Volcano threat remains

Monday, Oct. 28, 1996 | 11:59 a.m.

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.

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

Mount St. Helens' most destructive blowup occurred on May 18, 1980, when 57 people were killed and 230 square miles of forest were leveled. The pressure of 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 the mountain's 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 naturally-occurring phenomena, the volcano's lack of activity is nothing to be complacent about.

The volcano is continuing to grow, slowly heading for a future eruption.

Slow-moving lava is continuously making its way to the surface through a pipe-like 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 18th blast, Wolfe said.

"The next batch of magma that reached 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 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 Valley, Wolfe said.

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

The field is expected to double in size in the next 15 years, Pierson said.