Life at Mt. St. Helens
On May 18, 1980, Mount St. Helens lost 1,314 feet of elevation. In the largest landslide in recorded history, the top and north side of the mountain rolled down into the surrounding landscape. A huge bulge of magma burst sideways through the dome and released a hot, ash- and rock-filled wind that tore through the forest at 350 miles per hour.
The blast scorched and ripped up surrounding trees, but no fires started because there was no oxygen. The landslide dammed streams and rivers, creating many new lakes, and left behind whole chunks of the mountain on the landscape. The extreme heat from the eruption melted snow and ice, creating enormous mud flows that took out buildings and bridges. Hundreds of millions of tons of ash were released that day; a vertical column of ash reached fifteen miles up into the atmosphere. 250 square miles of surrounding land were damaged.
Such catastrophes make people think about luck. I was talking with a retired seismologist recently at the Johnston Ridge Observatory, which overlooks the ruptured north side of the mountain. He told me that there was a party in town the night before the blast that all the scientists (except the famous Dave Johnston) attended. Otherwise more of them probably would have been in the â€œred zone.â€ He himself had left the Mt. St. Helens area a week before the eruption to study volcanoes in Hawaii.
The ecological recovery of the area has been partly a matter of luck, too. Some organisms were safe, while others had no chance. Stream-dwelling fish were obliterated, overwhelmed by the toxic mud and pumice flows. Migratory salmon, however, were still out in the ocean at this time of year and so were not affected. Fish in frozen lakes were protected by the covering of ice. Large mammals and birds all perished, unable to flee fast enough. But many small nocturnal mammals were sleeping in their underground burrows during the blast, which occurred in the morning. Still-hibernating amphibians and reptiles were also safely burrowed.
The 1980 eruption has given biologists a unique opportunity to study how luck interacts with muck, madness with method, to regenerate an ecosystem. In many ways it is like watching something come out of nothing, like watching life emerge on a barren planet. How it has played out in the last 26 years does not follow any simple model of ecological succession.
On March 18, Spirit Lake was filled in with the avalanche of earth and lava rock, and covered with blown-down trees. No life survived in the lake. But after the work of aerobic and anaerobic bacteria, and the fertilization provided by all the blown-down trees, the lake has been colonized by phytoplankton, algae, insects and amphibians, and is thriving.
On land, things are a lot slower-going. Nutrient-poor volcanic material covers the land where soil used to be. It will be a long time before the forests recover fully. The best places are steep slopes, where erosion uncovered surviving plants and opened the soil for pioneer species like nitrogen-fixing lupine. These plants attract insects and trap windblown seeds. A little clump of life called a “hotspot” forms. When these hotspots enlarge and knit together, the land ecosystem will become stronger. Large scale tree replantings are also contributing to recovery.
At the Mt. St. Helens Visitor Center at Silver Lake, you can see a cross-section of a Doug Fir that was taken down in the 1980 blast, but is thought to have survived the much-worse 1480 blast. You can read the extreme stress in its late 1400s growth rings. Change is the norm for Mt. St. Helens; the volcano became active again exactly two years ago this month. It is fascinating to watch life struggle to emerge from land that, according to Jimmy Carter in 1980, looked more rugged than a moonscape.