Some 7,300 years ago, the eruption of the Kikai supervolcano, the largest of the Holocene, left behind a vast caldera. Today, this giant structure is filling up with magma once again, preparing for a new cataclysmic eruption.
A team from Kobe University and the Japan Agency for Marine-Earth Science and Technology conducted a detailed undersea exploration campaign. Using seismometers and generated seismic waves, they created a precise map of the caldera's depths, offering an unprecedented glimpse into its internal composition.
The Kikai caldera in Japan, largely submarine, is difficult to study, but its underwater location facilitates geophysical surveys.
Credit: Nobukazu Seama
The work, published in
Communications Earth & Environment, confirms the existence of a vast magma-rich basin beneath the site of the ancient eruption. This reservoir has the same size and is located in the same place as the one that fed the previous event, indicating it is indeed the same system.
Contrary to what one might have thought, the present magma is not simply a remnant of the past eruption. Geochemical analyses show that the lava dome that appeared over the last 3,900 years is formed from new magma.
This observation of a reservoir being refilled aligns with those made under other major calderas, such as Yellowstone in the United States or Toba in Indonesia. Understanding these cycles allows for a clearer view of the future activity of these volcanoes, by identifying signals that could herald a potentially globally cataclysmic awakening.
The next steps aim to refine investigation methods to better understand the reinjection processes. The ambition is to improve the monitoring of indicators for gigantic eruptions.
The mapping shows the size and shape of the magma reservoir under Kikai, identified as being the same as during the previous eruption.
Credit: © A. Nagaya et al. (2026), Communications Earth & Environment (DOI 10.1038/s43247-026-03347-9)