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Mount Saint Helens


Mount Saint Helens heads Mt. St. Helens Sidebarthe volcano watch list in North America. It is the most active volcano in the Northwest, and one of the most closely monitored volcanoes in the world. "It's the volcano most likely to explode," says Bill Steele, director of the Seismic Monitoring Program at the University of Washington in Seattle.

Steele keeps tabs on the volcano through 11 seismographs, which are planted around the mountain's base and at the rim of the crater. These extremely sensitive instruments are connected to radio transmitters that send back a record of every "pop and gurgle" inside the volcano. Typically, they record a few small tremors each month.

Generally, scientists believe these tremors are produced by magma cooling several kilometers beneath the surface of the volcano. As magma cools, it settles and releases various gases, which escape upwards through the rock. These tremors, however, might also be a warning that magma is rising towards the surface. "We might have only a few months of warnings when the magma starts moving back into the mountain," says Steele. "I would not be surprised if we had another eruption in the next ten years."


Geologists had little warning before Mount Saint Helens's last major eruption. A small earthquake was recorded on March 20, 1980, followed a week later by a minor eruption. But the ground continued to tremble, and six weeks later, on Sunday, May 18, 1980, the mountain exploded in one of the most spectacular eruptions in recent memory.

Mount St. Helens erupts.The 200 mile-an-hour blast flattened trees 20 miles away, killed 57 people, and sheared 1,300 feet off the peak of the mountain, leaving a crater more than a mile wide. The north side of the volcano burst, letting lose a side-long flare of magma and burning gas that incinerated the surrounding region. One hundred and fifty square miles of prime old-growth forests were reduced to a wasteland of scorched timber buried under a thick layer of volcanic ash, where fires burned for weeks afterwards.

The blast also triggered the largest landslide in recorded history, sending ash and rocks, some the size of large buildings, tumbling across a 14 mile swatch of land. The landslide also spilled into Spirit Lake, sending millions of gallons of water surging down the mountain. This water picked up debris and created a mudflow, known as a lahar, which rushed down the mountain, wiping away bridges and roads. The lahar poured down Toutle Valley, jamming rivers, destroying homes, and blocking navigation as far away as the Columbia River.

The eruption also sent more than 540 million tons of volcanic ash raining down over 22,000 square miles, covering Montana, South Dakota, and Nebraska, and sending ash drifting as far away as Virginia. From space, the eruption initially took the shape of a giant mushroom cloud, signifying a blast 400 times more powerful than the atomic bomb that leveled Hiroshima.



Rebirth is the legacy of natural destruction, and life quickly returned to the scorched earth near Mount Saint Helens. The rapid regeneration surprised most scientists, who believed that the rebirth would occur in steady, regular stages. Instead, nature ran riot, led by dozens of organisms that had amazingly survived the devastation. Moles, tiny pocket gophers, and ants survived because they were buried when the explosion occured. And saplings and shurbs buried in the snow survived, while the taller trees were devastated.

The tiny pocket gophers turned into a major force for renewal. Their habitual digging into the soil mixed the sterile volcanic ash with the rich earth buried below. Deer mice, ants, and beetles also assisted in turning over the soil, allowing new plants, shrubs, and trees to take root quickly. Algae, plankton, and various freshwater crustaceans quickly appeared to recolonize the ash poisoned lakes in the area, followed soon after by frogs and salamanders.

Fireweed plantEven large animals quickly returned. Elk were seen on the mountain's west slopes within weeks of the eruption, and by the following summer, the hills near the volcano were covered with fireweed, a pink flowering plant whose seeds are carried like little parachutes on the wind. Grasses, plants, and trees quickly took root in the sterile ash, and after three years, the plant composition in the blast zone was similar to adjacent lands that had been recently logged.

The federal government moves more slowly than mother nature, but some 110,000 acres around the volcano were set aside in 1992 and turned into a park called the Mount Saint Helens National Volcanic Monument. A law was also passed that allowed nature to follow its own course in the park, permitting scientists to continue studying the cycles of natural regeneration.

The eruption has also generated an unexpected economic rebirth in the region. Mountain climbing to the summit of the volcano has been allowed since 1986. By the end of 1989, the park had hosted more than 1.5 million visitors. Today, the volcano continues to draw more than 600,000 visitors a year, and tourism has become a major economic engine for the region.

The last two decades have also witnessed 30 more small eruptions on the mountain, and molten rock continued to surface as late as 1986. Between 1980 and 1986, Mount Saint Helens built a lava dome about 1,000 feet high and 3,500 feet in diameter. The last significant eruption was in 1994.



-- By Micah Fink


 

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