Mount St. Helens is world's newest glacier

SEATTLE – Mount St. Helens' Crater Glacier continues to grow while most others around the world are shrinking.

Ray Yurkewycz perched on the rim of the Northwest's most restless volcano and marveled at the primordial forces at work.

Rocks and boulders sloughed off the crater walls, kicking up plumes of dust as they clattered down the near-vertical slopes. Steam rose from the twin magma domes formed after Mount St. Helens' cataclysmic eruption in 1980 and the quieter outburst that started in 2004.

But Yurkewycz, operations director for the nonprofit Mount St. Helens Institute, was focused less on the volcano's fiery past than its icy present. Few people realize, he said, that the hollowed-out crater where lava was flowing just a few years ago now holds the world's youngest glacier.

And if that's not surprising enough, the prosaically named Crater Glacier is also growing at a time when most glaciers around the globe are in rapid retreat.

"It's cascading down into this valley now," Yurkewycz said, pointing out a tongue of ice flowing over a rise and into a rubbly ravine. "It's only been in the last two years that it started doing that."

On the volcano's north side, where the 1980 blast scoured away all life, the U.S. Forest Service — which manages Mount St. Helens National Volcanic Monument — has long limited public access. Not only are the rugged upper slopes treacherous, but the area serves as an open-air laboratory for scientists tracking the ecosystem's recovery.

"Nothing about this glacier is typical," said USGS scientist Steve Schilling.

Before 1980, Mount St. Helens was a post card-perfect cone draped with about a dozen small glaciers. Most were obliterated or melted on May 18 of that year, when the mountain's north side collapsed, unleashing the biggest landslide ever recorded.

An explosive, lateral blast vaporized everything in a miles-long swath and leveled 230 square miles of forest. When the dust and ash settled, what was left was a horseshoe-shaped shell of a mountain with a few remnant snow fields clinging to its flanks.

But that shell provided a perfect nest to nurture a baby glacier.

Its northward orientation helped shield snow from the sun. A thick layer of loose, volcanic rock collected on the crater floor, providing an insulating barrier against volcanic heat rising from below. And when a magma dome began bulging upward — eventually growing nearly 900 feet high — it formed a sheltered niche along the crater's back wall where snow could pile up.

Normal snowfall alone can't account for the glacier's formation, though, said USGS geologist Dave Sherrod. An extra boost comes from the loads of snow and ice that slough into the crater off the rim and walls.

"It's as if you've doubled, tripled or quadrupled the amount of snow and ice accumulation in this small area," Sherrod said. "It's a fountain of youth as far as the glacier is concerned."

By 1988, a permanent snowfield more than 200 feet thick nestled in the crater. In 1996, the first crevasses appeared — evidence that the frozen mass was in motion and met the definition of a glacier.

But things really got weird in 2004. That's when the volcano sputtered back to life, intermittently spitting steam and oozing thick, pasty magma in a low-key eruption that lasted for several years. The magma quickly built a new dome taller than the Empire State Building, and it wedged between the old dome and the crater wall.

The USGS team held its breath, fearing the heat would liquefy the glacier and send water and mud rampaging through the valleys below. But the ice was so well insulated by its underlying rock layer that very little melted away.

The ice is about 650 feet thick in places, Sherrod said — deep enough to swallow the Space Needle.

Measured in a straight line from head to snout, the glacier is 1.25 miles long.