The National Park Service issued a news release this afternoon in response to an internet claim that a steam cloud was produced by Sunset Crater near Flagstaff. NPS stated "...no activity has been observed on the ground by park rangers staffing the National Monument."
We're in contact with the NPS, National Forest, National Weather Service, county officials and no one has seen any evidence of activity. The purported plume coincided with smoke being carried from a controlled burn in the forest a few miles upwind of the site.
NPS made a good point in that each of the 600+ cinder cones in the field are one-time events, so reactivation after nearly 1,000 years would be unprecedented.
Here's the full NPS announcement: