Japan's Kikai supervolcano is actively refilling with fresh magma, study finds

Saturday 28 March 2026 - 10:50

By: Dakir Madiha

Japan's Kikai supervolcano is actively refilling with fresh magma, study finds

The magma reservoir beneath Japan's Kikai caldera, site of the largest volcanic eruption of the Holocene epoch, is actively recharging with fresh molten rock, according to new research published March 27 in the journal Communications Earth & Environment. The findings provide the first detailed picture of how supervolcanoes replenish themselves between catastrophic eruptions, with implications for monitoring similar systems worldwide, including Yellowstone and Toba.

A team led by geophysicist Seama Nobukazu of Kobe University, working alongside the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), deployed air gun arrays and seafloor seismometers to map the subsurface of the largely submerged caldera off southern Japan. They identified a large, magma-rich zone at shallow depths, between 2.5 and 6 kilometers, located directly beneath a lava dome that has been growing at the caldera's center for 3,900 years.

The size and position of the reservoir led researchers to conclude it occupies the same space that fed the caldera-forming eruption 7,300 years ago. "Due to its extent and location, it is clear that this is indeed the same magmatic reservoir as during the previous eruption," Seama said. However, chemical analysis of lava dome material shows it differs from what was ejected during the ancient explosion, indicating the current magma is not a remnant. "This means the magma currently present in the magmatic reservoir beneath the lava dome is likely newly injected magma," he added.

The team estimates the reservoir's volume at roughly 220 cubic kilometers, with at least 32 cubic kilometers of molten material injected over the past 3,900 years, averaging more than 8.2 cubic kilometers per thousand years.

The team also proposed a broader model of magma reinjection, describing how volcanic calderas replenish their magma supplies after giant eruptions, a process that had remained poorly understood. Seama noted the model "is consistent with the existence of large shallow magmatic reservoirs beneath other giant calderas such as Yellowstone and Toba." Similar depth overlaps between current reservoirs and past eruption estimates have been observed at Yellowstone, where magma sits between 3 and 8 kilometers deep.

The underwater location of Kikai's caldera proved an asset, enabling systematic seismic surveys that would be difficult to conduct on land. "Our ultimate goal is to improve our ability to monitor crucial indicators of future giant eruptions," Seama said.