Supervolcano.

Yellowstone is a park, but it's also the deadliest volcano on Earth. Beneath it, a sleeping 'dragon' is stirring. When an earthquake opens a crack for magma to seep through, other warning signs of an eruption start popping up, but they are ignored or dismissed as 'minor'. But when they learn an eruption will happen, panic breaks out through people of the USA and the world.