Graphical Headline May 20, 2002
Keep One Eye Open
Four inches. If one of your students grew four inches during the time he was in your middle school or high school, it might not seem like a very big deal. But when a volcano grows four inches in four years, there's cause for alarm. Something is happening underground — and that something might just signal the events leading up to an explosive volcanic eruption.

Spectral data taken from the ASTER instrument on board NASA's Terra satellite was used to detect this small change in elevation of an area of land in the Three Sisters region of central Oregon, 60 miles east of Eugene. Like Mount St. Helens in Washington, the five Three Sisters volcanoes are part of the Cascades Range, a line of 27 volcanic mountains stretching from northern California to British Columbia. And, while none of the Three Sisters volcanoes has erupted in the last 2,000 years, this uplift of 4 inches over a period of 1996 to 2000 probably means that magma is on the move again. Subsequent data collection on the ground by United States Geological Survey (USGS) scientists have confirmed that the uplift is continuing.

There are 13 potentially active volcanoes in the Cascade Range. 11 of these 13 volcanoes have erupted in the last 4,000 years. 7 have erupted in the last 200 years. There have been more than 100 eruptions in the Cascades during the last 4,000 years. (Each volcano symbol in the diagram below represents anywhere from one to dozens of eruptions that may have occurred over a shorter period of time.) Next to Hawaii and Alaska, the volcanoes of the Cascade Range are some of the most active in the United States. And, considering that Hawaiian eruptions are of a quieter, less explosive nature, and that Alaskan volcanoes aren't near as many rapidly-growing population centers as in the Pacific Northwest, the Cascade "sleeping giants" may well be considered the United States' most perilous volcanoes.

Remembering Mt. St. Helens
Last Saturday, May 18, was the anniversary of the 1980 eruption of Mount St. Helens in Washington State. Exploding with the force of hundreds of nuclear weapons, the volcano blew out hot gases and ash that traveled at speeds of up to 200 miles per hour and flattened entire forests 20 miles away. 57 people died.

While Mount St. Helens is the most memorable volcanic eruption of most adult lives, it occurred before your students were born. Students can read an interesting account of one reporter's ten-year relationship with the mountain in the story, "Mount St. Helens, 20 years later: a reporter remembers."

Mount Rainier is a good example of a Cascade "sleeping giant." Rainier is the tallest volcano in the United States outside of Alaska, reaching 2.7 miles above sea level. More than a million people live nearby in such large cities as Seattle, Tacoma, and Yakima. The greatest threat to nearby inhabitants at Rainier isn't from an eruption blast, which could be enormous. Lava flows and pyroclastic flows would probably extend no more than a few miles past the surrounding National Park boundaries and are highly likely to travel east, away from the major population centers.

The greatest threat at Mount Rainier is from volcanic mudflows called lahars. Rainier is covered with more glacial ice than the rest of the Cascades volcanoes combined. Its slopes are already steep and unstable from the constant release of hot, acidic volcanic gases and water. In an eruption, a concrete-like slurry of volcanic rock, mud, and melted glacial water can begin rushing down valleys at speeds of up to 50 miles per hour, destroying everything in its path. This is a lahar. More than 100,000 people currently live on the deposits of previous Mount Rainier lahars. It is important for them to know ahead of time that they should evacuate; in a major eruption of Mount Rainier, anyone left in the path of a surging lahar might very well perish.

The volcanoes of the Cascade Range are under constant surveillance. Regional networks of earthquake sensors watch for unusual seismic activity beneath or near known volcanos. If suspicious rumblings occur, scientists at the USGS Cascade Volcano Observatory in Vancouver, Washington quickly send out teams with portable equipment to evaluate the hazard on-site.

More Links
Students will know about volcanoes in Hawaii and perhaps Alaska. But many other parts of the United States have volcanic histories. For information on individual states and regions, see America's Volcanic Past from the USGS.

The USGS Volcano Hazards Program provides Current Updates for U.S. and Russian Volcanoes updated every 15 minutes.

Ever wonder which volcanoes have erupted in the continental US since the Nation was founded? Check out these FAQs about volcanic eruptions.

The USGS maintains several different Web sites dedicated to volcanoes of a particular U.S. region. Students wanting more information should visit sites for the Cascades, Hawaii, Alaska, California's Long Valley, or Yellowstone.

Learn About the Problem
What is the difference between a volcano that might erupt this week and one that might never erupt? The United States Geological Survey (USGS) provides the following definitions in their Glossary of Volcano and Related Terminology:

An active volcano is one that is currently erupting or one that has erupted during recorded history and is considered likely to do so again in the future.

A dormant volcano is an active volcano that is not currently erupting and which has not erupted during recorded history, but is expected to erupt again in the future. A dormant volcano is still considered active.

An extinct volcano is a volcano that is not expected to ever erupt again.

