Each year over 330,000 visitors flock to Yellowstone National Park to see it's main attraction, Old Faithful. About every ninety minutes Old Faithful erupts shooting thousands of gallons of water into the air. If these visitors knew what forces where at work to create these eruptions they may no longer look at them with wonder. Instead of wonder they might look with fear.

Yellowstone Park is actually a Supervolcano. Old Faithful's eruptions are caused by super heated water which lies over a large pool of superheated magma miles beneath the parks surface.

Normally a volcano is formed when a column of molten rock, known as magma, rises from deep within the Earth, erupts on the surface, and hardens in layers forming the familiar cone shaped mountain we typically associate with volcanoes.

Supervolcanoes are different. These begin when large reservoirs of magma collect deep in the Earth's crust. Magma continues to collect as the reservoir grows to an enourmous size under extreme pressure.A super eruption occurs when the pressurized magma raises overlying crust enough to create vertical fractures that extend to the planet's surface. One by one, magma begins to surge vertically along these new cracks, which forms a ring of erupting vents. Eventually, as the vents merge with each other, the large cylinder of land within the ring has nothing to support it. The remaining earth above the chamber crashes down into the magma below. This collapsing crust forces additional lava and gasses out around the edges of the ring further increasing the violence of the eruption that is now hundreds of times larger than a regular eruption. When the eruption ends it will leave behind a caldera, or large crater, just like the one that forms Yosemite National Park. 

The last time their was a full-scale eruption of a supervolcano, the Lava Creek eruption, 240 cubic miles of dust and rock was propelled into the atmosphere. The human race was almost driven to extinction over 600,000 years ago.

If Yellowstone was to erupt today the results would be devastating. For people within hundreds of miles of the park death will be immediate. Those closest from the lava flows, those further out suffocated by volcanic ash. All of the United States would be covered in several inches of ash and the world would be in a volcanic winter for several years. Experts predict that 90% of the Earth's population would not make it.

The chance of a supervolcano erupting in a person's life time are very slim. On average, they occur about every 600,000 years. But if you remember that the last one happened about that long ago it makes you wonder if we are due for another.