Explosive Lessons of 25 Years Ago
Wednesday, May 18, 2005
MOUNT ST. HELENS NATIONAL VOLCANIC MONUMENT, Wash. -- Twenty-five years ago, the bulging north flank of this mountain fell away in the largest landslide in recorded history. Stripped of its rock-and-ice corset, the volcano was suddenly semi-naked, its seething innards exposed to a fine spring morning.
And then it blew.
In an explosion heard 690 miles away in Canada, an ash-laden, superheated version of hell exited the mountain laterally and rioted northward at hundreds of miles per hour. It obliterated nearly everything in its path for eight miles, sandblasting old-growth forests down to bedrock. As far as 19 miles from the volcano, large evergreens were mowed down like grass. The lateral blast was followed by a vertical explosion of ash, enough to cover a football-field-size mound 150 miles high. The ash fell in measurable amounts in 11 states and soon circled Earth. Finally, mudflows overwhelmed local rivers, bullying their way down to the Columbia, where for weeks they blocked shipping lanes.
It was the most destructive eruption in U.S. history, and it killed 57 people -- incinerating a few, mummifying some, crushing, drowning or asphyxiating the rest. With the exception of one volcano scientist, a few loggers and Harry Truman, an octogenarian innkeeper who refused to leave the mountain, most of those who died had no compelling reason to be near the mountain. They died as volcano tourists.
Mount St. Helens is now wired so scientists and public safety officials can respond immediately to signs of trouble. These instruments have come in handy, as the volcano has awakened in recent months after 18 years of quiescence. It is energetically building itself a new lava dome and periodically belching great plumes of ash.
Owing to the big blow in 1980, careful attention is being paid to some of the volcano's older but still active cousins in the Cascade Range, two of which are near major population centers. Mudslides from Mount Rainier, which is far larger than St. Helens and much closer to Seattle and Tacoma, are regarded as such a serious threat that volcano evacuation routes have been established and schoolchildren near Rainier are regularly drilled in the art of running for high ground.
The eruption of Mount St. Helens -- filmed and photographed as it occurred -- occasioned new insights into how volcanoes work. The most important lesson learned here, according to scientists at the U.S. Geological Survey, is that volcanoes, before they explode, tend to fall apart.
"The reality that volcanoes fall apart was imprinted on all our brains in 1980," said Seth Moran, a survey seismologist at the Cascades Volcano Observatory.
Researchers have traveled to volcanoes around the world, evaluated the rubble pattern from old eruptions and concluded that Mount St. Helens, by the self-destructive standards of its peers, behaved rather typically.
The blast zone has also become an ecological laboratory where researchers have overturned conventional wisdom about how lakes, meadows and forests recover from a catastrophic natural disturbance.
"In 1980, we envisioned the recovery as a linear and predictable process," said Virginia Dale, a plant ecologist who was 28 and finishing graduate work at the University of Washington when the mountain erupted. "Now, that has all been thrown out the window."