The Kikai Caldera, a massive submarine volcano off southern Japan that produced the most destructive eruption on Earth in the past 10,000 years, is showing signs of entering a new phase of activity. Scientists are paying close attention after detecting evidence that magma is steadily re-accumulating directly beneath the site of the ancient mega-eruption.
Surveying 175 Km of Seafloor: "We Must Understand the Mechanism Behind Giant Eruptions"
A research team at Kobe University in Japan published findings in the international journal *Communications Earth & Environment* analyzing that magma is gradually building up again beneath the Kikai Caldera, located near Io Island in the Ryukyu Islands chain off Kagoshima Prefecture.
The caldera expelled approximately 160 cubic kilometers of volcanic material in a single eruption roughly 7,300 years ago. For comparison, the 1980 eruption of Mount St. Helens in the United States released less than 1 cubic kilometer, and the 1991 eruption of Mount Pinatubo in the Philippines produced only about 10 cubic kilometers.
In the approximately 3,900 years following that eruption, magma pushed up through the caldera floor and formed the world's largest lava dome, measuring 32 cubic kilometers.
Nobukazu Seama, the geophysicist who led the research, stressed that "to understand how giant caldera eruptions occur, we first need to understand how such enormous volumes of magma accumulate."
The team partnered with the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) and deployed 39 underwater sensors across a 175-kilometer transect spanning the caldera.
They then used ship-mounted air guns to send sound waves into the seafloor and analyzed more than 12,000 wave recordings. The effort successfully produced a three-dimensional image of the subsurface structure beneath the seafloor.
Newly Introduced Magma Accumulating at Over 8.2 Cubic Km per 1,000 Years
The analysis revealed a striking finding. The magma reservoir that fueled the ancient mega-eruption remains in an active state thousands of years later.
The chemical composition of magma within the lava dome also differed markedly from past eruptive material. Seama added that "this suggests the magma currently present in the reservoir beneath the lava dome is likely newly recharged magma."
The researchers estimate that more than 8.2 cubic kilometers of new magma has flowed in on average every 1,000 years.
"The process of melt re-injection into the shallow magma reservoir directly beneath the caldera could represent a stage leading to a future giant caldera eruption," the paper stated.
The magma recharging pattern at the Kikai Caldera mirrors patterns observed in large shallow magma systems at Yellowstone in the United States and Lake Toba in Indonesia.
The researchers suggested that if this phenomenon is a process common to giant caldera volcanoes, the detection techniques used in this study could be widely applied to eruption-prediction monitoring.
Current technology cannot determine how much more magma must accumulate before a large-scale eruption is triggered. However, given that a volcano with one of the largest eruption records on Earth has been quietly storing energy for 7,300 years, calls for establishing a long-term monitoring system are gaining urgency.