Diving into mysterious Crater Lake

Researchers here are going deep into the giant volcanic hole with aquatic robots and highly sensitive sonar. The lake, formed by a massive eruption 7,700 years ago, is one of the world's purest bodies of fresh water and, at 1,932 feet, one of its deepest. Most interesting to scientists, it's had little mixing with the outside world--no feeder creeks, no rivers, just snowmelt and rainwater.