Hydrothermal alteration beneath Owakudani area and the 2015 eruption of Hakone volcano

Abstract

We analyzed the cutting samples from Owakudani #52 borehole (470 m drilling depth), located near the 2015 eruption crater. 5 layers are recognized based on lithology and mineralogy. Layer A (< 100m depth) is suffered low temperature acid alterationcharactized by alunite, gypsum and cristobalite, whereas, Layer B (100 - 360 m depth) is characterized by smectite and quartz, Layers C, D and E (> 360 m depth) are characterized by smectite, chlorite, illite and quartz. The materials ejected at 2015 eruption were derived from Layer A.