions. Chemical variations of altered ash grains imply that the hydrothermal system involves silicic and advanced argillic alteration zones. The hydrothermal system interacts with ascending magma in each eruption.