In August 2012, scientists conducted an intensive geological survey of the submarine rhyolitic Omurodashi volcano located south of Izu-Oshima, Tokyo Metropolis, using the remotely operated vehicle (ROV) Hyper Dolphin.
The survey, led by Kenichiro Tani, Research Scientist, Institute for Research on Earth Evolution (IFREE) Japan Agency for Marine-Earth Science and Technology (JAMSTEC), is the first to discover that this volcano is currently active. The evidence for this is provided by a zone of continuous submarine hydrothermal activity in the crater-like depression (Omura hole) at the center of the volcano. Hydrothermal deposits generated by this activity, including chimneys of metal sulfides that built up around the hydrothermal vents, were successfully collected during the survey.
This discovery has important implications. Researchers will have to assess the risks and hazards posed by the possible eruption of the shallow-water rhyolitic Omuradashi volcano, and the value of the ore deposits formed in the hydrothermal zone. The interaction between rhyolitic lava and seawater during an eruption in the shallow waters of Omurodashi has the potential to cause explosive eruptions. These will have an impact upon waters surrounding the eruption site, and may be powerful enough to affect neighboring coastal areas. Further investigations are thus essential to clarify the eruptive history and evolution of Omurodashi volcano in order to assess the risks and hazards posed by any future eruptions.
The discovery of this active volcano and the results of this first survey were presented at the fall FY 2012 meeting of The Volcanological Society of Japan held in Miyota, Nagano from October 14.
Press Release, November 15, 2012