Spectacular sinkhole in Japan's road, pipes in question

Rescuers are still trying to free the 74-year-old man, who is trapped and potentially buried under sewage and sediment. They have lost contact with him for seven days.

The cave opened up on a road in Yashio, a town north of the Japanese capital, on a Tuesday during rush hour.

The hole in the road, originally 5 metres in diameter, has continued to widen over the days, merging with a second, larger cavity that appeared nearby: the chasm now measures 40 metres wide and 15 metres deep, threatening the surrounding buildings.

To counter the unstable terrain, rescuers had completed a 30-metre access ramp on Saturday to bring cranes and heavy equipment closer and reach the driver. A second ramp has been started.

But those rescue operations were suspended on Tuesday, Koichi Yamamoto, a Yashio firefighter official, told AFP.

They are "hindered by the concentration of heavy materials, debris and asphalt and concrete slabs," he said. A "considerable" amount of wastewater has also accumulated and "flows constantly like a river," he added.

To limit this phenomenon, the 1,2 million people living in the area have been asked to limit showers and laundry, which has prompted "onsens" (traditional public baths) to open their doors for free.

Local authorities attribute the initial subsidence to rusty sewer pipes that may have allowed underground hollow spaces to appear.

These road subsidences are on the rise across Japan, with some 10.000 incidents in 2022, often linked to sewers in urban areas, according to the Ministry of Lands.

Shinya Inazumi, a professor of geotechnical engineering at the Shibaura Institute of Technology, points out to AFP the insidious corrosion that is eating away at Japan's water and sewer network.

Installed during the rapid post-war economic growth, "many pipelines have already exceeded their (50-year) lifespan and could therefore rupture elsewhere due to ageing," he warns.

According to an estimate by the ministry, 40% of sewer pipes will have exceeded their lifespan in just over 15 years.

Heavy rainfall events, made more frequent by climate change, can worsen failures.

"These days, rainfall can be extremely heavy and localized: a large amount of water seeps underground (...) at an incredible speed," aggravating the digging of underground cavities through erosion, explains Mr. Inazumi.

In 2016, a hole about 30 meters wide and 15 meters deep appeared on a busy street in the city of Fukuoka (southwest), caused by the construction of a subway. No one was injured and the street reopened after a week of work.