Should the same happen again, the ground around Yellowstone National Park would rise upwards forming a swarm of earthquakes.
Then, following the eruption, enormous pyroclastic flows would blast their way across the park.
This mixture of ash, lava and superheated gas exceed temperatures of 1,000C and can move at speeds of up to 300mph.
They are predicted to spread more than 100 miles out from Yellowstone, burying states like Wyoming, Montana, Idaho, and Colorado in three feet of life-extinguishing volcanic ash.