"Smith does not paint the devastating picture portrayed in a recent TV docudrama but said smaller threats exist. For example, a lower-scale hydrothermal blast could scald tourists strolling along boardwalks. Emissions of toxic gases from the park's geothermal features also pose a threat. Five bison dropped dead last year after inhaling poisonous gases trapped near the ground due to cold, calm weather near Norris Geyser Basin. Stepped up monitoring and a new 24-hour watch office could lead to more timely warnings and help avoid human catastrophes at Yellowstone and nationally, according to the USGS." URL: http://www.msnbc.msn.com/id/7789918/ I saw some of the "docudrama" as well as a NGC pure documentary on this subject, which was very scary. It's not just a volcano, but a "supervolcano".