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.

Tuning In to Volcanoes' Unique 'Notes'

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."

Chouet and others call this sound "long period activity." He has used it to predict the eruptions of Alaska's Redoubt volcano in 1990 and the Colombian volcano Galeras shortly before it erupted in 1994. Hundreds of lives were saved by the advanced warnings.

But looking for long period activity is no silver bullet. One problem is they can occur even within volcanoes that don't blow. For example, recent activity at Mount St. Helens has produced the unique resonant signals, but seismologists say it's very unlikely the mountain is about to erupt.

Seth Moran, a seismologist at the USGS Cascades Volcano Observatory, describes St. Helens as being in a "steady state." He says whatever magma has emerged from the mountain since the volcano perked up last October has been devoid of explosive gas -- like "flat champagne."

So why the long period activity readings?

"There are other potential ways of generating the events," Moran said. "At St. Helens, we're getting low frequency signals and they appear to be generated by the sliding of fairly solid magma as it rubs against the conduit. So St. Helens appears to be an enigma when it comes to these events."

The fact that different activities can generate the same vibration is one reason John Eichelberger argues one of the best ways to understand volcanoes is to get inside them.

Probing Volcanoes From Within

Last summer, Eichelberger, of the University of Alaska in Fairbanks, was part of a team that used specially equipped oil-drilling equipment to bore a tunnel directly into the main valve of Mount Unzen, a volcano in southwestern Japan that erupted in 1995. The $18 million project (funded mostly by the Japanese government) was a bold one and the first of its kind.

Drilling into an active volcano is a dangerous proposition and Eichelberger admits it was tough to get permission for the project. At first he had hoped to conduct the work on a volcano in the United States but settled for the Japanese volcano, after much paperwork. In the end, he said, "it didn't turn out to be dangerous" -- mostly because the inside of the volcano was surprisingly cool.

"The fact that it was so cool even after the 1995 eruption was in a way disappointing," he said. "But it was also an important result."

The readings from the drilling suggest that volcanoes cool their magma much more quickly than scientists have realized. Eichelberger says that might mean the recent stirrings at Mount St. Helens, for example, are not from lingering magma from the 1980 eruption, but from a new pool of magma that has gurgled up from Earth's depths.

By removing a sample of rock from the Japanese volcano's main valve, the scientists learned another key clue -- weak eruptions don't necessarily mean a volcano's plumbing is leaking.

Previously scientists had thought that minor "burps" from a volcano meant that as magma rises toward the surface, it lets off its gasses along the way through cracks and fissures in the volcano's main valve, or conduit. But Eichelberger says that instead, weak eruptions might just suggest the magma is traveling slowly up a sealed pipe and has time to let off steam along the way.

Eichelberger and his team have now set their eyes on a volcano in the Russian far east, which he believes will have a hotter interior.

"There is an awful lot we still don't know about what goes on inside volcanoes," he said. "The only way to understand them better is to get inside more volcanoes."

Lessons From St. Helens

Of course, learning from past volcanic explosions like the Mount St. Helens' blast is also key when it comes to improving prediction. Jon Major, a research geologist at the USGS Cascades Volcano Observatory, says the 1980 blast was eye-opening, to say the least. No one, for example, expected a landslide to trigger a lateral blast on that shocking day 25 years ago.

"Since the 1980 eruption, we've come to appreciate the fact that volcanoes can build up and then fall apart. The big landslide at St. Helens really opened the eyes of a lot of people." Major said. "That was a surprise, but I don't think that volcanoes are going to have many more tricks up their sleeves."