1. Mount St. Helens: Back?
2. How volcanoes work
3. Science of prediction
4. Volcanic landscapes
5. Ultimate volcano
6. Ecology after the eruption
7. The youngest mountain
Mount St. Helens, one of the Cascade volcanoes along the Pacific
coast, is back to rumbling, gassing, belching and generally
making people nervous. She's quiet, then she's loud. A lava dome
is building inside the crater, sure evidence that molten rock is rising.
October 2004: Mount St. Helens in Southwest
Washington State is erupting again. The mountain is seen from the
Johnston Ridge Observatory. During the 1980 eruption, a hurricane
rock swept over this ridge, killing volcanologist Dave Johnston. Photo USGS
The mountain could go back to sleep. Or it could go ballistic without further notice:
"As long as this eruption is in progress, episodic changes in the level of activity can occur over days, weeks, or even months. Increase in the intensity of eruption could occur suddenly or with very little warning and may include explosive events that produce hazardous conditions within several miles of the volcano."
See the Classroom Activity Page for this story.
That's as far as the experts can tell us. We can't add much, except to remember her horrific sideways blast of 1980, which burned, crushed, buried or asphyxiated 57 people, most of them outside the official danger zone.
It was quite an eruption. As summarized in the book Volcano Cowboys (see bibliography), for nine hours the volcano released the energy of one atomic bomb every second. St. Helens triggered the largest landslide in recorded history -- enough rock and crud to fill a football field 600 miles high.
As the mountaintop lost 1,300 feet of height, the valley of the North Toutle River filled with 3 billion cubic yards of rock, ash, snow and ice. Some landslides moved so fast they surfed over the top of a mountain ridge and blew down the other side. About 230 square miles were severely damaged by the blast, landslides and ash deposits, and trees blew down seven miles away. Downwind, vast clouds of ash carpeted the Northwest.
Oct. 3, 2004: A U.S. Geological Survey scientist tracks Mount St. Helens with
electronic distance measurements. See the lava dome building inside the crater?
Photo: Gene Iwatsub, USGS
St. Helens, like all volcanoes, gets it power from heat deep inside Earth. In the months before the eruption, the surge of molten rock, or magma, inside the mountain triggered earthquakes that were the first sign of the coming chaos.
limbo: The lower you go, the hotter it gets. The upper mantle supplies the
magma columns that feed volcanoes.
At the surface, the rising magma showed itself as an ominous bulge inside the crater. When the bulge collapsed, it triggered the giant landslide. The removal of all that rock uncorked pressurized gas trapped inside the magma. The gas explosion caused huge blast waves and sent billows of ash skyward.
Details, details. Exactly how do volcanoes work?