not be large. While Rick is flying back from the conference, his colleagues in the field office finish plugging in the latest data for the eruption. To their horror, discover that the top of the magma chamber alone has more than enough eruptible magma to destabilize the chamber and trigger a super eruption. As they realize this, the volcano suddenly erupts violently, severely damaging the field office and injuring Jock. Matt investigates the eruption and contacts Dave about it to inform Rick. A pyroclastic flow forces the team to abandon the main USGS office and flee; Jock flees in the helicopter while Nancy and Matt flee in their truck, but the flow outpaces and kills them both. Rick contacts Dave, another team member who left before the eruption to set up a backup office in a hotel in Boseman. Meanwhile, the vent is blowing ash east across the US and across major commercial air routes, prompting FEMA to clear American airspace and take other protective measures. Rick's plane flies directly into the ash cloud, damaging the engines, and they make an emergency landing in Cheyenne. Rick and Ken decide to go to the FEMA office in Denver but are caught under the ashfall and decide to look for a nearby military installation instead. The motel roof collapses due to heavy ashfall after more caldera vents open, destroying the backup office and killing Dave. Rick and Ken both manage to reach the military installation safely. Weathering the eruption inside the installation, Rick makes contact with FEMA and determines that the vents are going to merge into one massive caldera in an eruption on the scale of the Huckleberry Ridge Eruption, the largest in Yellowstone's history. Government officials try to come up with a plan to save the 25 million people trapped by the ashfall, but Rick convinces them that they cannot possibly hope to do so; the ash will make it impossible for planes to safely evacuate people or drop supplies. Instead, following his advice, FEMA creates the "Walk to Life" program, telling people to walk through the ash to safety. One week after the eruption starts, the ground above the magma chamber begins to fall into the empty space left by the ejected magma, signalling the end of the eruption. However, the damage has been done; the lingering atmospheric effects causes a volcanic winter to occur. Much of the US