While earthquakes, steam and magma are getting all the attention on Mount St. Helens these days, the volcano’s most unique feature could be the icy epitome of slow motion that has sprouted on its flanks in the last two decades: its glacier.
The 1980 eruption that blew the top off Mount St. Helens also destroyed its 13 glaciers, but by 1982, the crater floor had cooled enough to allow snow to begin to stick. Now, even as the volcano stirs to life, the nation’s newest glacier is growing between the lava dome and the crater’s south wall.
At a time when most of the nation’s glaciers are receding, this one has advanced as much as 135 feet annually, flowing downhill toward the blasted north edge of the crater like a muffler draped around the neck of the lava dome.
“It’s the only growing glacier in the contiguous United States,” said U.S. Geological Survey hydrologist Steve Schilling at the Cascades Volcano Observatory in Vancouver, Wash.
There are two reasons the 8,364-foot volcano is a good incubator for the fledging glacier: the crater’s walls have protected the snow, preventing it from melting year to year, and rockfall from the crater walls and dome provides insulation, sometimes several feet thick. Even volcanic ash can serve as insulation for a glacier.
“A cross section of the glacier would look like a layer cake,” said Schilling, who has been granted permits for his Mount St. Helens research.
The glacier is 3,500 feet wide between the south side of the lava dome and the crater wall. Some parts are 600 feet deep, although the average is 325.
Scientists are calculating now how much water that translates to — having the rare advantage of pre-glacier maps of the crater floor at 3,000 feet.
At this stage, there’s not much concern the heat of the volcano will melt a significant amount of the glacier. A lake has formed in one of two explosive pits in the glacier and is now bubbling with carbon dioxide gas from the magma.
“It would have to break up an enormous amount of material,” Schilling said.
There are few comparable situations around the world but scientists are considering all of them, he added. Volcanos and glaciers coexist in Iceland and in Alaska.
Only one other volcano — in Katmai, Alaska — has hosted glaciers that have grown as quickly as this one, he said.
Recent activity at Mount St. Helens is lifting part of the glacier. Schilling said some layers are nearly vertical right now at a site on the southeast side of the dome where underground pressures are lifting ice and stone almost as high as the 1,000-foot-tall lava mound.
Researchers were trying to evaluate the glacier’s potential hazards before Mount St. Helens rumbled back to life Sept. 23 with thousands of small earthquakes, followed by intermittent venting of steam clouds sometimes mixed with ash. The south side of the lava dome has been rising for the past week, indicating molten rock within the volcano is moving upward.
The still-unnamed glacier contains about 120 million cubic meters of snow, ice and rock, Schilling said.