11-07-2025
Yokohama manhole lid possibly blown off in 'air hammer phenomenon'
Downpours on Thursday night in Yokohama City, near Tokyo, may have caused a manhole cover to blow off, allowing water to gush out onto streets.
The incident occurred at an intersection in Yokohama's Kohoku Ward shortly after 7:30 p.m. on Thursday. Water spewed out of the manhole and fragments of cracked asphalt were scattered on the road surface.
City officials suspect a massive amount of rainwater flowed into sewer pipes in a short time, compressing the air inside and increasing pressure in what is called an "air hammer phenomenon."
The officials say asphalt fragments struck three nearby vehicles. They say a 39-year-old mother and her 9-year-old son in one of the cars sustained minor injuries.
The Japan Meteorological Agency says its radar analysis shows that about 100 millimeters of rain fell in and around Kohoku Ward in the hour through 7:40 p.m.
Workers have engaged in repair work, including sealing off the manhole. The roads became passable by early Thursday morning.
City officials intend to take measures to prevent a recurrence, such as installing pipes in the manhole shaft to allow air to escape.