A volcano may lie "sleeping" for centuries. Then it may become active for many years, spewing steam and ash and occasionally experiencing minor tremors, still without ever having a serious eruption. Most of the volcanoes of the Cascade Range have been active in this way — without major eruptions — for the last several hundred years.

However, dormant volcanoes aren't dead. They must be monitored closely so that scientists can give proper warnings and state and federal officials can determine if or when to evacuate local residents for their own safety.

While the volcanoes of the Cascade Range have been mostly quiet for the last few hundred years, the explosive 1980 eruption of Mount St. Helens is the exception that proves how "angry" these mountains can become when finally awakened. The greatest danger may be in forgetting that a scenic, seemingly tranquil mountain, such as Rainier, Hood, or Shasta, can one day erupt with the same fury as Mount St. Helens.

Fire and Ice
Most people know that large volcanoes can have an impact on regional and global climate by putting large amounts of gases and dust into the atmosphere. But a University of North Carolina professor, Dr. Allen Glazner, recently reported on his research showing that changes in climate may cause volcanic eruptions.

Glazner reported in December that his data shows that volcanoes in California tended to erupt between glacial cycles. When glaciers retreated, volcanoes became more active. The implications of global warming and retreating glaciers worldwide might be an increase in volcanic activity.

Think About the Problem
An ideal warning of an impending volcanic eruption would be one that would predict not only when and where the eruption would occur, but also pinpoint how big of an eruption it would be, whether it would be accompanied by ash or mud flows, etc. And that warning would need to come early enough for emergency management officials to have time to decide just what to do — to issue alerts or to actually evacuate the nearby area.

  • Students can read about the challenges involved in predicting eruptions in the Riverdeep Current article, "Volcano Chasers."

  • Can We Predict Volcanic Eruptions? is a site from the Annenberg/CPB Project that provides a multimedia presentation of the science of volcanoes and of predicting eruptions.

Extending the Problem
Help students understand the challenges involved in deciding to evacuate residents from near a volcano. Ask students:

  1. What are five possible negative results if a community is evacuated weeks before a volcano actually erupts?

  2. What are five possible negative results if a volcano has a large eruption and local communities have not been evacuated?

  3. Has your community ever suffered a severe weather event, such as a hurricane, a tornado, a severe blizzard, or a flash flood? What kind of warning were you given? What advance preparations did your family make? How much warning would you want to have if the event were to recur?

  4. Students might find it interesting and informative to read Volcano Hazard Assessment reports for volcanoes in Washington, Oregon, and California. Have students pick a volcano and discuss the types of volcanic hazards (e.g., pyroclastic flows, lahars, etc.) the hazard assessment report describes for that volcano. What types of things do public safety officials use when drawing up hazard-zonation maps?

Choose whichever of the following events is most likely to strike your community: volcano, earthquake, hurricane, tornado, blizzard, flash flood, forest fire. Have the students prepare a safety and preparedness guide for the community. Here are some possible resources:

  • For specific information on surviving volcanic activity, see What to do if a volcano erupts from the USGS.

  • FEMA's Emergency Preparedness Checklist can help outline the steps for creating an emergency plan and preparing emergency supplies.

  • California Preparedness Materials from the Red Cross are available in 12 languages. Include documents on such subjects as "Disaster Supply Kits" and "Earthquake Tips for People with Disabilities." (Documents on this site require the use of the Adobe Acrobat® Reader plugin.)

  • FEMA for Kids is a site on disaster preparedness aimed at younger grades. Herman, the site's "spokescrab," discusses his own search for a disaster-proof shell.

The instruments on NASA's Terra satellite have provided scientists with important new data for monitoring volcanic activity. Chiliques, a volcano in northern Chile, was thought to be dormant until Terra's ASTER instrument discovered hotspots in the volcano's crater and on its flanks. Together with improvements in the more traditional monitoring techniques, such advances may someday allow scientists to predict when the sleeping giants will awaken once again.


Mount Philadelphia?
Perhaps your students feel that, because they don't live in Oregon or Hawaii, they don't need to worry about volcanoes. What if you told them that the Atlantic Ocean floor is going to slide beneath North America, forming a subduction- zone trench 2,000 miles long, and that volcanoes would begin forming a new range of mountains along the eastern US coast?

Relax. Researchers at the University of Minnesota say that the trench probably won't start forming for another three to ten million years. It may take millions more years before the first volcano erupts. For more on the story, see the press release from Science Daily.

More Links
NASA Classroom of the Future/ Volcanoes: In this role-playing module, students are presented with four theoretical situations (e.g., whether or not to build a new high school in the shadow of Mt. Rainier) and asked to evaluate data and make public policy decisions.'s Trouble in Paradise is based on a Discovery Channel broadcast reporting on what it's like to live on the Caribbean island of Montserrat, which lies in the shadow of an active volcano.

Volcanoes continue to create new islands, rising thousands of feet from the Pacific Ocean floor until they ready the water's surface. Read more in the Riverdeep Current article, "Volcanoes Beneath the Sea."