This is a tad frightening.
NARRATOR: Yellowstone is America's first and most famous National Park. Every year over 3 million tourists visit this stunning wilderness, but beneath its hot springs and lush forests lies a monster of which the public is ignorant.
PROF. ROBERT CHRISTIANSEN (US Geological Survey): Millions of people come to Yellowstone every year to see the marvellous scenery and the wildlife and all and yet it's clear that, that very few of them really understand that they're here on a sleeping giant.
NARRATOR: If this giant were to stir, the United States would be devastated and the world would be plunged into a catastrophe which could push humanity to the brink of extinction.
PROF. ROBERT SMITH (University of Utah): It would be extremely devastating on a scale that we've probably never even thought about...
BBC Horizon - SuperVolcano Program Transcript