Nearly two weeks after it first started rumbling and shaking, Mt. St Helens, the volcano 45 miles northeast of Portland, Ore., in southwest Washington State, is steadily stepping up the intensity of its spectacular show.
Since April 1, the mountain has spewed a tremendous volume of volcanic ash over a wide area, most of it blowing eastward, deeper into the Cascade Mountain range and on over the high plateau of eastern Oregon and Washington.
The volcano, the first to become active in the continental US since 1921, started its show March 20 with a "swarm" of earthquakes inside the mountain. Then there was steam venting, followed by eruptions of steam and gas and ejection of material that had accumulated in the "throat" of the volcano since its last eruption in 1857.
So far, there has not been what volcanologists classify as a major eruption. But Mt. St. Helens, its 9,677-foot cone clearly visible from Portland in clear weather, is following the classic script that could lead to a traditional volcanic blowout.
Scientists say that for a final volcanic climax to occur there would have to be sufficient molten material in the mountain and below it to push to the top or out through a vent lower down. Then the molten material could spill out and flow down the sides of Mt. St. Helens in the form of lava. Or it could take the form of a violent ash eruption.
Based on volcanic history, experts say, the mountain also could return to dormancy without much further activity, go on for months with periods of rumbling and spasmodic expulsion of old materials from the volcano throat, or erupt with a violent outpouring of new molten lava or ash or both.
Alexander McBirnie, volcanologist at the University of Oregon's Center for Volcanology, says: "This has not been an unusual eruption so far. This is a quite common way of behaving."
Beginning March 20, molten rock deep under the mountain triggered and continues to trigger earthquakes as it tries to push up and out the volcanic throat. If it clears a path it could spew out as lava or ash.
Donald Nichols, chief of geological engineering for the US Geological Survey in Denver, says: "If whatever is the driving force moving the magma upward is still there and increases, it could very well result in lava flows or in a very explosive ash-type eruption." He added, however, that activity could subside and the volcano could become dormant again.
Whatever happens, the show so far has been spectacular. Eruption viewing has varied from excellent on several clear days to completely blacked out on a number of others when the mountain has been shrouded in a deep cloud cover.
Two new craters have opened near the summit of the mountain, and it is expected that these eventually will be joined into one huge new opening. The symmetrical snow cone shape of the mountain already has been changed into a twin-peaked saddle formation. Falling ash has stained the eastern and southern flanks of the snowcapped peak, only to be covered by fresh snowfalls. Ash has been detected on the surface as far away as Moscow, Idaho, 300 miles to the east.
Wind shifts have dumped ash on Cougar, Wash., 12 miles southwest of the mountain, and ash has been drifting toward the Portland-Vancouver metropolitan area 40 to 45 miles to the southwest.
Giant plumes of steam, ash, and gas have billowed as high as 17,000 feet above the peak. Mud slides and avalanches as long as 1,000 feet have cascaded down Mt. St. Helens' flanks.
Meanwhile, national forest officials and state, county, and municipal authorities are trying to cope with crowds of sightseers attempting to get near the mountain.