Mount St. Helens

A Volcano

Washington

August 12th, 1998

Washington State surely has its unique place in the United States. For several months a year, it is truly a paradise for everyone. What would you have? The big city atmosphere of Seattle, the Puget Sound, the Pacific Ocean, the big forests, even the mountains. Why, you would say, nothing more than California has to offer. Ah, but the heart of Washington State holds it’s uniqueness within the Cascade mountain range. Here lie the smallest of five major volcanic peaks in this wonderful state. Mount St. Helens, with an elevation of 9,677 feet (2,950 m) (before the eruption of May 18,1980) is unique in United States history. But I’m getting ahead of myself. We had driven up out of Oregon, looking for adventure in the great state of Washington. It was time for big trees, campfires, and a “get back to nature” experience. We had stopped at the Ike Kinswa state park outside of Mossyrock. The next day we took the long drive around route 12 and stopped at the Mt. St. Helens national park. The devastation was overpowering. As we wandered through the desolation we came across Ranger Paul Swanson who was about to give a talk and a walk through a section of park. He opened his presentation by asking us to back up to March 20, 1980. After a quiet period of 123 years, earthquake activity once again began under the Mt. St. Helen's volcano. Seven days later, on March 27, small phreatic (steam) explosions began. A "bulge" developed on the north side of Mt. St. Helens as magma pushed up within the peak. Angle and slope-distance measurements to the bulge indicated it was growing at a rate of up to five feet (1.5 m) per day. By May 17, part of the volcano's north side had been pushed upwards and outwards over 450 feet (135 m). On May 18, at 8:32 a.m. Pacific Daylight Time, a magnitude 5.1 earthquake shook Mt. St. Helens. The bulge and surrounding area slid away in a gigantic rockslide and debris avalanche, releasing pressure, and triggering a major pumice and ash eruption of the volcano. Thirteen hundred feet (400 m) of the peak collapsed or blew outwards. As a result, a debris avalanche filled 24 square miles (62 square Km) of the valley. 250 square miles (650 square km) of recreation, timber, and private lands were damaged by this lateral blast. An estimated 200 million cubic yards (150 million cubic meters) of material was deposited directly by lahars (volcanic mudflows) into the river channels. Fifty-seven people were killed or are still missing. For more than nine hours a vigorous plume of ash erupted, eventually reaching 12 to 15 miles (20-25 km) above sea level. The plume moved eastward at an average speed of 60 miles per hour (95 km/hr), with ash reaching Idaho by noon. By early May 19, the devastating eruption was over. After the May 18, 1980 eruption, Mount St. Helens' elevation was only 8364 feet (2,550 m) and the volcano had a one-mile-wide (1.5 km) horseshoe-shaped crater, seen here from the northwest. For weeks, volcanic ash covered the landscape around the volcano and for several hundred miles downwind to the east. Noticeable ash fell in eleven states. The total volume of ash (before its compaction by rainfall) was approximately 0.26 cubic mile (1.01 cubic km), or enough ash to cover a football field to a depth of 150 miles (240 km). The downed trees, over four billion board feet of usable timber, would have been enough to build 150,000 homes. The nearly 2/3 cubic miles (2.3 cubic km) of debris avalanche that slid from the volcano on May 18, is enough material to cover Washington, D.C. to a depth of 14 feet (4 m). The avalanche traveled approximately 15 miles (24 km) downstream at a velocity exceeding 150 miles per hour (240 km/hr). It left behind a hummocky deposit with an average thickness of 150 feet (45 m) and a maximum thickness of 600 feet (180 m). More than 200 homes and over 185 miles (300 km) of roads were destroyed by the 1980 lahars. During the May 18, 1980 eruption, at least 17 separate pyroclastic flows descended the flanks of Mt. St. Helens. Pyroclastic flows typically move at speeds of over 60 miles per hour (100 km/hr) and reach temperatures of over 800° Fahrenheit (400° Celsius). This was truly one of nature’s greatest destructive acts in North America. But like nature’s ability to destroy itself, it most assuredly will recreate itself. Just months after the fatal blast, the fireweed appeared. That resilient plant that sprouts after every northwestern forest fire. Those who, having not seen this destruction, and wishing to witness the carnage, will have to do so within the next few decades. Otherwise nature will have licked its wounds and recovered its devastation. Soon the land will again be covered with spruce, cedar and alder, and all signs except the gigantic crater will have vanished.

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