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In Matsumoto City, Nagano Prefecture, several massive rocks collapsed and tumbled down a slope, causing damage to houses and roads. When we covered the scene, we found that the nearby forest had been cleared of dead pine trees that had been damaged by pine beetles, leaving a large area of exposed mountainside.
■Destruction of house walls and garage Just before midnight, footage from a security camera installed at a house showed the garage roof suddenly collapsing with a deafening noise. Another camera installed elsewhere captured footage of a massive rock tumbling down at high speed. The rockfall occurred late at night on the 7th in Matsumoto City, Nagano Prefecture. Three rocks fell, but there were no injuries. Even on the 12th, the rocks were still at the site. The asphalt that the rocks passed over was dented, and the wall of the house that was directly hit was shattered into pieces. The rocks fell from the mountain behind the house. We spoke to the mountain owner (in his 70s). “There was a small stream, and the rocks were rolling down along the stream, and I jumped and hit the garage on the first, second, and third jumps.” “(Q. So you ended up there?) That’s right, I went in there.” “I’ve never seen such large rocks fall since I was old enough to remember. It was the first time. It was really scary.”
■Forest logging due to pine beetle damage The program was given permission to enter the mountain. We climbed a fairly steep slope to the place where the rocks were thought to have been. At the site, there were rows of trees that had been cut down artificially. Looking from below, it was clear that there were multiple places where a large number of Japanese red pines had been cut down. Mountain owner: “It’s my mountain, but the prefecture manages it. They don’t decide whether it’s okay to cut down trees or not. The prefecture cut down the trees that had died from pine wilt.” The prefecture cut down the trees about a year ago to prevent the damage from spreading due to pine wilt caused by pine beetles. The reason the pine trees are dying is that tiny nematodes, less than 1 mm in size, carried by the Japanese pine sawyer beetle, multiply inside the wood. When pine trees are affected by this disease, they are unable to absorb water from their roots and die. According to the Forestry Agency, pine wilt disease is the largest forest pest and disease in Japan. Although it had been on a downward trend in recent years, it increased in 2023 for the first time in 12 years, and is expected to increase in 2024 as well. Some local residents have suggested that the felling of Japanese red pines may have led to the rockfall. “It seems that when they cut down the pine trees and stripped the mountainside, the rocks started falling.” “There was a large rock, and they said it was going to fall any minute.”
■Nagano Prefecture denies causal relationship However, Nagano Prefecture denies any causal relationship. Naotaka Momose, head of the Forestry Division at the Matsumoto Regional Development Bureau of Nagano Prefecture, said, “Rockfalls are difficult to foresee and predict. There are various triggers, such as earthquakes, but in this case, we do not believe there is a causal relationship between the forest maintenance work caused by pine beetles and the rockfalls.” He also said that they do not plan to compensate the homes that were damaged. Several rocks that could potentially cause rockfalls still remain on the mountain where the incident occurred. What measures is the prefecture considering? “As a temporary measure, we plan to fill sturdy 1m x 1m plastic sheeting with soil and stack sandbags to construct a temporary protective fence.” (From the broadcast on May 13, 2026) [TV Asahi NEWS]
