Japan's Kikai Caldera May Be Refilling Magma, Hinting at Links to Indonesia's Lake Toba

The Kikai Caldera, located south of Japan, may be refilling with magma even after its massive eruption approximately 7,300 years ago. This discovery hints at potential connections with Indonesia's Lake Toba, which has also experienced a supervolcanic eruption in its past. The Kikai Caldera's "Kikai-Akahoya" eruption around 7,300 years ago had devastating consequences for southern Japan. The eruption triggered a megatsunami that submerged islands and blanketed most of mainland Japan and even reached South Korea with volcanic ash. Following the eruption, a caldera measuring approximately 20 km by 17 km and a giant underwater lava dome at a depth of about 600 meters were formed. However, the caldera did not become entirely dormant after the eruption. On May 17, 2026, a minor eruption was observed, with gas and ash spewing up to 400 meters high. This indicates that even after a supervolcanic eruption, magma chambers may not empty completely but can be refilled with new magma, leading to renewed activity. A research team led by Akihiro Nagaya has published a study in the journal "Communications Earth & Environment (Nature)" proposing a model of "melt re-injection" into large magma reservoirs after giant caldera eruptions at Kikai Caldera. They suggest that new magma is naturally injected into the magma reservoir located at a shallow depth directly beneath the caldera, which was responsible for the Kikai-Akahoya eruption. This model may represent common characteristics of volcanoes that have experienced giant caldera eruptions. To detect this magma reservoir, the research team employed a novel measurement technique: deep-sea seismic refraction surveys around the caldera. This method utilizes the measurement of seismic wave velocities propagating through rocks to reveal underground structures. This research offers significant implications for the long-term monitoring and understanding of volcanic activity, especially for countries like Indonesia that have supervolcanoes, such as Lake Toba.