Mineralogical Aspects of Volcanic Eruption

Abstract

Phase and compositional variations in minerals have been investigated in the light of change of the physical conditions of magma during eruption. Significant role of water vapor pressure as well as temperature is demonstrated in the explosive activity of the “Futatsu-dake eruption” ; possible increase of the water vapor pressure before eruption is suggested by the reversed zoning of hypersthene and hornblende, and sudden decrease of it after the eruption is correlated with cease of hornblende crystallization and beginning of sector-zoned augite. Effect of undercooling of magma due to the volatile release is stressed. Temperature and oxygen pressure change and possible reduction of magma during eruption are well reflected by Fe-Ti oxide minerals.