Nobuo Uchida

"This paper is a non-peer reviewed preprint submitted to EarthArXiv"
For humans living in an economic zone adjacent to volcanoes, the reality of unpredictable eruptions is a constant concern. This paper presents a new view on the phreatic eruption process of Mt. Ontake, Japan. The purpose of this posting is to find ways to reduce casualties from phreatic eruptions. As a background, there is the current situation that phreatic eruptions where magma does not move cannot be predicted. By analyzing the process of phreatic eruptions in which the magma does not move, future eruption prediction measures will be established. The significance of the submission is that this research is shared not only by researchers in Japan but also by researchers around the world. It is highly likely that the water necessary for the phreatic eruption was supplied by accidental heavy rains in addition to the water stored in the mountain. On the other hand, it is presumed that the lava rock surrounding the magma cooled from the outside over a long period of time. As the cooling water from heavy rain hit the heated lava rocks continuously, the lava rocks were gradually scraped away while the vaporization phenomenon continued, colliding with the hotter lava rocks and leading to a large explosion. At this time, the power of the explosion was not able to pass through the escape route, and it became a large eruption that reached the top of the mountain. The event occurred 7 minutes after it was first observed by the seismometer. As a result, it was not possible to predict the eruption, resulting in casualties.