On Wednesday, the Geological Survey said the danger of a strong Mount St. Helens eruption had passed and downgraded its alert level from 3, the highest, to 2. (Related story: Scientists lower alert level)
"We no longer think an eruption is imminent in the sense of minutes or hours," geologist Willie Scott said.
But the volcano, which awoke Sept. 23 and erupted — if weakly — for the first time in 18 years Friday, was far from back to sleep and could keep venting steam and ash for several weeks, scientists said.
And Rainier is never far from their thoughts. More ice and snow cover its big dome than all the other Cascades volcanoes combined. So a big eruption would trigger gigantic debris flows — "more like a wall of wet concrete that nothing can stop," Wynn said — plus enormous snow and ice surges all the way to Puget Sound.
"The more ice, the more danger," he said. "Water really lubricates the flow and makes the distance it can cover far greater."
Alarms at Rainier
Residents of nearby towns would have less than an hour to get to high ground and watch their homes be swept away. Greater Seattle wouldn't be spared. Geologists have discovered, for instance, that Tacoma's port sits on a debris flow from the eruption five centuries ago.
That one blew off the east side of the mountaintop, the side pointing away from Seattle, but still spilled around the other side and into what are now densely populated areas.
What scares scientists today is the threat of a big one that blows off Rainier's west side. It's why the government has spent millions of dollars in recent years installing alarms around the volcano.
Mount Hood near Portland, Ore., hovers over 2 million people.
It hasn't blown since just before Lewis and Clark arrived in 1805, but recently swarms of small earthquakes have rumbled inside the 11,239-foot peak. A major eruption from Hood could threaten Portland's water supply if sediment flows reached the Sandy River, Wynn said.
The 1,000-mile-long Cascade chain is part of a vast loop of volcanoes, called the "Ring of Fire," that runs along the Pacific rim, from New Zealand up to Japan, along Alaska's Aleutian Islands and down the Pacific coast of Central and South America.
Three-fourths of the world's 600 active volcanoes sit on the ring.
The USA has 50 active volcanoes. St. Helens is the Cascades' most active member because of its location astride two of the gigantic plates that make up the Earth's crust, plates that constantly slide and bang into each other.
A vent for heat
Think of volcanoes as Earth's heat outlets. Volcanoes tend to erupt where one plate slides under another. Gas-rich molten rock called magma has a way to escape the earth's core.
Mount St. Helens is more active than other volcanoes because it lies along an especially weak area of crust.
But eruptions seen over a lifetime lack context. Mount St. Helens' 1980 calamity was "fairly small change in its own history," Wynn said. Three eruptions in the 14th century were all much larger.
An ancient eruption in what's now Yellowstone National Park — a "super volcano" — deposited several hundred feet of ash as far away as Colorado Springs.
Other Cascades volcanoes, such as 14,161-foot Mount Shasta in northern California, are considered low risks to erupt. Geologists believe Shasta, the chain's second-highest peak, blows about once every 600 years.
But don't expect the tumult inside Mount St. Helens to set off other volcanoes in the Cascades.
Wow, it is so beautiful view.