Scientists have discovered that the magma chamber associated with the largest volcanic eruption of the Holocene is filling up again. The discovery, led by Kobe University researchers studying Japan’s Kikai caldera, provides new insights into how large caldera systems such as Yellowstone and Toba evolve over time, and could help improve predictions of future eruptions.
Some volcanic eruptions are so extreme that they release enough magma to bury the entirety of Central Park within a 7-mile radius. After such an event, the landscape collapses into a wide, relatively shallow crater known as a caldera. Famous examples include Yellowstone in the United States, Toba in Indonesia, and the largely submerged Kikai Caldera in Japan. Mount Kikai last erupted 7,300 years ago during the Holocene, the most powerful eruption of the current geological era. Scientists know that these systems can erupt again, but the accumulation of such events is not yet fully understood. “To understand how giant caldera eruptions occur, we need to understand how such large amounts of magma accumulate,” says Nobukazu Sema, a geophysicist at Kobe University.
Underwater seismic images reveal magma system
Kikai’s underwater environment offers unique advantages for research. “Because it’s underwater, we can conduct systematic, large-scale surveys,” Seema explains. Working with the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), the team used air gun arrays to generate controlled seismic pulses and used submarine seismometers to track how those waves traveled through the Earth’s crust. This approach allowed us to build a detailed image of the structure beneath the caldera.
The result is Communication Earth and Environmenta large magma-rich zone has been identified directly beneath the ancient eruption site. Researchers were able to map the size and shape of the reservoir and identify connections to past activity. “It’s clear from its extent and location that this is indeed the same magma chamber from the previous eruption,” Seema said.
Injection of fresh magma accelerates the recharging process
The magma currently present does not appear to be a remnant of a previous eruption. Scientists had already observed a lava dome forming in the center of the caldera over the past 3,900 years. Chemical analysis showed that this new material was different from the material released during previous eruptions. “This means that the magma currently present in the magma chamber beneath the lava dome is likely newly injected magma,” Seema summarizes. These findings support a broader model that explains how magma chambers beneath caldera volcanoes replenish over time.
Implications for Yellowstone and future eruptions
The proposed magma reinjection model is consistent with observations of large, shallow magmatic systems underlying other major calderas such as Yellowstone and Toba. Seema suggests this research could help scientists better understand how the magma supply cycle unfolds after large eruptions. “We hope to refine the techniques that proved so useful in this study to better understand the reinjection process. Our ultimate goal is to be able to better monitor important indicators of future mega-eruptions,” he concluded.
This research was supported by the Ministry of Education, Culture, Sports, Science and Technology (3rd Earthquake and Volcanic Disaster Observation Research Project (Earthquake and Volcanic Disaster Mitigation Research)) and the Japan Society for the Promotion of Science (Grant-in-Aid for Scientific Research 20H00199). This was carried out in collaboration with researchers from the Japan Agency for Marine-Earth Science and Technology (JAMSTEC).
