Nepal-Tibet floods: What is a glacial collapse, how common is it?

More than 1,500 people are missing across Nepal and China’s Tibet, including more than 800 foreign tourists, after rare flash glacial-lake outburst floods submerged towns and communities under a sludge of mud and water.

More than 270 people have been killed, but officials say the toll is expected to rise as rescue teams attempt to reach farther areas that have been cut off by the floods, with se...