A new geophysical survey has found that the vast magma chamber beneath Japan’s Kikai Caldera is refilling. Researchers say the long-quiet system is accumulating fresh melt and could become more active in the future.
Scientists from Kobe University and the Japan Agency for Marine-Earth Science and Technology conducted ship-based campaigns. They deployed ocean-bottom seismometers and used an air-gun system to probe the structure beneath the seafloor. This enabled analysis of how seismic pulses traveled through the crust and allowed a detailed subsurface reconstruction.
The geologists identified a large reservoir beneath a lava dome in the caldera. The melt differs chemically from material linked to the caldera’s prehistoric colossal outburst indicating replenishment by new injections rather than remnants from the ancient eruption,according to Science Alert.
An eruption that destroyed a civilization
The Kikai volcano is known for the Akahoya eruption dated to roughly 7,300 years ago, the largest of the Holocene epoch. In the eruption 160 cubic kilometers of material erupted dwarfing modern events. Scientists believe the Akahoya eruption devastated the Jōmon people, who inhabited the area now known as Japan between 14,000 and 300 BCE. The volcano has produced only minor eruptions in recent decades.
In that event, ash fell over much of Japan and parts of the Korean Peninsula. Scorching pyroclastic flows obliterated life within a radius of up to 150 kilometers. The eruption’s scale was about 11 times greater than Alaska’s 1912 Novarupta and 32 times greater than the 1991 Pinatubo eruption in the Philippines.
The volcano has been largely quiescent since that cataclysm, with only modest activity.
Researchers warn that even a modest eruption from the Kikai Caldera today could prove more devastating than the Akahoya event because of the much higher population density around the region.
Fresh magma
Prior investigations indicated a lava dome has been forming within the caldera for roughly the past 3,900 years. The geochemical profile of the current melt suggests newly supplied magma rather than residual material. This supports a model in which fresh injections gradually recharge a shallow chamber after a super-eruption.
The geologists said they intend to sustain long-term monitoring of the buildup with the goal of being able to detect such “pre-convulsive” indicators years, rather than minutes, ahead of an eruption.
The model proposed by the team for how giant caldera systems refill is presented as a framework that could also apply to other massive volcanic centers worldwide, including Yellowstone in the United States and Toba in Indonesia.