The magma reservoir of the largest volcano eruption of the Holocene is refilling. This Kobe University insight on the Kikai caldera in Japan allows us to understand giant caldera volcanoes like Yellowstone or Toba more generally and gets us closer to predicting their behavior, too.
Some volcanoes erupt so violently, ejecting more magma than could cover all of Central Park 12 km deep, that all that’s left is just a wide and rather shallow crater, a so-called “caldera.” Examples of such supervolcanoes are the Yellowstone caldera, the Toba caldera and the mostly underwater Kikai caldera in Japan, which last erupted 7,300 years ago in what was the largest volcano eruption in the current geological epoch, the Holocene. We know that these volcanoes can and do reerupt but we know very little about the processes that lead up to an eruption and are therefore ill-equipped to make predictions. “We must understand how such large quantities of magma can accumulate to understand how giant caldera eruptions occur,” says Kobe University geophysicist SEAMA Nobukazu.
That the Kikai caldera is mostly underwater is, in fact, an advantage to tackle questions like this. Seama explains, “The underwater location allows us to implement systematic, large-scale surveys.” Thus, the Kobe University researcher teamed up with the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) and used airgun arrays that cause artificial seismic pulses together with ocean bottom seismometers that listen to how that seismic wave propagates through the Earth’s crust to understand its condition.
In the journal Communications Earth & Environment , the team now publishes its findings. They found that there is indeed a region that consists to a large degree of magma directly underneath the volcano that erupted 7,300 years ago and characterized the reservoir’s size and shape. Seama says, “Due to its extent and location it is clear that this is in fact the same magma reservoir as in the previous eruption.”
But this magma is likely not a remnant of that eruption. Researchers had become aware that in the center of the caldera a new lava dome has been forming over the past 3,900 years, and chemical analyses showed that the material produced by this and other recent volcanic activity is of a different composition than what was ejected in the last giant eruption. “This means that the magma that is now present in the magma reservoir under the lava dome is likely newly injected magma,” summarizes Seama. This allows the researchers to propose a general model for how magma reservoirs under caldera volcanoes refill.
“This magma re-injection model is consistent with the existence of large shallow magma reservoirs beneath other giant calderas like Yellowstone and Toba,” says Seama, hoping that his team’s findings may contribute to understanding the magma supply cycles following giant eruptions. He concludes, saying: “We want to refine the methods that have proved to be so useful in this study to more deeply understand the re-injection processes. Our ultimate goal is to become better able to monitor the crucial indicators of future giant eruptions.”
This research was funded by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) (The Third Earthquake and Volcano Hazards Observation and Research Program (Earthquake and Volcano Hazard Reduction Research)) and the Japan Society for the Promotion of Science (grant 20H00199). It was conducted in collaboration with researchers from the Japan Agency for Marine-Earth Science and Technology (JAMSTEC).
Kobe University is a national university with roots dating back to the Kobe Higher Commercial School founded in 1902. It is now one of Japan’s leading comprehensive research universities with over 16,000 students and over 1,700 faculty in 11 faculties and schools and 15 graduate schools. Combining the social and natural sciences to cultivate leaders with an interdisciplinary perspective, Kobe University creates knowledge and fosters innovation to address society’s challenges.
Communications Earth & Environment
Experimental study
Not applicable
Melt re-injection into large magma reservoir after giant caldera eruption at Kikai Caldera Volcano
27-Mar-2026