World: The Murderous Mountain

For days the rain had been falling, soaking the bleak Welsh coal-mining village of Aberfan and the 800-ft. slag heap towering above it like a black, oozing Everest. Then one morning last week, David John Evans, a maintenance man with a local colliery, climbed to the top of the waste heap to look into reports that the gigantic mass was moving. With a shock, Evans discovered that it was. "Suddenly I saw the heap shifting," he recalled later. "The movement was like thunder. I could hear trees on each side being crushed to matchwood."

Undermined by water pouring down its slopes, the...