Friday, May 18, 2007

The two debris-darkened arms of the glacier at Mount St. Helens drape around the lava dome that erupted from 1980 to 1986. This photograph was taken from the north this week. (DAVE OLSON/The Columbian)

Twenty-seven years after a massive eruption obliterated its summit, Southwest Washington's celebrity volcano is refashioning itself with a new look.

Visitors returning this week to the Johns­ton Ridge Observatory will notice a change since Mount St. Helens' main visitor center closed for the season just six months ago: two debris-blackened arms of a glacier set against the snow-covered crater floor.

Mount St. Helens' wraparound glacier has been uplifted, deformed and shoved out of the way by the eruption that began in the fall of 2004. Yet despite the massive intrusion of hot rock, scientists figure the glacier has lost only about a quarter of its pre-2004 volume.

"The ice is quite resilient," said Carolyn Driedger, a scientist with the U.S. Geological Survey in Vancouver. "Glaciers are quite resilient."

This particular glacier accumulated serenely over 18 years. Nurtured by snow and insulated by falling debris, the glacier built up to a thickness of 600 feet in the shaded void between an 876-foot-tall lava dome that emerged in the 1980s and the rounded crater wall rising more than 2,000 feet.

The new lava dome continues to grow by a rate of a pickup-truck-load every few seconds, with the last detailed scientific measurement on Dec. 6 estimating a total volume of about 118 million cubic yards, or enough to fill the Rose Garden arena more than 158 times. The multiheaded muffin-shaped dome leaves the glacier only one place to go: downhill.

The glacier's west arm, looming 60 to 130 feet in height at its edge, is plowing down the crater at about 3 feet a day.

From Johnston Ridge, the two arms appear to be reaching toward each other around the lava domes. In fact, although the arms are still about 400 feet apart, scientists say they could come together this year.

"They are moving closer together," said Tom Pierson, a USGS scientist in Vancouver.

Peter Frenzen, scientist for the Mount St. Helens National Volcanic Monument, is amazed by the interplay between fire and ice.

"You would have thought it would melt more of the glacier than it has," he said.

The hottest interior portions of the lava dome appear to be insulated by cooler outer layers, minimizing the amount of melting taking place at the glacier.

Instead, Driedger said, scientists will have the rare opportunity to watch a glacier form and migrate within the scope of human time.

"The eruption of lava through a glacier is a unique situation on Earth," according to a USGS summary of activity at Mount St. Helens.

Today is the anniversary of the day that 57 people died when a massive, 9-hour-long eruption turned day into night across Eastern Washington.

Triggered by the biggest landslide in history, the eruption exposed a gas-charged reservoir of magma that leveled 230 square miles of forest and expelled a 15-mile-high plume of ash that eventually circled the globe.

- The high point of the present lava dome is 1,155 feet above the crater floor - comparable to the height of the Empire State Building. Lava spines reached even higher last summer, but the dome lost 150 feet of height in subsequent rockfalls.

- The glacier's east arm is about 790 feet wide and 4,900 feet long.

- The west arm is about 1,050 feet wide and 8,530 feet long.

- The west arm of the glacier is bearing down on a U.S. Geological Survey seismic station about 200 feet away from the oncoming toe.

- The area of the glacier amounts to about a fifth of the glaciated terrain that existed on Mount St. Helens before May 18, 1980.

- The glacier covers about a third of a square mile, twice as much as White River Glacier covers on the south side of Mount Hood. The glacier is the newest to form in North America.

*NOTE: The state of Washington and the federal government differ over the glacier's official name. Federal cartographers recognize it as "Crater Glacier," while state maps show it as "Tulutson," the Cowlitz Indian Tribe's word for ice.

SOURCE: U.S. Geological Survey, David A. Johnston Cascades Volcano Observatory.