A submerged volcano off the coast of Japan that erupted 7300 years ago could be preparing to make a comeback. Scientists have discovered evidence of a giant dome of lava in Kikai volcano’s collapsed magma chamber. They believe it contains about 32 cubic km (7,68 cubic miles) of magma and distortions on its surface suggest dome is growing. Currently the dome is around  6,2 miles (10 kilometers) wide and 1’968 feet (600 meters) tall. Scientists tell an eruption could take place without warning and if it does, it could kill as many as 100 million people and trigger a ‘volcanic winter’. The study, conducted by researchers with Kobe Ocean-Bottom Exploration Center (KOBEC) at Kobe University, confirmed that giant lava dome was created after a caldera-forming supereruption 7’300 years ago. That eruption is thought to have wiped out the prehistoric Jomon civilisation in southern Japan. If new lava dome erupts, it could eject huge amounts of debris into atmosphere, potentially blocking out the sun for some areas to trigger a ‘volcanic winter’. It could also cause tsunami that would hit southern Japan and coasts of Taiwan and China, before striking coasts of North and South America. Paper tells such supereruptions are ‘rare but extremely hazardous events, and also have severe global impacts such as ‘volcanic winter’.

‘Many of these super-volcanoes repeat super-eruptions in their multi-million year histories’ report said, adding that scientists hope to be able to use their research in ‘preparation for the next super-eruption’. Lava dome is in a caldera, a cauldron-like depression that forms following the collapse of a volcano into itself, forming a crater. These collapses are usually triggered when a magma reservoir beneath a volcano is emptied as result of a volcanic eruption. Since KOBEC was established in 2015, Center has carried out three survey voyages. Lava dome rises to 600 metres (1’968,5 feet) above seabed and is now only 30,5 metres (100 feet) beneath surface. According to study, outer and inner caldera rim may overlap on Satsuma Iōjima and Takeshima Islands, which belong to southerly Ōsumi Islands Archipelago off southern coast of Japan.


Six samples collected so far from this dome are rhyolites, a type of igneous rock that forms through cooling of magma or lava, suggesting that dome could contain lava. Researchers discovered several intrusions on surface of dome, leading them to believe that lava is building up underneath dome. They also spotted active gas bubbling, as well as super-heated water columns, near caldera. Professor Yoshiyuki Tastsumi, head of KOBEC and a magma specialist, as well as first author of study, tsaid to newspaper that ‘Although the probability of a gigantic caldera eruption hitting the Japanese archipelago is 1% in next 100 years, it is estimated that the death toll could rise to approximately 100 million in the worst case scenario.’

Researchers equipped training ship Fukae Maru, part of Kobe University Graduate School of Maritime Sciences, with latest observation equipment to survey Kikai Caldera. During 3 voyages, KOBEC carried out detailed underwater geological surveys, seismic reflection (estimating properties of Earth’s subsurface from reflected seismic waves), observations by underwater robots, samples and analysis of rocks and observations using underwater seismographs and electromagneto meters. In their upcoming March 2018 voyage, researchers plan to use seismic reflection and underwater robots to clarify the formation process of caldera revealed in previous surveys and mechanism that causes a giant caldera eruption.

They will also use seismic and electromagentic methods to determine existence of a giant magma build-up and in collaboration with Japan Agency for Marine-Earth Science and Technology will carry out a large-scale underground survey, attempting to capture high-resolution visualizations of magma system within Earth’s crust. Based on results from these surveys, team plans to continue monitoring and aims to pioneer a method for predicting giant caldera-forming eruptions. Japan sits atop 4 different tectonic plates, making it one of Earth’s most seismically active regions. Japan and its islands lie within the Pacific ‘Ring of Fire,’ a horseshoe-shaped geological zone that is a hot bed for tectonic and volcanic activity.

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