Volcanoes: Nature's ticking time bombs
There are about 1,500 active volcanoes that scientists know of on Earth, but ask them when they might erupt and the answer is anytime - they don't know. Nor can they predict the severity of the eruptions. Scott Pelley speaks to volcanologists about three volcanoes around the world on 60 Minutes, Sunday, Jan. 5 at 7 p.m. ET/PT.