Last Saturday, the slopes of Mount Ontake (Nagano Prefecture) shook from a powerful explosion, which heralded the beginning of the eruption of one of the "dormant" Japanese volcanoes. A giant poisonous cloud of incandescent ash and gases buried nearby villages and dozens of tourists in a matter of hours.
For the Land of the Rising Sun, volcanic eruptions are a common occurrence. There are more than a hundred of them here. But thanks to a reliable early warning system, in the vast majority of cases, tragic consequences were avoided. In the case of the Ontake volcano, everything happened quite suddenly.
The National Meteorological Agency YAMA announced the cause of the sudden eruption - a phreatic explosion. The essence of this phenomenon lies in the fact that as a result of the rapid heating of groundwater from the hot magma, a giant cloud of steam is formed, which escapes from the crater under tremendous pressure. At the same time, a pyroplastic flow of incandescent ash and stones is formed, which rushing down the slopes of the volcano with great speed leaves no chance of salvation.
Alas, with existing monitoring methods, an eruption of this type is almost impossible to predict, since there are no visible signs of it in the form of bulges and surface deformation characteristic of other types of eruptions.