Two large-amplitude volcanic earthquakes struck beneath Mount Tokachi in Hokkaido on September 12, bringing the count of such quakes over 30 days to five, and by 9:30 that morning the Japan Meteorological Agency had raised the volcano’s alert from Level 2 to Level 3. Hikers were barred from both trailheads on the mountain and a 3-kilometre no-entry ring was drawn around its active crater.
The restriction landed on one of the most visited peaks in Daisetsuzan National Park, and it followed six months of slow, measurable change in the ground and gas output of the mountain rather than a single sudden event.
Five big quakes in a month and a mountain that had been swelling since March
The Smithsonian and USGS Weekly Volcanic Activity Report for September 17-23 lays out the sequence as the Japan Meteorological Agency, or JMA, reported it. Instruments detected inflation at relatively shallow depths beginning in March. Gas emissions rose from April, with more frequent diffuse venting and crater glow visible on cameras. Plumes became common by May, and then the volcano produced very small eruptions near its 62-2 crater on July 22, August 5 and August 6. The two big quakes on September 12 were the fourth and fifth of the past 30 days, and the report ties the alert change directly to them.
A trade-press account of the announcement adds that larger volcanic earthquakes had been increasing noticeably since August 17, with the strongest arriving around 8:20 a.m. on the day of the raise, barely an hour before the agency acted.
The July 22 eruption drew particular notice because it broke a long quiet spell. The trade report describes it as the first eruption in 22 years, which lines up with the 2004 episode that reference listings give as the mountain’s last notable activity. Three small eruptions inside about two weeks, all near the same crater, is the pattern that moved the JMA from watching to restricting.
Which trails and roads closed
According to the account published on September 12, climbing is prohibited from both the Tokachidake Onsen and Fukiage trailheads, the two starting points for routes toward the Daisetsuzan range. The Tokachidake Skyline road is closed between Biei Shirogane Onsen and Tokachidake Onsen. The Fukiage Onsen Health Center Hakuginso and the Fukiage Roten-no-Yu open-air bath closed until further notice, though certain lodgings kept limited operations.
The principal restricted area reaches about 3 kilometres from the 62-2 crater. The agency’s stated worry is physical and short-ranged: large volcanic rocks thrown from the crater during an eruption, plus ash and smaller projectiles that could travel beyond the ring. A separate trade report says local authorities issued evacuation orders for the Fukiage Onsen area and advised vulnerable residents at Tokachidake Onsen to leave, while the same reporting on the raise notes that the town centres of Furano and Biei were not placed under evacuation orders.
What Level 3 does and does not authorise
History explains why the agency draws the line where it does. The same trade report recalls that an eruption in 1926 sent a large mudflow down the mountain and left 144 people dead or missing, and it points to the 62-2 crater, named for a 1962 eruption, as the current focus of concern. A 3-kilometre ring around that crater is what the current restriction is built on.
Japan’s five-step alert scale is built around who is allowed where. In the JMA’s own explanation of the alert levels, near-crater warnings go to non-residential areas near the crater when the level is 3, and to the wider crater surroundings at Level 2. Level 3 therefore closes the mountain to entry without ordering town evacuations, which is the posture Furano and Biei are in.
The mountain itself is large. Reference listings put the summit at 2,077 metres, the tallest peak of the Tokachi Volcanic Group, with four hiking routes to the top, a hut, a campground and a hot spring. Its most recent notable activity before this year is dated to February through April 2004, and the Sapporo District Meteorological Observatory is the office that made the September 12 decision.
What could change the picture
An alert level describes the state of the ground and the range of danger, and it carries no timetable for an eruption. The agency’s live page for the mountain still showed Level 3 on a bulletin dated September 28, sixteen days after the raise, with no change recorded.
Nobody can yet say whether the shallow inflation that began in March keeps feeding the quakes. Nothing in the September report says the swelling has stopped, and a sixth large quake or a fourth small eruption would put the agency back in front of the same decision that closed the trails on September 12.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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