Melt re-injection into large magma reservoir after giant caldera eruption at Kikai Caldera Volcano

Abstract Melt re-injection after a giant caldera eruption was quantitatively investigated for the Kikai Caldera Volcano in Japan, which erupted 7300 years ago (Kikai-Akahoya eruption). Our seismic refraction survey revealed a low-velocity anomaly directly beneath the Kikai Caldera Volcano, indicating the existence of a large magma reservoir at a shallow depth of 2.5–6 km. The reservoir can be approximated by a trapezoidal shape in this 2D section, with its width being at least the same as the width of the inner caldera, and its melt fraction was estimated as 3–6%, but could be limited to 10% at most. We propose a melt re-injection model in which new melt is re-injected into this large magma reservoir at the shallow depth just beneath the caldera, which is the same magma reservoir for the Kikai-Akahoya eruption. This model may demonstrate a common feature of volcanoes that have experienced a giant caldera eruption.