Because such large eruptions can occur in Yellowstone, it has come to be known as a supervolcano. The heat from the large mantle plume beneath the park causes melting of the crust and accumulation of magma. Long-term accumulation of magma causes pressure to build and eventually the crust starts to crack and magma erupts catastrophically. So much magma is released that the magma reservoir below is depleted. This causes the crust to cave in and form a caldera.
The mantle hotspot that sits below Yellowstone formed approximately 17 million years ago. The Yellowstone volcano has been active for more than two million years, and over that time countless small earthquakes, volcanic eruptions, and other volcanic activity have occurred, including the formation of several large calderas during massive volcanic eruptions. Three large caldera-forming eruptions have happened in Yellowstone’s history; the first occurred 2.1 million years ago and expelled so much magma that a crater was created larger than the state of Rhode Island. The second eruption occurred 1.3 million years ago in Island Park in Eastern Idaho and the third occurred 630,000 years ago which formed the Yellowstone caldera as we know it today. These three eruptions were some of the largest in known history and were respectively 6000, 700, and 2500 times larger than the 1980 eruption of Mount St. Helens. With massive eruptions occurring every 600,000-800,000 years, people are beginning to wonder if Yellowstone is overdue for another Earth-shattering explosion.
If the Yellowstone supervolcano were to erupt today, it is very hard to predict the extent of damage it would cause. The most likely scenario would be that a lava flow occurs. 90 percent of the eruptions in Yellowstone’s history have been non-explosive lava flows where streams of molten rock pours from the crust relatively non-violently. If the worst-case scenario should occur – an explosive caldera-forming eruption – the degree of damage is still debated among scientists and data are often exaggerated by the media.
Some predictions say that enough magma would be released to fill the Grand Canyon more than 11 times. Enough ash would be released that several inches could accumulate even 1,000 miles from Yellowstone and lava released could reach as far north as Calgary and as far south as Los Angeles. Some even go so far as to say ash would block out the sun and cause a global cooling event. Scientists do agree that the effects would be catastrophic. Ash would likely blanket most of North America with ash cover in Wyoming and the surrounding areas being severe enough to smother many plants and animals. Breathing would become difficult due to poor air quality and many water supplies would be poisoned. Many scientists agree that a mass extinction would not occur. In the previous three eruptions there is no evidence that an extinction event took place.
When asked about another massive eruption occurring, Jacob Lowenstern, Scientist-in-charge at the Yellowstone Volcano Observatory, said, "If such an event were to occur today, it would devastate the global economy, halting most transportation within the US, paralyzing our electrical grid, killing millions of livestock, and cooling the planet for a decade or more."
Many scientists also agree that a large, explosive eruption is not likely to happen any time soon. The supervolcano will not likely erupt for thousands or even tens of thousands of years. The caldera has been monitored steadily for more than 30 years, and over that time it has remained stable. Lowenstern said that while monitoring the park’s conditions, the observatory found a couple of exciting earthquake swarms in 2008 and 2010 as well as some interesting cycles of uplift/subsidence of the caldera where the ground lifted 5-10 inches. But he stated that this isn’t remotely close to the kind of activity that would precede an eruption. There are no signs that lead scientists to believe an eruption will occur in the near future.
There are many notification and alert procedures in place to ensure that in the unlikely event of an eruption, people in the immediately affected areas would be notified of impending danger. The Yellowstone Volcano Observatory was founded in 2001 and is a collaboration of 8 organizations that is overseen by the United States Geological Survey (USGS). They are dedicated to monitoring volcanic activity in Yellowstone and are responsible for providing information and warnings of potential and ongoing volcanic activity. They do a variety of research, monitor earthquakes, ground deformation, and volcanic activity as well as creating different materials for public education. Although nothing can be done to prevent an eruption from happening, scientists are confident that they will be able to detect an eruption weeks, months, or even years before it takes place.
There has been a lot of talk in the media about increased volcanic activity at Yellowstone in recent years. A lot of this information is purely speculation and there is no scientific data to support it. Some things that may indicate a significant eruption are: hundreds to thousands of earthquakes per day, earthquakes higher than 4.5 magnitude, and significant land deformations. There are hundreds of tiny earthquakes in Yellowstone every year and some amount of geologic activity is expected in the area but it does not indicate an eruption is going to occur. Yellowstone is also known for its geysers, hot springs, and other geologic features, which also do not indicate any danger.
When asked about possible future eruptions Lowenstern said: "I don’t think one will occur in the next hundred years, or even in the next thousand. The odds are very much against it. And our geologic research indicates that current activity at Yellowstone is consistent with activity over the past 5 to 10 thousand years, a time period without volcanic eruptions. Nothing has happened to make us think that changes are afoot."
Special thanks to Jacob Lowenstern for his advice on this article.
USGS Yellowstone Volcano Observatory
National Parks Trips Media
Jim Peaco, National Park Service