A submerged volcano off the coast of Japan – which last erupted 7,300 years ago – is ‘preparing to erupt’ again, scientists say.
Scientists have reportedly discovered evidence of a ‘giant dome of lava’ in the Kikai volcano’s magma chamber and they warn it could kill as many as 100 million people.
They said an eruption could take place without warning and if it does erupt, it could trigger a ‘volcanic winter’.
It’s believed to contain around 32 cubic km (7.68 cubic miles) of magma and they’ve found distortions on its surface which suggest the dome is growing – currently it’s around 6.2 miles (10 kilometers) wide and 1,968 feet (600 meters) tall.
The study, conducted by researchers with the Kobe Ocean-Bottom Exploration Center (KOBEC) at Kobe University, said the giant lava dome was created after a ‘caldera-forming supereruption’ 7,300 years ago.
The eruption is thought to have wiped out the prehistoric Jomon civilisation in southern Japan.
If the new lava dome erupts, it could eject huge amounts of debris into the atmosphere, potentially blocking out the sun for some areas, triggering a ‘volcanic winter’.
It could also cause a tsunami which would hit southern Japan and the coasts of Taiwan and China, before striking the coasts of North and South America.
The paper says such super-eruptions are ‘rare but extremely hazardous events, and also have severe global impacts such as ‘volcanic winter’.
The report reads:
Many of these super-volcanoes repeat super-eruptions in their multi-million year histories.
The lava dome is in a caldera – which is a ‘cauldron-like depression’ which forms following the collapse of a volcano into itself, creating a crater.
These collapses are usually triggered when a magma reservoir beneath a volcano is emptied as the result of a volcanic eruption and the lava dome is now only 30.5 metres (100 feet) beneath the surface.
According to the study, the outer and inner caldera rim may overlap on Satsuma Iōjima and Takeshima Islands, which belong to the southerly Ōsumi Islands, Archipelago, off the southern coast of Japan.
Six samples collected so far from this dome are rhyolites – a type of igneous rock which forms through the cooling of magma or lava – suggesting the dome could contain lava.
The researchers discovered several intrusions on the surface of the dome, leading them to believe lava is building up underneath the dome.
They also spotted active gas bubbling, as well as super-heated water columns near the caldera.
Professor Yoshiyuki Tastsumi, head of KOBEC and a magma specialist, told The Mainichi:
Although the probability of a gigantic caldera eruption hitting the Japanese archipelago is one per cent in the next 100 years, it’s estimated the death toll could rise to approximately 100 million in the worst case scenario.
Researchers equipped training ship Fukae Maru, part of the Kobe University Graduate School of Maritime Sciences, with the latest observation equipment to survey the Kikai Caldera.
During the three voyages, KOBEC carried out detailed underwater geological surveys, seismic reflection (estimating the properties of the Earth’s subsurface from reflected seismic waves), observations by underwater robots, samples and analysis of rocks, as well as observations using underwater seismographs and electromagnetometers.
In their upcoming March 2018 voyage, the researchers plan to use seismic reflection and underwater robots to clarify the formation process of the caldera revealed in previous surveys and the mechanism which causes a giant caldera eruption.