Yellowstone Supervolcano

It was a summer morning in 2003, and the park ranger was guiding tourists at Norris Geyser Basin in Yellowstone National Park. She noticed the smell of burning sap, and inferred that the roots of the pine trees must be heating up. A thermometer inserted into the ground along the trail revealed that it was over 100°C. The park's geologist was alerted, and the area was marked for special monitoring.

Unsuspecting tourists

Each year, millions of visitors enjoy Yellowstone's scenic waterfalls and mountainous landscape. The park also hosts 10 thousand thermal features, including "Old Faithful," colorful hot springs, and gurgling mud pots. The geologists at Yellowstone Volcano Observatory are acutely aware of the source of the thermal energy that fuels these features. Beneath their feet lies what some call the largest and most explosive volcano on Earth.

Trail blazed by the hot spot

Yellowstone is fueled by a hot spot that has been active for nearly 17 million years. In time, as the North American Plate moved over the hotspot, magma buoyed upward from beneath the crust. Parts of the crust heated and melted into the reservoir of magma below. As gases accumulated, so did the pressure. The crust expanded. Eventually the crust ruptured, and the molten rock exploded in a series of super eruptions. The most recent eruptions occurred 2.1 million, 1.3 million, and 640,000 years ago. As the North American plate passed over the hot spot, it left a trail of extinct volcanoes from Oregon to Wyoming.

Eruption of a supervolcano

An eruption similar to the ones at Yellowstone has not been seen in human history. Consider the eruption of Mount St Helens, shown on the map in Figure 1. Its eruption blasted out the north side of the mountain, ejecting a cubic kilometer of ash into the sky and leaving a crater 1.6 km wide.

In comparison to Mount St. Helens, the last three major eruptions at Yellowstone left a caldera over 50 km wide. The most recent eruption of the Yellowstone supervolcano ejected 1000 km' of ash, enough to cover most of the Western United States under several feet of ash, and darken the skies of the planet, resulting in a global winter.

Tracking the giant

Geologists have developed a network of systems to monitor the activity of Yellowstone volcano. Seismometers across the park record the thousands of earthquakes that shake the area each year. Ultra sensitive Global Position System devices send a constant stream of data showing the precise movement of the ground as it rises and falls in cycles. Geologists sample the water in the rivers, analyzing changes in the temperature, discharge, and chloride concentration. They know it is not a matter of if the Yellowstone supervolcano will erupt again, but when it will erupt. This is exactly why they will continue monitoring this site long into the future.

Teacher's Edition for Yellowstone's Supervolcano

Purpose

Students will apply what they have learned about Earth's internal processes to the case study of a real volcano. They will learn about how geologists use a combination of precision instruments to monitor volcanic processes.

Background

The discovery of new thermal activity at Norris Geyser Basin in 2003 at Yellowstone spurred a media frenzy and even inspired a docudrama about the eruption of the supervolcano. While eruptions of a supervolcano are indeed cataclysmic, they are extremely rare. Geologists predict that such an eruption at Yellowstone is unlikely for thousands of years. Eruption precursors could include an increased frequency and intensity of seismic activity, land deformation and uplift, changes in heat flow, increased gas emissions, and changes in the hydrology in the area.

Teaching Strategies

• Before they read this feature, ask students what they know about Yellowstone National Park. Some might have visited the park, or have heard about its famous geysers which erupt with characteristic regularity.

• Have students recall the layers of the Earth. Ask volunteers to come to the board and draw and label the crust, the mantle and the core.

• Tell students that this feature mentions a type of volcano associated with hot spots. Use the diagram produced by your student volunteers in the previous bullet to show students how a hot spot is created by a plume of magma welling up from within the mantle. This will help students visualize the processes highlighted in the feature.

• After reading, ask students to speculate how an eruption of the Yellowstone supervolcano would affect the people in your state. Much of Wyoming would be covered beneath hundreds of meters of lava flows. The Western states would be buried beneath several feet of ash, devastating all agricultural production in the region. Sunlight would be blocked around the world, and average global temperatures would plunge for years.