A gigantic volcano lies under the western United States. For the last 70,000 years, it has been mostly quiet. If that ever changes, it could be devastating.
The "supervolcano" is located beneath Yellowstone National Park, which is a giant park that extends through Wyoming, Idaho, and Montana. The volcano itself is in northwestern Wyoming. About 6-10 kilometers (4-6 miles) beneath the ground is a large chamber filled with magma, or molten rock.
Volcanologists, or scientists who study volcanoes, have been observing the supervolcano since 1923. Recently, the volcano has been more active than usual. Some scientists wonder if that means it might erupt soon. The eruption of such a large volcano could cause serious damage.
Other experts say there's no need to worry. Dr. Jacob Lowenstern is the lead scientist in charge of monitoring the Yellowstone volcano. He says the volcano is currently dormant, which means it shows low levels of activity.
"There is nothing to show at this point in time," says Lowenstern.
A Little Shaking Going On Inside
Underground activity is common in the area. Yellowstone averages between 1,000 and 3,000 earthquakes a year. Most of these are so small that they can't even be felt. Because earthquakes and volcanoes are closely related, these tremors can indicate that things are happening inside the supervolcano.
Even with the recent increase in the volcano's activity, scientists don't think that it will erupt anytime soon. It hasn't always been so quiet, however.
Geologic evidence suggests that Yellowstone has had three huge eruptions in the past 2.1 million years. These eruptions occurred about 600,000 to 800,000 years apart.
The Yellowstone supervolcano collapsed on itself after each of these major eruptions, sucking trees, boulders, and even mountains into the crater that formed. This hole is called a caldera. The Yellowstone caldera is currently 30 miles wide and 45 miles long.
Each of these eruptions spewed huge amounts of volcanic ash, gas and magma into the air. The debris covered most of the continental U.S. Some have even been found as far away as Louisiana.
The most recent Yellowstone huge eruption occurred about 640,000 years ago. The blast shot so much debris into the air that it blocked out the sun across much of the continent. Rivers of lava, rocks and ash called pyroclastic flows swept through the region. Magma spewed out of the ground and charred the landscape.
Scientists say that that eruption was 1,000 times greater than the 1980 eruption of Mt. Saint Helens, which killed 56 people and thousands of animals. It also scorched hundreds of miles of land in Washington and Oregon.
Maybe Some Lava Flows
The United States Geological Survey (USGS) is a government science group that studies Earth. They agree that the likelihood of another massive eruption of the Yellowstone volcano is very slim.
Instead, they believe that the volcanic activity may cause more minor events. The underground heat could cause steam or hot water to shoot from the earth. It could also result in lava flows, or slow-moving rivers of lava, that ooze out of the ground over a period of days, months, or years.
Lava flows are much less destructive than a major eruption. They are also quite rare. The last lava flows in Yellowstone took place about 70,000 years ago. Since then, the flows have hardened into layers of rock. Evidence of lava flows can be found in the cliffs near Old Faithful. Old Faithful is a geyser, a tall column of burning hot water and steam heated by magma underground. It erupts every 45 minutes to 2 hours and is one of Yellowstone's most popular attractions.
The Yellowstone volcano has been mostly quiet for thousands of years now, but that doesn't mean that it will stay that way forever. Scientists aren't sure when to expect the next eruption, or how much damage it would cause. To most experts, however, that day is still a long way off.
Dr. Steven Anderson is a volcanologist at the University of Northern Colorado. "We are getting into the time period where it is supposed to become more unstable," says Anderson, "but I am not holding my breath."