The giant calderas are characterized by the rapid release of large amounts of magma, resulting in vast crater landscapes. They are different than smaller and more frequent eruptions, because these eruptions involve a unique process of magma production, storage, release.
Scientists use tomography and other sophisticated seismic imaging techniques to look inside volcanoes to gain a better understanding of volcanism. The advanced techniques used reveal the size, geometry and complexity of magma reserves hidden in the earth. They also help us understand the mechanisms that control large caldera eruptions.
Around 7,300 years back, Japan’s Kikai Caldera Volcano erupted the Kikai Akahoya, which was the largest Holocene volcanic eruption. Scientists at Kobe University discovered its magma is filling up, which means this ancient volcano slowly recharges.
Scientists detected low-velocity anomalies beneath the caldera using seismic surveys. This is a sign that molten rocks are present.
The reservoir is located at a depth of between 2.5-6km, which is surprisingly near the surface.
Japan confirms giant lava dome in Kikai Caldera
Kikai can provide insights on other massive calderas such as Yellowstone, in the U.S.A. and Toba, in Indonesia. Understanding how magma replenishes these volcanoes can help us predict their future behavior.
SEAMA Nobukazu, a geophysicist at Kobe University said: To understand the eruptions of giant calderas, we must first understand how magma accumulates in such huge quantities.
As we know so little, it is difficult to predict the outcome of a supervolcano eruption.
(c) SEAMA Nobukazu
Scientists teamed with JAMSTEC to study the Kikai Caldera Volcano. The scientists used airguns arrays to generate artificial seismic waves and ocean-bottom seismometers in order to listen to the way those waves traveled within Earth’s crust.
Scientists confirmed that there was a large magma rich region under the volcano which erupted 7300 years ago. The reservoir was mapped, and the size and shape of it were determined.
This gave us an idea about how the giant caldera recharges today.
SEAMA Nobukazu, a geophysicist at Kobe University said: It is evident that the magma reservoir is the same as the one used in the previous eruption.
This magma, however, is not a leftover from the massive eruption that occurred 7,300 years earlier. It’s actually newly-injected magma. The fact that the lava dome in the center of the caldera has formed for 3,900 years and the chemical test results show it is not the same material as the old eruption are the evidence.
This means that magma is most likely being injected into the reservoir beneath the lava dome. summarizes Seama. The scientists can now propose a model of how the magma reservoirs beneath caldera volcanoes are refilled.
This magma reinjection model is compatible with the existence large shallow magma reserves beneath giant calderas such as Yellowstone and Toba.” Seama hopes that the findings of his team will help to understand magma cycles after large eruptions.
Then he says: We want to improve the techniques that proved so valuable in this study, to better understand the processes of re-injection.
The ultimate goal of this study is to improve our ability to track the critical indicators for future large eruptions.
Journal Reference
- Melt re-injection into large magma reservoir after giant caldera eruption at Kikai Caldera Volcano, Communications Earth & Environment (2026). DOI: 10.1038/s43247-026-03347-9
