Mt. Saint Helens, a spectacular volcanic peak 50 miles northeast of Portland in the Cascade range, is shaking. The 9,677-foot mountain's symmetrical beauty often is compared to Japan's Fujiyama. With Mt. Hood and Mt. Adams, it is part of the grand, snow-capped scene in southwest Washington and northwest Oregon. But Saint Helens is trembling with a "swarm" of earthquakes that started March 20.
The intensity and frequency of the tremors, centered within three miles of the peak, has increased dramatically. Several shocks have registered over 4.0 on the Richter scale; one hit 4.5 on March 25. Frequency has increased to more than 40 per hour. Scientists monitoring the seismic activity are speculating on the possibility of a major volcanic eruption.
The Cascade Range was the scene of the most recent volcanic activity in the United States, outside of Alaska and Hawaii. The last eruption of Mt. Saint Helens was in 1857. But in northern Washington Mt. Baker, which erupted in 1870 , has been showing signs of action over the past few years. Mt. Rainier, kingpin of the Cascade Range, also erupted in 1870, and Mt. Lassen, at the southern end of the Cascades in northern California, put on a spectacular display that started in 1914 and didn't end until 1921.
Could Mt. St. Helens put on such a show? It could. A US Geological Survey study in 1978 pinpointed St. Helens as "the most explosive mountain in the US outside of Alaska and Hawaii."
The earthquake "swarm" activity has centered in the mountain and has not even been felt in the village of Cougar, Wash., 12 miles from the mountaintop. Scientists can't say whether the quakes portend a volcanic eruption. No Cascade volcanoes have erupted since seismic stations were set up on the mountains about 10 years ago.
Steve Malone, a University of Washington seismologist, says: "We know the mountain will erupt again, but we don't know when." The 1978 Geological Survey report predicted a St. Helens eruption within 100 years and "perhaps even before the end of the century."
Judy Terreberry, spokeswoman for the university's geophysical program, points out that the swarm activitiy is typical of what happens just before a volcano erupts, but that it does not necessarily mean it is going to blow. Volcanologists say an eruption would normally be preceded by venting activity. Mt. St. Helens has been emitting steam from some vents for the past five years, but there have been no real ventings observed through March 25.
When Mt. Lassen last erupted, it leveled a vast forest of virgin timber and spilled lava down the beds of Lost and Hat Creeks. But the area was unpopulated. The slopes of St. Helens are virtually unpopulated also, but recreationists, skiers, and climbers have already been cleared out because of quake-triggered avalanches.
US Forest Service officials March 25 recommended that residents near the foot of the mountain be evacuated.
Geologists say a major St. Helens lava flow could cause flooding of the Toutle and Cowlitz Rivers and could affect the flow of the Columbia. Airborne pumice and other volcanic debris could set off forest fires, block roads, and contaminate water supplies. It is believed that, barring a cataclysmic accident , there would be sufficent warning to allow evacuation of populated areas that might be threatened. Mt. St. Helens is wholly within the Gifford Pinchot National Forest.
The volcanic activity in the Cascades is not being watched simply because of its destructive potential. The mountain range is being studied as a potentially vast geothermal pool that could be a significant factor in meeting the region's energy needs.