The eruption of Mount Ontake has caused 30 probably deaths. However, more than 200 hikers taken by surprise managed to escape, and one of them has even provided a video of what it is like to be overtaken by a volcanic ash cloud.
Mt. Ontake is a popular tourist spot, lying 200 kilometers from Tokyo and containing five beautiful crater lakes. It is the second highest volcano in Japan and its gently sloping sides make for reasonably easy walking. Although there were minor eruptions in 1991 and 2007, the largest one happened in 1979.
The timing of the eruption was particularly tragic—just before midday on a Saturday when it's prime time for visitors, and with no significant earthquake warnings.
The eruption has been described as a hydrovolcanic explosion by geologists who attributed it to ground water being heated to the point where it rapidly turned to steam, driving ash and gasses as much as three kilometers from the crater.
Article taken from http://www.iflscience.com/