Researchers from Kobe University have discovered that a vast reservoir of magma beneath Japan’s Kikai caldera is actively refilling, providing a rare opportunity to study how some of the world’s largest volcanic systems recover after catastrophic events. The findings, published in Communications Earth & Environment, suggest that new molten material has entered the system over time rather than simply remaining from previous activity.
Mapping the Magma Reservoir
Kikai is a mostly submerged volcanic caldera located south of Japan. Approximately 7,300 years ago, it produced the largest known volcanic eruption of the Holocene epoch. During that event, roughly 36 cubic miles of rock spread across about 1,700 square miles, with pyroclastic flows traveling up to 93 miles from the volcano. This eruption is believed to have wiped out the prehistoric Jomon civilization in southern Japan.
To study the current state of the volcano, Kobe University geophysicist Discovermagazine and his team utilized the caldera’s underwater location to conduct systematic, large-scale surveys. Working with the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), the researchers used airgun arrays to generate controlled seismic waves and ocean bottom seismometers to track those waves as they traveled through the crust.
The data revealed a substantial magma-rich region directly beneath the area responsible for the eruption 7,300 years ago. The reservoir is estimated to be located approximately 1.5 to 3 miles below the surface, a depth similar to where magma sat before the last giant eruption. According to Seama, the reservoir’s extent and location make it clear that it is the same system that supplied magma for the ancient disaster.
Evidence of Magma Re-injection
While the reservoir is the same, the magma within it appears to be new. Scientists have observed a lava dome forming near the center of the Kikai caldera for approximately 3,900 years. Chemical analyses indicate that this newer material differs from the magma expelled during the eruption 7,300 years ago, suggesting a process of magma re-injection.
Seama noted that this re-injection model is consistent with the existence of large, shallow magma reservoirs found beneath other giant calderas, such as Toba in Indonesia and Yellowstone in the United States. The scale of these systems is immense; researchers note that the volume of magma involved in such eruptions could cover all of Central Park to a depth of 12 kilometers (roughly seven miles).
Predicting Future Super-Eruptions
The discovery is intended to help scientists better distinguish ordinary volcanic activity from the indicators of a much larger event. Seama stated, We must understand how such large quantities of magma can accumulate to understand how giant caldera eruptions occur
, adding that the ultimate goal is to monitor the crucial indicators of future giant eruptions.
The potential stakes of a future Kikai eruption are significant. The volcano is situated within the Ring of Fire, where tectonic plates slide under one another. Potential risks include:
- Atmospheric Impact: An eruption could throw debris into the atmosphere, blocking sunlight and creating a “volcanic winter” with cooler temperatures.
- Tsunami Risk: A major event could trigger tsunamis affecting China, Taiwan, southern Japan, and the Americas.
- Human Cost: Yoshiyuki Tatsumi warned that in a worst-case scenario, deaths could reach approximately 100 million, though he estimated the chance of such an eruption occurring within the next 100 years is about 1 percent.
Current activity at the site includes more than a dozen small earthquakes in recent years and reports of steam emerging from the crater.
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