Mud erupting from a fissure in Surabaya, Indonesia, has made a terrible mess of things—swamping houses, filling streets, chasing people out of their homes. At a loss, local engineers came up with a crazy solution: dropping giant concrete balls into the hole. Even crazier: it worked.

Each of the concrete balls weighs 88 lbs. In a February trial run, the engineering team dropped 16 balls into the hole; favorable results motivated them to toss in more. By the end of the effort, a total of 1500 orbs will have been dropped into the crater—supposedly created by drilling activity at a gas field on Java Island—to stem the mud flow that, at its peak, poured out the equivalent of 1 million barrel drums each day.