Geology

The world’s most famous quarries attract attention for their part in iconic landmarks, but few are as unique as a series of sites that have supplied centuries’ worth of pumice rock for Japanese construction.

The small town of Oya, near the mainland Japanese city of Utsunomiya, is at the heart of this phenomenon where the igneous rock, aptly named Oya stone, has been quarried for houses, public buildings, walls and monuments.

Despite its light and porous features, Oya stone is a robust rock that is easily worked and can only be extracted in this region. The result of undersea volcanic activity 20 million years ago, it is thought the Oya stone reserves span 24km² area around the Oya township, totalling about 600 million tonnes. It came to rest in Oya, 100km inland, due to geologic uplift.

While Oya stone’s history dates back to the 17th century in Japan, the most intensive extractive period was in the 70 years between 1919 and 1986. Oya stone became ubiquitous in public works such as train station platforms, stairs, gates, walls and other structures such as the Matsugamine Catholic Church.

The stone later shot to prominence in Western societies when American architect Frank Lloyd Wright famously ignored the advice of Japanese architects to include the material in the construction of the Imperial Hotel in the Hibiya district of Tokyo.

According to the Japan Times, Wright was told that, given the large quantity of material required, it would be better for him to purchase an entire mountain. The hotel was eventually completed and survived a large 1923 earthquake but was later removed as part of rigorous post-war overhaul of the city’s landscape.

Tourist hotspot

Today, visitors can still see Oya quarried in pockets of the region, such as Kanehon, north of Tokyo. However, the original quarry site remains the true tourist hotspot, after local authorities converted it into a museum in 1979 to preserve the town’s rich history.

The Oya History Museum allows visitors to descend underground into the quarry where more than 300,000 m³ of stone were carved Oya History Museum by hand and, later, with modern stone-cutting machinery over the decades. The original quarry site is approximately 20,000m² in area and 60m at the deepest point, with a constant temperature of 8℃.

The large underground void is decorated with artwork, and many of the rooms are illuminated with various colours. Concerts, weddings, filming and other events are held in spaces that have been carved out of the mine.