Estimation of gas-releasing efficiency of erupting magma from ²²⁶Ra–²²²Rn disequilibrium

Abstract

VOLATILE components of volcanic magma have an important role in its explosive eruption¹. The volatiles may be partially released from the erupting magma into the air, during eruptive events, and the ratio of the released to the original amount may be a possible determinant of the mode of explosive eruption. Direct measurements of these quantities, however, are extremely difficult; fresh ejecta are rarely obtained. The Sakurajima Volcano, Kyushu, Japan, erupted explosively on 30 October 1975, and discharged pumices and ash-like materials, some of which were later accessible. We report here a change in the measured radioactivity of pumice, possibly due to radon release.