When Mount St. Helens erupted on May 18, 1980 the mountain's top cascaded into the Toutle River Valley below. The massive landslide exposed molten rock and caused a powerful, laterally directed blast. This pyroclastic surge, consisting of rock fragments, highly charged gas and superheated steam, devastated almost 150,000 acres of privately owned, state and national forests. Following the eruption, mud flows and associated flooding caused additional, extensive damage to public and private property downstream on the Toutle and Cowlitz Rivers.
Weyerhaeuser Company, which has owned and managed the St. Helens Tree Farm since 1900, was the largest private landowner impacted by the eruption. Nearly 68,000 acres, about 14% of the Tree Farm, were devastated. In addition to the trees, Weyerhaeuser lost 3 logging camps, buildings, equipment and vehicles. In addition, 650 miles of roads, 19 bridges and 16 miles of railroad were buried in ash or washed away by mud flows that swept down the Toutle River.
Following a National Institute for Occupational Safety and Health study of the blast zone, Weyerhaeuser company and contract employees began harvest operations on September 15, 1980 to salvage the trees remaining after the May 18 eruption.
Quick action was necessary to avert disease and insect damage to the fallen timber. More than 1,000 people were involved, and during peak summer periods, more than 600 truckloads of salvaged logs were removed each day. By the completion of the recovery phase in November of 1982, 850 million board feet of timber were saved—enough lumber to build 85,000 three-bedroom homes.
Natural revegetation was visible within a month of the eruption. Fireweed, braken fern, thistle, groundsel and pearly everlasting are now common at elevations between 1,500 to 3,000 feet above sea level.
Natural vegetation in areas less than six miles from the mountain returned very slowly. Ash depths here ranged up to several feet and, in some cases, the soil was removed down to the bedrock during the explosive eruption. At these locations—with elevations between 3,000 and 5,000 feet—lupine, Indian paintbrush, alpine lily, fireweed and pearly everlasting dot the landscape.
Within four weeks of the eruption, Weyerhaeuser foresters and scientists planted research study plots to determine the effects of ash on reforestation. Based on these results, Weyerhaeuser scientists predicted normal survival and growth could be expected for conifer seedlings as long as the ash was scraped away so that the seedlings' roots could be placed directly in the underlying mineral ash.
Weyerhaeuser completed the reforestation of damaged areas on its St. Helens Tree Farm in June 1987. In total, 18.4 million trees were hand planted, one by one, on over 45,500 acres. Species planted were those that had grown in the area prior to the eruption: Douglas fir and noble fir with some lodgepole pine and black cottonwood.
Some of the trees that were planted during the first planting season of 1981 measured more than 45 feet in the summer 1998. Areas in the blast zone will be ready for thinning by the year 2000 with some final harvesting beginning in 2025. And the forest cycle will begin again.
Within the 150,000-acre eruption area, almost all the above-ground wildlife perished during the 1980 eruption. Biologists spent several years after the eruption monitoring the return and movement of animals within the blast zone. As a result of reforestation and the natural reestablishment of the plant communities, the eruption area is now densely covered with vegetation and provides year-round habitat for hundreds of elk which began migrating back in 1981. In 1989, through a cooperative effort between Weyerhaeuser, the Rocky Mountain Elk Foundation and the Washington Department of Wildlife, a total of 3,000 acres of grass-seeded mudflow was preserved as the Mount St Helens State Wildlife Area.
On August 26, 1982, Congress established the Mount St. Helens National Volcanic Monument, totaling more than 110,000 acres, which includes areas devastated by the 1980 eruption and areas of undamaged old-growth forest. The purpose of the monument is to allow natural processes to proceed unaided by humans and for public and scientific viewing, study and interpretations.
The Spirit Lake Memorial Highway exxtends 30 miles to viewpoints within the monument. Along the way, visitors have the opportunity to contrast the monument's natural regeneration with the Weyerhaeuser's vigorous regenerated forest, the result of early hand-planting of Douglas fir and noble fir trees.
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