Wednesday, April 11, 2007

The Oregonian

The lava dome growing on Mount St. Helens has muscled the surrounding glacier, shaping the ice into two arms that are reaching farther down the crater's steep slope.

In a recent flight over the volcano, scientists with the U.S. Geological Survey's Cascades Volcano Observatory discovered the glacier has stretched out dramatically since last fall.

"Both of the glacier's snouts are advancing," said Joe Walder, a glacier expert with the observatory. "I expect that by this same time next year they will have merged."

Walder estimates that the glacier's arms, which are being shoved down the east and west sides of the crater rim, are separated by about the length of a football field.

In coming weeks, he and his colleagues hope to measure how far and how fast the arms have advanced.

A spine of lava split the nearly 700-foot-thick glacier in two soon after the volcano began the latest eruption, which has continued since October 2004. The spreading dome is squeezing the glacier against the crater wall, forcing it higher and shoving the arms northward.

John Pallister, an observatory geologist who has flown over the crater in the past two weeks, says the glacier's arms are "the first thing that catches your eye. I said, 'Wow, they have really moved over the past few months.' They're getting very impressive."

Pallister said the east arm appears to have moved farther than the west.

Glaciers always have been natural features on Mount St. Helens, but the massive May 18, 1980, eruption destroyed 70 percent of the peak's 13 glaciers. The new glacier began to develop inside the newly formed crater a couple of years after the eruption. The steep crater walls shaded the snow, ice and rock that had accumulated in a horseshoe shape around the lava dome.

Despite being deformed in the current eruption, the glacier is proving tough, easing initial concerns that the lava dome might cause it to melt rapidly and send floods down the North Fork Toutle River. The ice is protected by rock shed off the crater wall; the rock makes up about one-third of the glacier. Only about 10 percent of the glacier has been lost during the ongoing eruption.

Walder said it will be interesting to see what happens to the glacier now that its arms have moved out of the rim's shadow and are more exposed to the summer sun.

The glacier's growth has been an anomaly in the Cascades, where glaciers have been retreating for decades. It's giving scientists an unprecedented look at glacier formation and how it responds to exposure to a hot lava dome.

The glacier also is unusual in that it has two names. The Washington State Board on Geographic Names approved the name Tulutson, a Cowlitz tribal word for ice, in 2005. Last year, however, the U.S. Board on Geographic Names voted 8-4 to approve the name Crater Glacier, which observatory scientists preferred.

The result: The icy feature will be labeled Tulutson Glacier on Washington maps and Crater Glacier on federal maps.

The glacier could be devastated by a powerful eruption similar to 1980's blast, but there is no evidence that the volcano is building pressure as it continues to ooze about a half a cubic yard of lava into the crater every second. "This eruption could go on for a long time," Pallister said. "We don't know when it will stop, but low rates like this can trickle along for many years."

Walder, meanwhile, is keeping an eye on the glacier. "It's pretty much an oddball."