An eruption of a supervolcano would have a catastrophic effect on life all over the planet but especially on the plains states of the U.S. The volume of extruded magma in a supervolcano is large enough to radically alter the landscape and to severely impact global climate for years, with a cataclysmic effect on life.
Volcanologists have been tracking the movement of magma under the park and have calculated that in parts of Yellowstone the ground has risen over seventy centimeters this century.
The most recent caldera-forming eruption at Yellowstone occurred about 650,000 years ago and it produced a caldera 53 x 28 miles (85 x 45 kilometers) across what is now Yellowstone National Park. During that eruption, ground-hugging flows of hot volcanic ash, pumice, and gases swept across an area of more than 3,000 square miles. When these enormous pyroclastic flows finally stopped, they solidified to form a layer of rock called the Lava Creek Tuff. Its volume was about 240 cubic miles (1,000 cubic kilometers), enough material to cover Wyoming with a layer 13 feet thick or the entire United States with a layer 5 inches thick. The Lava Creek Tuff has been exposed by erosion at Tuff Cliff, a popular Yellowstone attraction along the lower Gibbon River.
The eruption also shot a column of volcanic ash and gases high into Earth's stratosphere. This volcanic cloud circled the globe many times and effected Earth's climate by reducing the intensity of solar radiation reaching the lower atmosphere and surface. Fine volcanic ash that fell downwind from the eruption site blanketed much of North America. This ash layer is still preserved in deposits as far away as Iowa, where it is a few inches thick, and the Gulf of Mexico, where it is recognizable in drill cores from the sea floor. Lava flows have since buried and obscured most of the caldera, but the underlying processes responsible for Yellowstone's tremendous volcanic eruptions are still at work. Such an eruption would disrupt global climate by injecting millions of tons of ash into the atmosphere. Some of the ash would remain in the atmosphere for years, reflect sunlight back into space and cool the planet, significantly effecting life. In addition, a blanket of ash over a meter thick would be deposited in nearby regions and effectively smother life there.
BBC had a report on supervolcanos in which they stated, "Scientists have very few answers, but they do know that the impact of a Yellowstone eruption is terrifying to comprehend. Huge areas of the USA would be destroyed, the US economy would probably collapse, and thousands might die."
Seismic activity in the area could presage an eruption. Earthside.com is monitoring and reporting such activity.
The U.K. version of Yahoo News reports:
Slumbering supervolcanoes powerful enough to wipe out much of the planet may awaken much sooner than it had previously been thought. Experts believed it would take hundreds of thousands of years for reservoirs of molton rock, or magma, beneath a supervolcano to build for an eruption.But a new study indicates the time between super-eruptions can actually be tens of thousands of years - and many are already long overdue.
A blast from a supervolcano would be strong enough to cause mass extinction and change the world's climate.
The findings, published in the Journal of Petrology, are bad news for anyone living in the centre of the US.
An overdue monster supervolcano is hidden underneath one of the country's premier holiday spots - Yellowstone National Park in Wyoming.
The last blast there, which occurred more than 600,000 years ago, covered half the US - around 3,000sq miles - with volcanic ash.
Researchers in New Zealand analysed zircon crystals, which grow within volcanic magma, to calculate how long build up takes before eruptions.
Their answer was no more than 40,000 years - a relatively short time in geological terms. Supervolcanoes are estimated to carry a force thousands of
times that of a normal explosion. They spew thousands of cubic yards of ash,
dust and poisonous sulphur dioxide into the atmosphere and create a giant crater, or caldera.
Recent measurements indicate that over the past century the earth above the Yellowstone magma chamber has risen almost 19 inches. Scientists say this is telling evidence of pressure building below.