Japanese supervolcano found to be rebuilding magma reservoir

Geologists from the renowned Kobe University have discovered that the massive magma reservoir beneath the underwater Kikai caldera south of Japan is gradually refilling, offering new insights into the long-term recovery of supervolcanoes following catastrophic eruptions.

The findings show that the magma chamber responsible for the largest volcanic eruption of the Holocene is once again accumulating molten rock thousands of years after the event, according to an article on the Science Daily platform.

The Kikai caldera erupted around 7,300 years ago with a Volcanic Explosivity Index (VEI) of 7, ejecting an estimated 133 to 183 cubic kilometres of volcanic material into the atmosphere. It remains the most powerful known eruption of the past 10,000 years.

Although researchers, who published their findings in the journal Communications Earth & Environment, have reported intermittent activity around the caldera—including observations of dark underwater lava domes—since 1925, the new study provides the strongest evidence to date that the volcanic system remains active.

To investigate the structure beneath the seafloor, the research team used seismic refraction surveying. Controlled seismic waves generated by air guns were recorded by seafloor seismometers, allowing scientists to analyse how the waves travelled through the Earth's crust.

The survey identified a zone of unusually low seismic wave velocity directly beneath the Kikai volcano, a signature consistent with the presence of a large magma reservoir located at a relatively shallow depth of 2.5 to 6 kilometres below the surface.

At the same time, the researchers stressed that their discovery does not indicate an imminent eruption.

According to the team, the accumulation of magma in such volcanic systems occurs over thousands of years rather than decades, meaning the presence of newly replenished magma should not be interpreted as evidence that another major eruption is approaching.

Nevertheless, the scientists say the finding is significant because it demonstrates that the magma chamber responsible for the Holocene's largest volcanic catastrophe is once again active and storing new material.

The discovery also provides valuable insight into how supervolcanoes "recharge" after massive eruptions, a process that remains poorly understood.

The authors added that the research could improve scientific understanding of other giant caldera systems around the world, including Yellowstone in the United States and Lake Toba in Indonesia, whose magma reservoirs remain difficult to study despite the potential risks they pose to millions of people living nearby.

By Nazrin Sadigova