Volcanic Violence
POSTED 21 OCT 2004

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

Caution: Has Mount St. Helens woken from her nap?

Mount St. Hellacious
Large mountain billowing smoke into the air. Click to enlargeMount 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 of 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."

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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.

person looks into instrument, crater in background.
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

Ten-cent guide to the volcano
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.

Graphic of lava traveling up through earth's crust.Magmatic 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?

The Why Files (home)

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Megan Anderson, project assistant; Terry Devitt, editor; S.V. Medaris, designer/illustrator; David Tenenbaum, feature writer; Amy Toburen, content development executive