Mount St. Helens lets off steam
MOUNT ST. HELENS, Wash. — A new column of steam emerged from Mount St. Helens on Sunday, a lazy plume that rose from the crater for several hours and reminded scientists of the volcano’s dome-building activity 20 years ago.
“It’s a view very, very reminiscent of the years in the 1980s during dome-building and a few years after when the system was hot and water was being heated and vapor was rising and steam clouds were forming,” said Willie Scott, a geologist with the U.S. Geological Survey.
The billow of steam rose from the south side of the volcano’s crater at dawn Sunday from the area where a large upwelling of rock has been growing rapidly.
From an airplane, a thick crooked plume of steam could be seen drifting at least 500 feet above the rim Sunday afternoon, dissipating a mile south of the 8,364-foot volcano.
Scientists believe the steam was created when part of the bubble on the south side of the dome broke off, taking some of the glacier with it. The ice melted, the water seeped down and that most likely caused the steam, said USGS geologist John Pallister.
The bubble of rock has risen to at least 330 feet since scientists first spotted it Sept. 30, and has become almost as tall as the dome’s 1,000-foot summit, said Pallister.
Scientists said Sunday’s steam cloud had no new ash but may have included some old ash from the 1980s.
Scott described the emission as a “very lazy conductive rise of this warm, moist air,” unlike previous weeks’ bursts characterized by more vigorous jetting that threw up ash, large pieces of rock and glacier ice.
Scientists made helicopter flights to collect gas-level samples and get a better look inside the crater on Sunday.
There had been an increase in earthquake activity over the past two days, with quakes of magnitude 2.4 occurring every two minutes. By Sunday afternoon, however, earthquakes were less frequent and weaker.
“What has been peculiar about these earthquakes is that there seems to be a disproportionate number of them that are uniform in size,” said seismologist Tony Qamar at the University of Washington’s seismic lab in Seattle.
It indicates that pressurization of the system is very uniform, which may suggest magma is constantly moving up into the system, he said. “The pressure will build up, the rock will break, and then you’ll get an earthquake.”
Scientists cannot say exactly where the magma is, however.
Seismicity had picked up steadily in recent days and by Saturday levels were equal to or higher than the Oct. 5 steam and ash eruption that sent a thick gray cloud thousands of feet in the air and dusted some areas northeast of the volcano with gritty ash.
The level alert remained at “volcano advisory” Sunday. Scientists have said an eruption would have to be imminent or occurring to raise the alert.
Activity is expected to ebb and flow, and the most likely scenario now is weeks or months of occasional steam blasts and possibly some eruptions of fresh volcanic rock.
Thousands of small earthquakes have shaken the peak in the Cascade Range since Sept. 23. The volcano spewed clouds of steam mixed with small amounts of old volcanic ash each day from Oct. 1 through Oct. 5.
Activity later diminished and the alert level was lowered Oct. 6. The downgrade indicated the probability of a life-threatening eruption had decreased significantly since Oct. 2, when thousands of people were evacuated from areas around the mountain.
Officials have cautioned, however, that an eruption still could occur with very little warning.
Geologists do not anticipate anything similar to the May 18, 1980, blast that killed 57 people, blew 1,300 feet off the top of the peak and paralyzed much of the inland Pacific Northwest with gritty volcanic ash.