The Yellowstone Caldera, also known as the Yellowstone Supervolcano, is a volcanic caldera and supervolcano estimated to be an area of about 34 X 45 miles (55 X 72 km).
Nobody is sure, it last erupted 700 000 years ago. Its eruption could produce enough ash to layer the atmosphere with 5 feet of ash, and will knockout everything and body within 1000 mile radius so when it erupts places such as Denver and Cheyenne are at risk.
Yellowstone National Park is a super volcano. Yellowstone is over a "hot spot" which is why there are geysers there. The hot spot blew millions of years ago leaving a caldera where the geysers are. Yellowstone is a volcano but do not go expecting an eruption unless you can wait a few million years.
What would happen if Yellowstone were to erupt? If the supervolcano underneath Yellowstone National Park ever had another massive eruption, it could spew ash for thousands of miles across the United States, damaging buildings, smothering crops, and shutting down power plants. It'd be a huge disaster.
No one big super volcano :)
707 miles
Yellowstone is about 1,026 miles from Phoenix.
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