Copper deposits were discovered in the mountains around Ashio as early as 1550, but serious extraction began only in 1610, when two local households received a permit from the Tokugawa shogunate. Within a year, copper from the site was being presented to shogunate officials, and Ashio was formally listed as a government mine. For more than two centuries, its copper helped solidify Tokugawa rule and became Japan's chief metal export after 1685. But the mine's golden age arrived in 1877, when entrepreneur Furukawa Ichibei purchased the operation and enlisted the financial backing of industrialist Shibusawa Eiichi. Foreign engineers introduced modern extraction techniques. New veins were discovered. Production exploded -- from modest output to 2,286 tons by 1884, accounting for twenty-six percent of Japan's copper. By century's end, Ashio produced forty percent of the nation's total. The mountain that had fed a feudal economy was now powering an industrial one.

The expansion came with a cost the balance sheets never recorded. New Bessemer smelters pumped sulfur dioxide into mountain air, generating acid rain that stripped hillsides bare of vegetation. Arsenic and heavy metals poured into the Watarase River. Downstream fishing communities watched their livelihood vanish -- roughly 3,000 fishermen lost their income as fish populations collapsed. The 1890 flood was catastrophic: slag-contaminated silt spread across farmland, destroying crops on contact and rendering fields sterile for years. Residents developed chronic health problems from arsenic exposure. Women struggled to produce milk for their children. Politician Tanaka Shozo rose to the occasion, delivering a speech on the floor of the National Diet in 1891 demanding the mine's closure. His campaign lasted years, culminating in the 1897 Third Mine Pollution Prevention Order -- Japan's first significant environmental regulation. But the order came too late for the village of Yanaka, which the government demolished in 1904 to build a flood control reservoir. Tanaka moved to Yanaka in protest and died there in 1913.

The environmental crisis was not the only eruption at Ashio. On February 4, 1907, pit miners who had been demanding higher wages launched a violent three-day riot. It began underground in the Tsudo pits, where workers smashed the foreman's cabin, then spread to sections throughout the mine. By February 5, miners had cut telephone lines at the Sunokobashi pits and attacked officials in the Honzan Ariki tunnels. The third day brought the most destructive action: miners surged aboveground to loot the company store, set the fuel warehouse ablaze, and attack Mine Director Minami Teizo, who fled and was beaten twice before reaching a hospital. The prefecture governor called in the military, but three companies of troops arrived on February 7 to find the riot already spent. Authorities arrested 628 miners and prosecuted 182. The company fired all workers at two pits and forced them to apply for rehiring. Yet the riot achieved its core demand: on March 1, wages rose an average of 19.4 percent, and provisions for injury-related absences improved. The uprising triggered a wave of labor actions across Japan's mining industry through the summer of 1907.

The mine changed hands multiple times during the twentieth century but never escaped its troubled legacy. During World War II, prisoners of war were forced to labor in the tunnels. The Furukawa Mining Company continued operations until 1973, when import liberalization and depleting veins finally made the mine uneconomical. The Excavation Department closed for good, ending over 360 years of continuous mining. In 1980, the site reopened as a tourist attraction, inviting visitors to walk through the tunnels where miners had once worked and rioted. The bare mountainsides that acid rain stripped over a century ago are still undergoing reforestation efforts today. Ashio is now part of the city of Nikko, a place better known for ornate shrines and autumn foliage than industrial ruin. But the scarred ridges visible from the air tell a different story about what happened when Japan's appetite for copper outran its concern for the land.

Ashio holds a singular place in Japanese history as the incident that forced a nation to confront the environmental cost of industrialization. The disaster predated the Four Big Pollution Diseases of Japan -- Minamata, Niigata Minamata, Yokkaichi asthma, and itai-itai disease -- by half a century, but it laid the groundwork for every environmental battle that followed. Tanaka Shozo's crusade established the template for Japanese environmental activism: a local champion, a reluctant government, and communities caught between economic need and ecological survival. Today the mine's tunnels serve as a museum, and the Watarase River runs cleaner than it has in over a century. But the lesson of Ashio remains as relevant as ever -- that the true cost of extraction is measured not just in tons produced but in the rivers poisoned and the villages erased from the map.