As volcanic eruptions have been known to directly impact human life, this topic has been extensively studied within the earth science community. Among the 111 active volcanoes in Japan, 50 have a “24-hour constant observation monitoring system” installed (Fig. 1).
In other words, an observation system consisting of heavy equipment is being put in place. The observation system that was in place during the eruption of Mount Ontake (as shown in Additional file 1) is a system that detects underground movement using a seismograph, as well as GPS and a remote camera.
An Automated Meteorological Data Acquisition System (AMeDAS; Japanese Meteorological Agency)2 is also installed on the top of Mt. Ontake coincidently, but these data are not available in the volcanic observation system. What does this mean?
It seems that people believe that this meteorological observation instrument should be thought of to observe the weather alone and that it is irrelevant for observing volcanic eruptions. In effect, this implies that rainfall is not considered a direct cause of eruptions.
However, when mountains that are not designated as active volcanoes (so-called unlabeled mountains) suddenly erupt, they often create victims. One recent example of this occurred on January 23, 2018, when steam erupted from Mt. Motoshirane, which had been used as a ski resort, killing one person, and injuring 11 people. Because these steam eruptions occurred suddenly and without any warning, they caused a human tragedy for holidaymakers. As human habitations exist near active volcanoes in Japan, it is inevitable that as soon as a volcano erupts, human lives, essential utilities, and daily routines will be negatively impacted.
In this paper, we attempted to analyze the September 27, 2014 phreatic (steam) eruption of Mount Ontake, which took the lives of 58 climbers and 5 missing and presumed dead, who were enjoying lunch at the summit when it suddenly erupted without warning, becoming the worst volcanic disaster in recent years.