Predicting the Next Big One

May 18, 2005 — -- At 8:32 in the morning 25 years ago today, Mount St. Helens woke up in a violent mood.

"Vancouver, Vancouver, this is it!" radioed David Johnston, a 30-year-old geologist with the U.S. Geological Survey who was stationed 5.7 miles from the rumbling mountain in Washington state.

That frantic message was the first report of the eruption and Johnston's last known words. He was killed along with 56 other people and countless wildlife as a bulge that had swelled for weeks from St. Helens' north side started rumbling down the mountainside at 200 mph.

The landslide ripped a cap off the mountain and popped it like a champagne bottle -- releasing pressure that had contained pools of magma below. The 1,300-degree magma exploded laterally and streamed from the mountain at between 50 mph and 80 mph, flattening 220 square miles of forest and paralyzing much of the inland with suffocating ash.

Johnston had apparently told others earlier that he was worried about an eruption, describing the mountain as "a dynamite keg with the fuse lit." But no one had expected it would explode with such fury.

Given the surprising ferocity of the 1980 eruption, some wonder: If another big explosion were coming from one of the planet's 600 or so active volcanoes, would we be able to see it coming this time?

Thanks to some new advances in seismology and physics, scientists say they're more confident about their abilities to predict the big eruptions. One approach is listening for unique, musical-like vibrations from volcanic structures, which may signal the upward movement of magma.

Another, more radical approach involves drilling inside volcanoes to "get inside the patient" and better understand the processes that lead to big blasts.

In the mid-1990s, Bernard Chouet and others began tuning in to a unique "humming" vibration made by volcanic mountains as steam and magma rise through the structures' cracks and fissures. The seismology readings were different from those coming from ordinary earthquakes. When an earthquake fault slips and cracks, seismographs reveal a sudden jumble of vibrations. Just before a volcano blows, however, the vibrations often appear as a single frequency.

"As the fluid moves through a lot of apertures and bends and turns, it creates a wave inside the fluid," said Chouet. "That creates a resonance that is similar to an organ pipe in which the sound you hear is the propagation of air pressure disturbance pumped inside the pipe."