Northwest’s Dynamite Keg : Mt. St. Helens Is Still Now but May Be Building Toward More Eruptions

VANCOUVER, Wash. —  David Johnston stepped off the helicopter at timberline on Mt. St. Helens five years ago, the first scientist to fly over the volcano’s summit since it had erupted several hours earlier.

“This is an extremely dangerous place to be,” Johnston told reporters who gathered around him in the parking lot. “If it were to erupt right now, we would die.”

As Johnston spoke, the still, clear, early spring afternoon was punctuated by the rumble of avalanches and the cracking of ice on the volcano’s glaciers following a week of intensifying earthquakes.

After 123 years of silence, Mt. St. Helens was clearing its throat.

Johnston, 30, had survived the dangers of a restless volcano before. In 1976, he and six others had spent five frigid nights on the flanks of an Alaskan volcano after their helicopter crashed. They were rescued just 12 hours before that mountain erupted.

The U.S. Geological Survey scientist spoke prophetically about the threats of Mt. St. Helens. He spoke of superheated, glowing avalanches roaring down the sides of the volcano at speeds approaching 100 miles per hour. He told of devastating mud flows and hurricanes of ash.

“We’re standing next to a dynamite keg and the fuse is lit,” said Johnston. “We just don’t know how long the fuse is.

“I am genuinely afraid of it.”

Two months later, Johnson was dead. In the volcano’s cataclysmic eruption May 18, 1980, he was blown off a ridge by a blast that approached with almost supersonic speed. His body was never found.

Mt. St. Helens remains a dynamite keg with an unpredictable fuse. Scientists are still unsure whether the eruptive cycle that began March 27, 1980, with that first, small eruption has run its course or whether the volcano could explode again.

The volcano has been virtually quiet for more than six months--the longest period of stillness since it reawakened. There are indications that Mt. St. Helens may have gone back to sleep, but there are other indications, just as strong, that the volcano is still very much alive.

“We just can’t answer what comes next,” said Don Peterson, one of the top scientists at the USGS’s David Johnston Cascade Volcano Observatory in Vancouver. “There aren’t any black and white answers.

“Scientists have learned to cope with varying degrees of uncertainties.”

Since September, 1984, the seismic monitors ringing the mountain and installed on the lava dome in the volcano’s vast, eerie crater have recorded no major earthquakes. Other instruments show little or no swelling in the crater or on the dome, a craggy lump of rocks 800 feet high and almost half a mile in diameter.

The violent but brief steam bursts off the dome that periodically sent scientists scurrying for cover have ceased. The rate of the volcano’s lava production has gradually decreased since 1982.

“One interpretation is that it is storing up pressure,” perhaps for another eruption, said Peterson. “The other is that it may gradually be turning off.”

Sensitive measurements taken by a small plane flying over the volcano show Mt. St. Helens is still venting as much as 75 tons of sulfur dioxide a day. Parts of the dome still glow, and scientists expect the glow would dim, shrink and then disappear if the volcano were settling down.

“It could be going into a prolonged silence, or it could be building towards an eruption with an explosive component,” said Steve Brantley, another USGS scientist.

Scientists do not expect a blast like the 24-megaton explosion in 1980 that blew 1,300 feet off the top of the once snow-capped peak, left 57 people dead or missing, devastated 150 square miles of forest and blew an ash cloud around the world. Mt. St. Helens’ crater rim is now 8,365 feet tall.

But towering ash eruptions reminiscent of those of the summer and early fall of 1980 are a possibility. The volcano could also blast away parts of its lava dome, though scientists think it is unlikely that the entire dome could be destroyed in one mammoth explosion.

Mt. St. Helens also could continue to add to the lava dome in nonviolent eruptions.

The mountain has erupted 18 times since the spring of 1980. Five were explosive; the 13 others were dome-building eruptions occasionally accompanied by minor explosions.

Scientists say the typical eruptive cycle at Mt. St. Helens can last 50 years, but those 50 years can be laced with five-to-10-year stretches of inactivity.

“Whether the next event is in two months or two years, it will have an explosive component,” Peterson said.