Inside USGS No. 1, Robert Christiansen, Yellowstone

http://gallery.usgs.gov/videos/845 USGS emeritus geologist Robert Christiansen describes his career working on Yellowstone geology from the 1960's through 2014. Bob's work along with his USGS colleagues revealed the details of Yellowstone's explosive volcanic past including mapping and dating of past super eruptions 2.1 million years ago, 1.3 million years ago and 640,000 years ago.