The Volcano Beneath Yellowstone

The Volcano Beneath Yellowstone
The "Yellowstone Supervolcano" produced some of Earth's largest eruptions.

Volcanoes at Yellowstone?
Yellowstone National Park is world-famous for its geysers and hot springs. Those thermal features are easy-to-observe evidence of an active magma system beneath the Park. This magma system has produced some of the largest volcanic eruptions in Earth's history - eruptions so large that they have been called "supervolcanos". One of these eruptions produced a caldera that is about 50 miles across.

Should you be concerned about this? Here are three facts... 1) the most recent super eruption occurred about 640,000 years ago; 2) scientists monitoring the activity at Yellowstone today say "nothing unusual is happening right now"; and, 3) a gigantic eruption is expected to be preceded by significant warnings.


What is a Supervolcano?
A supervolcano is an eruption that rates a magnitude of 8 on the Volcanic Explosivity Index. The VEI is a scale that rates eruptions on their ejecta volume, plume height and duration. The scale ranges from 0 through 8. Only a few dozen eruptions in all of Earth's history are known to have a VEI of 8. Two of those eruptions, the Lava Creek eruption (640,000 years ago) and the Huckleberry Ridge eruption (2.2 million years ago), occurred at Yellowstone. These eruptions were given the VEI rating because their ejecta volume exceeded 1000 cubic kilometers!


How Active is the Yellowstone Volcano?
The Yellowstone Volcano Observatory closely monitors earthquake activity, ground deformation, streamflow and stream temperatures in the Yellowstone area. Occasional earthquake swarms occur, the ground surface changes elevation and streams change in both discharge amount and temperature. They have no evidence to suggest that a volcanic eruption of any size will happen at Yellowstone in the forseeable future.


When Was the Last Yellowstone Eruption?
The most recent volcanic eruption at Yellowstone occurred about 70,000 years ago and produced the lava flows of the Pitchstone Plateau. The lava flows of this eruption covered an area about the size of Washington, D.C. and are up to 100 feet thick.


What Causes This Volcanic Activity?
There is a hot spot beneath Yellowstone. A hot spot is a persistent plume of hot material rising through Earth's mantle. This rising plume delivers heat to the area, causes forces in the crust that produce earthquakes and rarely produces a volcanic eruption. A hotspot is also responsible for the volcanic eruptions of Hawaii.


What Causes the Geysers?
The magmatic activity below Yellowstone causes rock beneath the Park to be much hotter than subsurface rock in other areas. Water that falls as rain or snow above these rocks can infiltrate into the ground and enter the ground water system. Some of this water encounters the hot rock below and is heated to well above the boiling point. This water remains a liquid because it is under the enormous pressure caused by the weight of the overlying rock. The result is a "superheated" water which can reach temperatures of up to 400 degrees Fahrenheit.

The superheated water is less dense then the cooler water above it. The less dense, superheated water is thus buoyant. This instability causes the superheated water to rise towards the surface through pore spaces in the overlying rock. some of it will find its way into the cavities that feed the geyser system and be blasted back to the surface in an eruption.