A model for crustal deformations associated with the 1914 great eruption of Sakurajima volcano, Kagoshima, Japan

Abstract

Sakurajima volcano, which is located on the southern rim of the Aira caldera, Kagoshima, is one of the most active volcanoes in Japan. The 1914 eruption of Sakurajima volcano was accompanied by an intensive fissure eruption and caused significant crustal deformations. The north side of the newly formed fissure craters, which are arranged in the WNW-ESE direction, moved toward the north by about 5 m, and the south side moved toward the south by 3 m. Furthermore, the ground surface around the Aira caldera was concentrically depressed by 80 cm. In order to explain these significant crustal deformations, a model consisting of a tensile fault and a deflation source is presented. By means of the least-squares fitting of the model to leveling data around the Aira caldera, we obtained the parameters of the deflation source as follows: depth 8.8 ± 1.2 km; subsidence just above the source 157 ± 27 cm. The source is located at the center of the Aira caldera. On the other hand, the tensile fault, which corresponds to the fissure craters, is estimated, on the basis of horizontal movements in Sakurajima, to be 7 km long, 1.5 km wide and 0.5 km deep at its upper margin, with an opening of 20 m. This model suggests that magma flowed out of the reservoir beneath the Aira caldera and broke the crust of Sakurajima, thus creating fissure.