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Unpredictable Mount St. Helens

By Peter Potterfield - May 27th, 2005

As professional volcanologists, amateur volcano watchers and nearby residents nervously monitor increased activity at Mount St. Helens in Washington State, few are aware of the long, volatile history of the mountain. The peak had been dormant since Europeans arrived in the Pacific Northwest in the 18th century, giving the local settlers a false sense of security. But local Indian tribes had long regarded St. Helens with a wary eye. Ancient legends passed down from prior generations warned that this beautiful peak was renowned for dropping "hot rocks" and dangerous avalanches of debris--called lahars and pyroclastic flows--onto the surrounding countryside.

In the decades prior to the spring of 1980, Mount St. Helens was perhaps the most obscure of the Cascade volcanoes. Very much in the shadow of her bigger, glacier-clad sisters such as Mount Rainier or Mount Adams or Mount Hood, St. Helens was lower in altitude than all of those. Even if it's Mount Fuji-like cone was the most perfect of all the mountains of the Pacific Northwest, it remained little known, except to outdoor lovers. St. Helens was for decades a favorite of many Cascade climbers and hikers.

"St. Helens was always a fun climb," remembered pioneering Cascade climber Keith Gunnar, who in the early 1950s worked as an engineer at Boeing but who was an avid recreational climber. "It was close enough and small enough that you could climb it as a day trip: drive down on Saturday, sleep by the car, and start around midnight for the top. You could be back at home in time for Sunday dinner."

Fred Beckey's famous Cascade Alpine Guide of the day notes the peak was seen by both Lewis and Clark as well as Captain Cook. Beckey describes the Dog's Head route, the so called "normal" way up the peak, as a Grade I, with the steepest slope only about 30 degrees. At only 9,677 feet (as opposed to Rainier at 14, 410), the mountain offered all the fun of climbing a Cascade volcano without the seriousness. You could do it as a day climb, or even camp on the summit. The big timber around the base of the mountain, particularly near scenic Spirit Lake, made the entire area one of the most appealing in the range.

But all that changed on May 18, 1980, when St. Helens erupted violently, blowing off the entire north side of the peak into the air. The explosive eruption removed more than a cubic mile of material from the mountain, and reduced it's elevation from 9,677 to 8,365. Not just the mountain itself, but the landscape of western Washington state was completely transformed as pyroclastic flows roared down the flanks of St. Helens, filling in lakes and river, destroying forests, and sending torrents of debris flows down the drainages. Ash clouds turned day into night in cities east of the Cascade mountains, as far away as Montana. Scientists said the ash from St. Helens' eruption entered the jet stream and completely circled the globe.

More than 60 people--including loggers, climbers and campers--lost their lives in the eruption, despite the fact that St. Helens had been smoldering, shaking and venting ash for months before. While US Geological Survey volcanologists had warned of an impending eruption, even they were taken by surprise by the cataclysmic event that occurred that quiet Sunday morning of May 18. The eruption was so violent it could be heard as a loud "boom" in Seattle, more than 100 miles away. Rivers swollen by melting glaciers swept away highway bridges, closing Interstate 5. Residents from Seattle to Portland wondered what the eruption might foretell of other volcanic eruptions in the range. The St Helens event was devastating, but the effects were minimized by its location far from population centers. Residents of the Pacific Northwest knew that a similar event at Mount Hood or Mount Rainier could spell doom for the region's largest cities.

Since that eruption, the mountain--and the rest of the Cascades--had been relatively quiet until the fall of 2004. In the mammoth crater that was blasted open by the eruption, a lava dome began to slowly grow shortly after the 1980 event. This gradual rebuilding the peak was merely another chapter in the eons-old geologic process that has given birth to all the Cascade volcanoes: a violent cycle of eruption and devastation, followed by a gradual rebuilding through the venting of magma--liquid rock that reforms the peak time and again.


In the 25 years since that cataclysmic 1980 eruption, life had returned to normal on St. Helens. Humans and wildlife alike adapted to the changed landscape. Plants and trees gradually took hold in the surprisingly fertile volcanic soil. Climbers and hikers returned to the mountain for a very different but still enjoyable experience. A national preserve was established--the Mount St. Helens National Volcanic Monument-- and elaborate new visitors centers build at the entrance, and on Coldwater Ridge, at 2,500 feet, deep in the blast zone. On Johnston Ridge, a striking vantage point just five miles from the mountain, an observation point was built at a place where people had died during the eruption. It was named after a geologist, David Johnson, who was monitoring the peak for activity that Sunday morning. Tragically, Johnston was killed in the sudden, violent eruption seconds after he got off the famous radio call to his supervisors: "Vancouver! This is it!" Seconds later, the ridge and everything on it was destroyed by the force of the eruption, which scientists have compared to the blast of an atomic bomb.

Then, in October 2004, ominous rumblings once again were noticed near the mountain, including the tell-tale "harmonic tremors." The 1980 eruption had had one important result: in the intervening quarter century, St. Helens had been outfitted with an elaborate array of seismic sensors, GPS devices and other sophisticated instruments that makes it the most closely watched volcano in the world. Small explosions were detected along with shallow earthquakes, and the steam eruptions were observed venting near the lava dome. On October 3, the USGS warned that an eruption was imminent.


Only minor eruptive activity has taken place at St. Helens in the intervening 6 months, although the mountain remains sufficiently unpredictable that the USGS will not allow the reopening of the Johnston Observatory. In January, the biggest eruption since October 2004 had scientists once again on the alert. Since activity began last fall, a bulging, oblong new lava dome has been rapidly growing inside the crater, at present reaching an altitude of almost 400 feet, with slopes as steep as 50-degrees. The USGS notes that at this present rate of growth, the dome will rebuild the mountain to it's pre-1980 level--almost 10,000 feet--as quickly as a decade.

As recently as early March 2005, USGS scientist warned that the ongoing activity could intensify suddenly or with little warning. and produce explosions that cause hazardous conditions within several miles of the crater and farther downwind. Small lahars (mudslides and debris flows) could suddenly descend the Toutle River if triggered by heavy rain or by interaction of hot rocks with snow and ice. The USGS remains on a high state of vigilance as it closely monitors the volcano's activity for signs of dangerous events.

Clearly, St. Helens demonstrates that the Earth is a work in progress, and offers a window into the complex geological processes that constantly alter the surface of our planet. In fact, volcanologist John Pallister of the Cascades Volcano Observatory, noted that one of the most predictable things about Mount St. Helens is its unpredictability.


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