Volcano Mount Ontake in Japan erupted on 27 September 2014 killing more than 30 people and injuring as many people.
The volcano, which is a popular destination for religious pilgrimages, erupted when many hikers were out enjoying the beautiful start to the weekend and the autumn hiking season.
The eruption led to pouring in of smoke and ash hundreds of meters into the sky. Ash was found on cars as far as 80km away.
The volcano erupted despite showing no indication that it was about to erupt with such force. An official at the volcano division of the meteorological agency said that although there had been a rising number of small earthquakes detected at Ontake since 10 September 2014, the eruption could not have been predicted easily.
There were no other signs of an imminent eruption, such as earth movements or changes on the mountain’s surface.
Geoscience of the Ontake Eruption
Japan is at a triple-plate subduction boundary between the Eurasian continental plate and the Philippine and Pacific oceanic plates.
As the denser oceanic plates dive below the low-density continental plate, water from the saturated sediments lowers the melting point of surrounding rock. That magma feeds a range of volcanoes mirroring the plate boundary.
History of Eruption of Mount Ontake
Last major eruption of Mount Ontake happened during October 1979 to April 1980. Since then the volcano showed no signs of eruption, although a minor phreatic eruption happened in 2007 and an unconfirmed similar eruption in 1991. Phreatic eruptions are steam-driven explosions caused by magma heating groundwater.
The volcano has been placed under a Level 3 alert by Japanese Meteorological Agency. The Level 3 alert warns everyone to stay away. It was put under Level 3 category in 1984 when the volcano had a major landslide which appeared to be triggered by an earthquake independent of volcanic activity, although ash mixed in the sediment likely increased the landslide's mobility.
About Mount Ontake
The mountain is popular with weekend hikers, particularly in September and October when the autumn leaves are at their best. It is a popular site to view autumn foliage.
The mountain is located some 200 km west of Tokyo in between Nagano and Gifu prefectures. Its peak is 3067m high and the mountain is a popular hiking route, dotted with lodges, cabins and well-marked trails.
It is the second tallest volcano in the country second only to Mount Fuji. Mount Ontake is also known as Ontakesan and Kiso-ontake.
Volcanoes erupt periodically in Japan. Japan is one of the world's most seismically active nations. There have been no fatalities since 1991, when 43 people died in a pyroclastic flow, a superheated current of gas and rock, at Mount Unzen in southwestern Japan.