Characteristics of volcanic materials ejected during 2012-2013 explosive events at the Old Crater on Ioto Island, Ogasawara, Japan

Abstract

Ioto is an active volcanic island (8.5 km long in NE-SW and 4.5 km wide) located about 1250 km south of Tokyo. Since early February 2012, small explosive eruptions have repeatedly occurred at the Old Crater (Million Dollar Hole) in the western part of the island (JMA, 2013). Ejected mud materials collected in the vicinity of the crater consist of free crystals (plagioclase, clinopyroxene, olivine, Fe-Ti oxides), relatively fresh volcanic glass, altered volcanic glass, lithic fragment, altered lithic fragment and pyrite aggregate. No juvenile materials existed in the samples, suggesting these explosive events were phreatic eruption (Ikehata and Tamura, 2013).