29 Janvier 2018
January 25, 2018
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.
January 24, 2018
Gunma mountain was quiet for 3,000 years before sudden eruption
Kyodo, Staff Report
KUSATSU, GUNMA PREF. – Fresh details emerged Wednesday about the volcanic eruption at Mount Moto-Shirane in Gunma Prefecture and how it caught the Meteorological Agency and volcanic experts unaware, prompting the agency to release a delayed volcanic warning.
Commenting on Tuesday morning’s sudden eruption, Makoto Saito, director of the agency’s volcanology division, told a news conference later in the day that because there had been “no observational data that suggested signs of volcanic activity before the eruption,” raising the volcanic alert level beforehand would have been near impossible.
According to the agency, there had been no volcanic activity at the Kagamiike crater, the apparent site of the eruption, for about 3,000 years until Tuesday. Because of this long period of dormancy, it had not been part of the agency’s 24/7 volcano-monitoring program.
On the other hand, Mount Moto-Shirane’s Yugama crater, located approximately 2 km north of Kagamiike crater, had been under 24-hour surveillance, with volcanic activity being observed as recently as 2011.
Currently, 50 out of 111 active volcanoes nationwide are under constant watch by the agency. The 50 are selected by a team of experts in coordination with the agency, and recent activity is a crucial factor in deciding whether they are continuously monitored, agency official Toshihiro Imataki told The Japan Times.
Even so, craters that are not active are surveyed once a year by mobile observation teams, he added.
Takahiro Yamamoto, chief researcher at the National Institute of Advanced Industrial Science and Technology, said Tuesday’s eruption “happened in a place we didn’t expect. We can’t be sure of what might happen next.”
After analyzing the eruption’s aftermath, including the volcanic ash that blanketed a nearby ski resort, Kenji Nogami, a professor at the Tokyo Institute of Technology, confirmed Wednesday that the event appeared to have been “a typical phreatic eruption,” or a steam-driven explosion caused when water is heated beneath the ground. Such explosions are more difficult to detect beforehand compared to eruptions caused by the explosion of lava.
Nogami said that in order to detect such eruptions, there was a “need to monitor the craters more thoroughly by installing equipment such as seismometers.”
While the number of volcanic earthquakes has fallen significantly since the eruption at 9:59 a.m. Tuesday, the agency warned that the 2,171-meter mountain, which is part of Mount Kusatsu-Shirane, could again erupt, spewing large volcanic rocks, ash deposits and volcanic gases.
On Wednesday, the land ministry sent experts to survey the eruption by helicopter, while local police and firefighters were searching the area to make sure there were no victims left behind. Those operations, however, were later halted after continuing volcanic tremors were detected.
Yasuo Ishizaki, a volcanic geology professor at the University of Toyama, said that although the likelihood of volcanic mud flow, which often accompanies a snowy mountain eruption, occurring at the mountain appears to be low, “if a large-scale eruption accompanying excretion of lava occurs, it would increase the risk.”