If it is a huge eruption in Kagoshima, Tokushima and Wakayama will also be a big tsunami Expert analysis September 21 1:05

A huge eruption that occurred about 7300 years ago off Kagoshima Prefecture was known to have caused a large-scale pyroclastic flow and tsunami, but if a eruption of the same scale occurred, a huge tsunami would hit only southern Kyushu. Rather, expert analysis revealed that a large tsunami of 4 to 7 meters could be reached on the coasts of Tokushima and Wakayama prefectures about 500 km away from the crater.

Volcanic eruptions can cause tsunamis not only from pyroclastic flows and ash eruptions, but also from collapse of mountain bodies. In December last year, more than 400 people died in a volcanic eruption in Indonesia.

In Japan, a tsunami has occurred in the past due to a volcanic eruption, and a huge eruption of “Kikai Caldera” in the south of the Satsuma Peninsula in Kagoshima Prefecture, about 7300 years ago. It is thought that a huge tsunami of about 30m has been pushed to the coast.

However, the details of the tsunami, such as the overall picture and mechanism, are not known, and the research group of Shinshu University's assistant professor Masaki Yamada is a sand layer that seems to have been carried by the tsunami along the coasts of Oita, Tokushima, and Wakayama. I examined the distribution of and confirmed the spread.

Based on the assumption that a huge eruption occurred in the “Kikai Caldera” with a diameter of about 20 km and the sea floor collapsed in 30 minutes to 1 hour and a half, the simulation was applied to the current topography.

As a result, Oita City reached 4 meters and 30 centimeters, Minami-cho, Tokushima Prefecture more than 500 kilometers away from the crater, 7 meters and 30 centimeters, and 4 meters in Hidaka-cho, Wakayama Prefecture. It was estimated to cover a wide area.

“The research on tsunami caused by eruptions is overwhelmingly less known than earthquake tsunamis, and it is often unknown. There seems to be no danger of a huge eruption immediately, but risk assessment and disaster prevention are considered. I think such data can contribute to the above. "

The results of this research will be presented at an academic conference held in Tokushima City on the 23rd of this month.