*The contents may be subject to change without prior notice.

K. Z. Nanjo¹⁾ and M. Yoshimoto²⁾

1) NaDiR, Global Center for Asian and Regional Research, University of Shizuoka

2) Mount Fuji Research Institute, Yamanashi Prefectural Government

This section explores what a future eruption of Mt. Fuji might be like based on the records of past eruptions. Mt. Fuji is known to have craters aligned along fissures, called fissure craters (Fig. 2-8). Generally, they are aligned northwest to southeast, which is because of tectonic plate movements. The Izu Block drifting from the south collided with Honshu and pushed an area around Mt. Fuji. As this area is located northwest of the Izu Peninsula, there is relatively strong compressive force in the northwest-southeast direction. Perpendicular to this direction, a tensile force is generated, creating cracks which open in the northeast-southwest direction along the northwest-southeast line. These cracks allow lava to flow out, and eventually develop into fissure craters. The hazard map of Mt. Fuji shows the locations where it is thought that craters would form based on the distribution of past craters.

The analysis of past fissure eruptions revealed that the distance from the summit to the farthest crater was about 13.5 kilometers. Taking into consideration all possible uncertainties, we can reasonably conclude that in a future eruption of Mt. Fuji, craters are likely to form within a diameter of approximately 27 kilometers from the summit.

Past eruptions of Mt. Fuji occurred on varying scales. While the Hoei and Jogan Eruptions were relatively large, most other eruptions were about one tenth in size. For this reason, some argue that disaster risk management should focus on small-scale eruptions that occur more frequently.

On the other hand, data on volcanic eruptions around the world show that volcanoes that have remained dormant for several centuries are likely to cause a large eruption. Considering that more than 300 years have passed since the 1707 Hoei Eruption, Mt. Fuji could erupt on a large scale in the near future. If we can forecast the scale of an eruption beforehand, we can better prepare for a future disaster, but the current level of science allows us to identify the scale of an eruption only afterward, which makes disaster management difficult.

When an eruption occurs at Mt. Fuji, the first response must be to flee. It is also important to decide in advance where to meet up with your family members after the eruption subsides.

Fig. 2-8: Distribution of craters on Mt. Fuji.

(Left) At Mt. Fuji, many eruptions occurred at fissure craters not only at the summit but also on the slopes. The white circle shows the zone of 13.5-kilometer radius around the summit.

(Right) Image showing directions of forces.