Yellowstone Volcano Observatory


by Linda Lennon

What do you do with the largest active volcanic system in North America? Watch it, very, very closely. That is exactly what scientists from the U. S. Geological Survey and the University of Utah are doing in Yellowstone National Park. On May 14,2001, the Yellowstone Volcano Observatory was established to monitor the extensive active system under the Park. Dr. Robert Smith of the Geophysics Program at the University of Utah, longtime researcher in YNP, has joined forces with Yellowstone Park expert Dr. Bob Christiansen of the U. S. Geological Survey, to study the volcanic system of Yellowstone National Park.Beneath the geyser studded surface of the Park exists a large magmatic body, and geologists want to know how, when, and if this huge volcanic system will erupt again.
Lava Creek Tuff

In order to understand the future of volcanic activity in Yellowstone, we need to examine the past. The volcanics of the Yellowstone Plateau have had a short but prolific history, geologically speaking.

The output of this volcanic system is monumental when compared to that of the systems with which we are familiar; yet it has only been around for 2.1 million years. There have been three cycles of eruptions . The first cycle began approximately 2.1 million years ago, and ejected 600 cubic miles of consolidated volcanic rock fragments (welded ash-flow tuff) from the Huckleberry Ridge Caldera. The second cycle of volcanism, approximately 1.3 million years ago, produced 67 cubic miles of Mesa Falls Tuff from the Island Park Caldera. The third cycle, which possibly overlapped the second cycle, began 1.2 million years ago and erupted periodically for 600,000 years, ending only 70,000 years ago. The third cycle produced 240 cubic miles of tuff from the Lava Creek Caldera. Compare these amounts with the output of the Mt. St. Helens eruption of 1980, a paltry one fourth cubic mile of ash. The Yellowstone system produced 1600 cubic miles of lava in addition to the more than 900 cubic miles of ash-flow tuff.

It takes more than an understanding of the history of Yellowstone Park’s volcanic activity to know what is occurring under the surface today. In order to visualize subterranean events, geologists use a variety of methods to observe both the surface and the subsurface of the Park. Careful monitoring of the volcanic system attempts to establish a baseline, and more importantly, to note any changes from the norm.

Changes could mean that magma (melted rock) is moving in the subsurface, or that geothermal pressures are building. Migration of magma can also cause earthquakes of various sizes and frequency, in addition to uplift or subsidence around the volcano. These signals can be measured by the Yellowstone Volcanic Observatory’s monitoring system and used both to learn more about the events beneath the surface, and to predict future volcanic activity. 

The volcano monitoring system consists of a combination of devices. For example, simple surveying of benchmarks on the highway system near Le Hardy’s Rapids revealed three feet of uplift between 1923 and 1985. From 1986 through 1993, the same area displayed subsidence (sinking), at approximately the same rate of a half an inch a year. Expansion and contraction of the magma beneath the surface of the Park can cause the ground to be displaced in this manner. Another clever way to measure ground deformation is through the observation of changes in ground “tilt” over time. By measuring ancient shorelines along the north shores of Yellowstone Lake, Kenneth Pierce of the U. S. Geological Survey has concluded that the north shore has moved up and down more than 100 feet in the last 9,000 years! Up and down motion of the volcano is not a one-time occurrence; it is cyclical and probably reflects movement of the magma below the surface. The volcano appears to be “breathing.” Geologists now hypothesize that this is normal, baseline behavior. However, uplift or subsidence at higher rates could signal increased sub-surface activity. Ground deformation can be measured more precisely using Electronic Distance Measurements, tiltmeters, Global Positioning Systems, and Satellite Radar Inferometry, which are sophisticated means of keeping track of ground deformations. 

Swelling of the magma chamber can have results other than ground deformation. As magma moves upward and expands, it can fracture the overlying rocks. Twenty-three seismometers have been deployed around the Park, and are being used to detect ground vibrations caused by magma movement, which result in small to medium sized earthquakes. (To view the “action” at any one of these stations, go to:

Interestingly, the velocity of waves resulting from these earthquakes can also be used to detect the location of the molten rock, or magma chamber, under the park. An increase in the intensity or frequency of earthquakes originating beneath the Park could possibly signal a change in volcanic activity. 
Geologists study the results of monitoring in and around Yellowstone National Park in order to learn about ongoing processes beneath the surface. Yellowstone is an example of the dynamic earth on which we live. The more geologists learn, the closer we will be to being able to predict future volcanic activity. The Yellowstone Volcanic Observatory is an opportunity for geologists to expand their working knowledge of the world under our feet.


Christiansen, Robert, L., 2001, The Quaternary and Pliocene Yellowstone Plateau Volcanic Field of Wyoming, Idaho, and Montana. U. S. Geological Survey Professional Paper 729-G.

Fritz, William J., 1985, Roadside Geology of the Yellowstone Country, published in Missoula, Montana by Mountain Press Publishing Company.

Good, John M., and Pierce, Kenneth L., 1996, Interpreting the landscapes of Grand Teton and Yellowstone National Parks; Recent and Ongoing Geology, published in Moose, Wyoming by the Grand Teton Natural History Association. 

Smith, Robert B., and Braile, Lawrence W., 1994. The Yellowstone hotspot. The Journal of Volcanology and Geothermal Research 61 (1994) 121-187.

Yellowstone Volcanic Observatory Website, maintained by the U. S. Department of the Interior, U. S. Geological Survey, Menlo Park, California, U. S. A. 

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