Japan's Giant Caldera Volcano is Refilling 7,300 Years Later

March 27, 2026
by Kobe University

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The magma reservoir associated with the largest volcanic eruption of the Holocene epoch is currently undergoing a refill. Recent insights from Kobe University regarding the Kikai caldera in Japan contribute to our understanding of supervolcanoes, including notable examples like Yellowstone and Toba, while simultaneously improving our predictive capabilities concerning their behavior.

Supervolcanoes have the potential to erupt with calamitous intensity, resulting in vast craters referred to as "calderas." The Kikai caldera, which last erupted approximately 7,300 years ago, is recognized as the most significant volcanic event in the Holocene era. While it is known that these calderas can initiate further eruptions, the precursory processes leading to such events remain poorly understood, posing challenges for accurate predictions.

According to Seama Nobukazu, a geophysicist at Kobe University, it is vital to comprehend the mechanisms behind the accumulation of large amounts of magma to facilitate predictions of caldera eruptions.

The primarily submerged location of the Kikai caldera provides distinct advantages for conducting research. Seama elaborates, "The underwater environment allows us to implement systematic, large-scale surveys."

In partnership with the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), the research team employed airgun arrays to produce artificial seismic pulses, complemented by ocean bottom seismometers to examine the propagation of seismic waves through the Earth's crust, thereby assessing its structural conditions.

The results of their investigation, published in the journal Communications Earth & Environment, reveal a substantial presence of magma beneath the volcano, characterized by distinct size and shape. Seama indicates that this reservoir is likely associated with the conditions present during the previous major eruption.

Further research suggests that the magma found in the caldera is not simply leftover from the previous eruption. Instead, a new lava dome has been forming in the caldera's center over the past 3,900 years, indicating that the current material composition differs from that expelled during the last major eruption.

Seama summarizes the implications: "This means that the magma reservoir beneath the lava dome is likely comprised of newly injected magma," which leads to the proposal of a general model for the refilling of magma reservoirs beneath caldera volcanoes.

The research team's aim is for their magma re-injection model to be applicable to other giant calderas such as Yellowstone and Toba, thus enhancing our comprehension of magma supply cycles following eruptions.

In conclusion, Seama underscores, "We intend to refine our methods to gain a deeper understanding of the re-injection processes, ultimately improving our monitoring of indicators that signal potential future giant eruptions."