In 23 days, it will be five years since the eruption of Mt. Kusatsu-Shirane in Gunma Prefecture, where one person was killed and 11 injured.


The Japan Meteorological Agency learned from the eruption at a crater that it had not focused on monitoring, and has strengthened its system by reinspecting volcanoes across the country and installing new surveillance cameras.

On the other hand, the method of predicting the occurrence of a "phreatic eruption" has not yet been established, and the issue is how to prepare for sudden eruptions.

Five years ago, on January 23, 2018, Kusatsu-Shirane in Gunma Prefecture erupted at Mt. rice field.



Since the Japan Meteorological Agency had focused its monitoring on the assumption that an eruption would occur near the summit of Mt. Shirane, about 2 kilometers to the north, the occurrence of an eruption could not be detected immediately, and volcanic disaster prevention became an issue. rice field.



For this reason, the Japan Meteorological Agency has investigated the detailed locations where eruptions have occurred within the past 10,000 years for the 50 volcanoes that are monitored 24 hours a day. increased surveillance cameras by March 2020 for seven volcanoes in Kyushu.



On the other hand, the actual situation is that it is difficult to predict the type of eruption called "phreatic eruption" that occurred at Mt.



Research is underway to make predictions based on data on crustal movements and volcanic earthquakes, but no specific method has been established yet, and how to prepare for sudden eruptions remains an issue. I'm here.

Monitoring system Strengthened volcano

Surveillance cameras have been installed at


Mt. Kusatsu-Shirane,


Mt. Atosanupuri in eastern Hokkaido, Mt.


Nikko-Shirane on the border between Tochigi and Gunma, Mt.


Hakone in Kanagawa Prefecture,


and Mt. Tsurumi and Mt. Garandake in Oita Prefecture.


▽Mt. Kuju in Oita Prefecture


▽The 7 volcanoes of Mt.Aso in Kumamoto Prefecture


.

What is a "phreatic eruption"?

A "phreatic eruption" is an eruption in which groundwater is heated by the heat of magma, and steam is generated suddenly, causing sediment and volcanic ash around the crater to spout out.



There are cases where volcanic eruptions occur without clear warning signs, while there are also cases where volcanic earthquakes are observed but do not lead to eruptions, making it difficult to predict when they will occur.



The scale of eruptions tends to be smaller than eruptions in which magma erupts directly.



In the 2014 eruption of Mt. Ontake, where 63 people were killed or missing, and the 2018 eruption of Mt. to "3".

"Phreatic eruption" research advances, but prediction difficult

Research is underway in various places to elucidate the phreatic eruption.



At the time of the 2018 eruption, Associate Professor Akihiko Terada and his colleagues at the Tokyo Institute of Technology analyzed in detail the data observed by a tiltmeter installed several hundred meters below the ground to investigate the underground structure.



As a result, near-upright fissures in the bedrock were confirmed at a depth of around 1 km directly below the crater of Mt. Motoshirane, and it is speculated that these fissures opened, causing hot water to rise, causing a phreatic eruption.



However, further analysis of past data revealed that in May 2011, there was an "attempted eruption" in which hot water rose but did not lead to an eruption.



Accurate prediction of outbreaks is still not possible.



After clarifying the mechanism of the phreatic eruption of Mt. Motoshirane, Associate Professor Terada and his research team hope to continue observations to help predict eruptions.

Expert “Need to be volcanic risk aware”

Experts point out that in order to prevent damage from eruptions, it is necessary to understand that it is difficult to predict phreatic eruptions and to be aware of the ``distance from the volcano''.



Akihiko Terada, an associate professor at the Tokyo Institute of Technology, said, "Mt. Kusatsu-Shirane offers beautiful scenery, alpine plants, and rare insects, but it's also easily accessible by car, and depending on the season, it's possible to get close to the crater by bus. You can usually enjoy the beautiful nature, but once an eruption occurs, there is a risk that your life will be in danger."



On top of that, there are volcanoes like Mt. Hakone and Mt. Fuji that are easy for people to approach near the crater, not only in the Kanto-Koshin region, but also in Tohoku, Kyushu, and other parts of Japan. He points out that it is necessary to always be aware of how to deal with



Associate Professor Terada says, ``As long as it is an active volcano, there is always the risk of it suddenly erupting without warning.



Specifically, in


the event of an eruption, confirm what route you will


take to escape, and confirm where you can temporarily escape to, such as shelters or large rocks


. I want you to take evacuation action without waiting for information from the local government.