How technology detected a huge mine landslide before it happened

A 165-million-ton landslide rocked Kennecott Utah Copper's Bingham Canyon Mine on April 10, registering as a 2.4-magnitude earthquake in nearby Salt Lake City. The cascade of rock damaged giant trucks and digger machines, but not one of the 500 people who work the 2.75-mile-wide, 0.75-mile-deep pit was injured.

That's because Kennecott employees expected a slide months in advance. For years, the mine has used sensors embedded in its walls to detect stress in rock, and lasers perched on the pit rim to measure the position of hundreds of reflectors mounted to the mine face. New radar technology allows the company to detect changes as small as 1/100th of an inch in the distance between monitoring stations inside the pit and large areas of the mine wall every six to eight minutes.

Starting in February, Kennecott workers observed minute movements in the mine's northeast face and began shifting roads, utilities and buildings out of the way. Not long before the slide, movement increased to two inches per day. The morning of the slide, the company evacuated its workers. Kennecott officials estimated that the landslide damage would cut the company's production of refined copper by 50 percent, down from 163,200 tons in 2012.

• Energy & Industry