Selected one of Popular Sciences 50 Best of the Web.
Get Email Updates
Write to us and we will send you an email when a new feature appears on the site.
A Volcano Vindicated
May 17, 2000
Twenty years ago today, Mount St. Helens erupted, spewing ash and rubble into the air for hundreds of square miles. But while the cataclysm is properly described as a natural disaster, even clouds of volcanic ash can have a silver lining.
Over the past 20 years, scientists have used the data from the Mount St. Helens eruption to devise new methods of predicting other eruptions and preventing the huge losses of human life that sometimes come with them.
A mountain explodes
C. Dan Miller, a research geologist withthe United State Geological Survey, saw the May 18 explosion. "I was driving up Interstate 5, headed up to the north side of Mount Saint Helens with some parts and some batteries for our time-lapse cameras," he says. "As I glanced over at Mount Saint Helensthere was a beautiful blue skysuddenly I saw this mushroom cloud go up above the volcano and climb rapidly into the stratosphere."
Lava flow. File size is 1 MB. Please be patient. If you prefer to view the movie with RealPlayer, click here. clip courtesy of the National Museum of Natural History
At the time, volcanologists didnt know how to accurately predict a volcanic eruption. "Our ability to forecast [eruptions] was fairly primitive," says Miller. However, during and after the eruption, scientists gathered reams of data associated with the self-destruction of the mountain. By measuring Mount St. Helens girth and height, constantly monitoring her temperature variation, and continuing to learn and study the events leading to eruptions, volcanologists are increasingly confident of their ability to predict the timing of volcanic events.
New technologies like improved personal computers and the global positioning system have made volcanologists jobs easier, particularly in terms of allowing real-time monitoring. When combined with ground-based toolsseismic, geodetic, gravity, gas emission and thermal infrared equipmentit makes for better analysis and prediction. "Since the 1980 event, we have refined our hazard assessment techniques, and we much better understand hazardous volcanic events," says Miller.
The impact of volcanoes
In addition to the environmental devastation wrought by mud, ash and blast, fifty-seven people lost their lives when Mount St. Helens erupted. Miller says that the number of people killed each year by volcanoes is relatively minor, but as the population grows and people move to the rich farmlands surrounding volcanoes, the risk of death or injury from eruptions grows. Thats why USGS came up with the Volcano Disaster Assistance Program. This program assists local officials with monitoring volcanoes and, ultimately, accurately predicting when they will erupt. In 1993, the program saved an estimated 30,000 to 40,000 people when Mount Pinatubo in the Philippines erupted.
Another serious consequence of volcanic eruptions is the effect they have on air travel. "When aircraft encounter these clouds of ash, its a very dangerous situation," says Miller. Abrasion of windshields and aircraft skins and engine damage result from encounters with the fine-grained ash from volcanoes. "One of the most critical things to mitigate the effect of ash on air travel is to notify pilots and airlines of where the ash clouds are located, where the ash is forming and where to avoid it," notes Miller. Volcanic ash advisory centers around the world provide data to meteorology offices, which notify airlines to avoid the extremely dangerous clouds.
Mount St. Helens
Ancient Indian tribes in Western Washington called Mount St. Helens "Loo Wit Lat Kla," which means "person from whom smoke comes."
Mt. St. Helens is a young volcano, less than 50,000 years old. The mountain has undergone a series of eruptive and dormant periods. The modern mountain formation occurred about 3500 years ago. Eruptions have occurred in 1898, 1903, and 1921, in addition to the mountains most famous eruption in 1980.
Most volcanoes occur on plate boundaries, areas where the shifting plates of our planet meet or are splitting apart; this is also where most earthquakes occur.
Volcanoes are formed from extremely high pressure in the Earths molten core. This pressure causes part of the mantle, a layer of solid rock between the core and the Earths crust, to melt and move upward.
Magma is formed when mantle rock melts and migrates up through the crust.
Magma commonly comes in three forms: basalt, the most common form; andesite, which rises from the junctions of colliding plates; and rhyolitic, which can be generated from melted continental crust.
Lava is magma that has reached the Earths surface.
There are more than 1,500 active volcanoes on the Earths surface. In the 20th Century, more than 380 eruptions occurred.