Thousands Illegally Climb Mount Fuji During Off-Season, Data Reveals

Japan's Mount Fuji, a UNESCO World Heritage site, sees an estimated 10,000 people illegally attempt to climb its trails each year during its off-season closure, according to estimates from Japanese media and a location data analysis firm. Despite local governments legally blocking the mountain paths, the data indicates these measures are insufficient to deter climbers.

The "Yomiuri Shimbun" reported that Mount Fuji has four climbing routes: the Fujinomiya, Subashiri, and Gotemba routes on the Shizuoka Prefecture side, and the Yoshida route on the Yamanashi Prefecture side. These trails are only open from early July to early October. Outside of this period, the mountain is officially closed.

Given the extremely high risk of mountain accidents during the closed season, the trail management authorities, the Shizuoka and Yamanashi prefectural governments, have set up signs and barriers between the 5th and 6th stations, closing off all routes to the summit in accordance with the Road Act. Local governments also strongly urge the public not to enter the mountain from areas other than the designated climbing trails.

The "go" (合目) is a unit used in Japan to measure climbing progress, with the mountain divided into 10 stations from the foot to the summit.

However, the number of people who encounter mountain accidents during the closed season is not insignificant. According to data from the Shizuoka and Yamanashi prefectural police, a cumulative total of 79 people encountered mountain accidents between 2019 and 2025, with 19 fatalities.

As the Japanese central government and the local government organizations in Shizuoka and Yamanashi had not previously grasped the actual situation of climbers during the closed season, the "Yomiuri Shimbun," with the assistance of the Japanese location information analysis company Location AI, used mobile phone location data to analyze foot traffic on the climbing trails and estimate the number of climbers during the off-season from 2019 to 2025.

The results showed that, except for 2020, which was affected by COVID-19, an estimated 8,000 to 12,000 people attempted the climb each year in other years. The number of climbers was highest in June, before the opening of the season, and in September, shortly after the closure. By route, the "Fujinomiya route," which is accessible by car to the 5th station and has the shortest distance to the summit, accounted for about 50% of the total. By age group, individuals aged 50 and over constituted more than 50% of the climbers.

This data does not include foreign tourists visiting Japan. Considering that foreigners accounted for 20% to 50% of climbers during the open season, and that foreign nationals have also been involved in mountain accidents during the closed season, the actual number is likely higher than estimated.

A representative from the Fujinomiya City Hall in Shizuoka Prefecture, which manages the Fujinomiya route, commented on the analysis results, stating, "The number is larger than we imagined. We hope to cooperate with the prefectural government in the future to jointly develop more effective response strategies."

The survey used mobile phone data from residents within Japan, including location information and user data, covering 93 million devices. This data was obtained by Location AI from data companies, with personal characteristics removed and anonymized, from applications that users have allowed external use of.

During the analysis, the research team set up data capture areas between the 6th and 7th stations of each climbing route. They then adjusted the data based on Japan's population size and structure to estimate the daily number of climbers.