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Editorial: Sudden Mt. Kusatsu-Shirane eruption highlights volcanic dangers

One Japanese Self-Defense Force member died and 11 people were injured, including ski resort visitors, following the recent eruption of Mount Motoshirane, part of the Mount Kusatsu-Shirane stratovolcano on the border between Nagano and Gunma prefectures.

There were no warning signs that the eruption could occur, with the threat level remaining at the lowest level of 1 when it struck. The disaster was a stark reminder of the difficultly in predicting volcanic eruptions.

Mount Kusatsu-Shirane is the collective name for Mount Shirane, Mount Motoshirane and Ainomine peak. It is one of 50 volcanoes in Japan that is monitored around the clock by the Japan Meteorological Agency (JMA).

The agency, however, had focused most of its attention on Mount Shirane, as this peak had been active, having seen a phreatic eruption in 1983. Mount Motoshirane, which lies about 2 kilometers south of Mount Shirane, on the other hand, had apparently not erupted for 3,000 years, and there was no monitoring camera on the mountain.

Immediately after the eruption, the Gunma Prefecture town of Kusatsu reported the information to the JMA, but the agency faced difficulties confirming this, and was unable to issue a flash report informing people on the mountain of an eruption.

Officials must take a renewed look at their monitoring and warning system, placing priority on ensuring the safety of people on the mountain. We understand that budgets are limited, but we hope that efforts will be made to boost video monitoring of volcanoes across the Japanese archipelago.

If a larger eruption of Mount Kusatsu-Shinae occurs, then hot ejecta could trigger a snowmelt-type volcanic mudflow. The town of Kusatsu has already produced a hazard map of areas that could be hit by a mudflow, but this is based on an eruption of Mount Shirane alone. Officials should quickly produce a hazard map for Mount Motoshirane as well.

Learning a lesson from the deadly eruption of Mount Ontake in 2014, the Act on Special Measures for Active Volcanoes was revised, and local bodies where 50 volcanoes are constantly monitored were required to form evacuation plans that extended to tourists in those areas. On the whole, however, local bodies have been slow in the formulation of such plans, with Kusatsu yet to formulate one.

The hot spring resort of Kusatsu lies beyond the areas on the alert for falling volcanic rocks, but the town was hit with a stream of inquiries from people with reservations in the area. Providing accurate information on the volcanoes and formulating evacuation plans should help curb damage from harmful rumors.

There are 111 volcanoes in Japan. It is not unthinkable for an emergency situation to occur around any of them in the future. Local bodies and related organizations need to prepare for sudden eruptions and make an effort to boost monitoring systems and formulate evacuation plans.

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