At 34 miles, it's the world's longest bridge to cross a sea—an impressive $20 billion effort that will soon undergo its first major challenge from Mother Nature. The Hong Kong-Zhuhai-Macau Bridge is right in the sights of Super Typhoon Mangkhut, a powerful storm system that's headed right for that part of Asia, and though Quartz notes the structure was built to handle winds up to 125mph and stay standing even after a magnitude-8.1 quake, nerves are on edge. That's because, as of Friday, wind gusts were clocking in at up to 150mph at the storm's center, though they're expected to drop by the time Mangkhut arrives near Hong Kong on Sunday.
Structural engineer Ngai Hok-yan tells the South China Morning Post that how well the bridge fares will come down to wind direction and how high waves get near the artificial islands that are closest to Macau and in mainland waters. "If the waves are higher than [13 feet], then there is a chance [the] protective blocks will be washed away, and very quickly," Ngai notes. Some forecasts say the waves are anticipated to be as high as 20 feet. And if those barrier blocks disappear, the worst-case scenario? The island connecting the Hong Kong bridge portion to an undersea tunnel could itself be in trouble: Ngai says that tunnel could break loose, and the entire island could potentially collapse. Asia Times notes drone photos recently posted showed seawalls and tetrapods meant to protect the islands were "collapsing and drifting away," though officials claimed that was all part of the design. (Read more typhoon stories.)