For Now, Mount St. Helens Is Slumbering But Danger Grows; Meanwhile, Mount Rainier Moves Up To No. 1 On The Volcano Hazard List

It occasionally belches a cloud of superheated steam, but for the most part, Mount St. Helens has been very quiet.

In fact, October marks the 10th anniversary since the mountain’s last eruption.

“At the moment, there is nothing to suggest any imminent eruptive activity at Mount St. Helens,” said Ed Wolfe, a volcanologist at the Cascades Volcano Observatory in Vancouver, Wash.

It has been so tame that fellow volcanic peak Mount Rainier - because of its potential to send giant mudflows cascading down populated valleys - has been moved up to No. 1 on the volcano hazard list.

Mount St. Helens’ most destructive blowup occurred May 18, 1980, when 57 people were killed and 230 square miles of forest were leveled. The eruption sent a cloud of ash circling the globe and caused more than $1 billion in damage and cleanup costs.

“A big blast and landslide are unlikely and there is less ice and snow available (on Mount St. Helens’ flanks) to generate lahars (mudflows) as there were in 1980. So for the time being, it is not as threatening,” Wolfe said.

But like many other naturally occurring phenomena, the volcano’s lack of activity is nothing to be complacent about. The volcano is continuing to grow, slowly heading for another eruption.

Slow-moving lava continuously is making its way to the surface through a pipelike conduit. There, it cools, contracts and hardens, clogging the volcano’s outlets and making it likely that the next eruption will be more violent than the eruptions that have occurred since the May 18, 1980, blast, Wolfe said.

“The next batch of magma that reaches the surface will have to break its way through,” causing tremendous pyroclastic flows of gas and pumice as well as towers of sky-bound ash, he said.

The mountain’s lava dome, now 1,000 feet high, would be blown apart.

Also, a new danger in the form of almost 70 million cubic yards of snow and ice is taking shape.

The mixture has accumulated in the shaded back portion of the Mount St. Helens crater in the last 10 years - enough trapped water to fill nearby Castle Lake nearly twice.

Depending on the type of eruption and time of year, a blowup could melt the snow and ice and cause a large mudflow to cascade down the Toutle River valley, Wolfe said.

Although it doesn’t appear that the mudflow would flood cities on the Cowlitz River, the growing size of the snow and ice mass is posing a definite threat, said Tom Pierson of the U.S. Geological Survey.

The snow and ice are expected to double in size in the next 15 years, Pierson said.