Mountain’s growth spurt slowing
SEATTLE – Growth of the new lava dome inside the crater of Mount St. Helens has gradually slowed and become less steady since it began in early October, scientists from the Cascade Volcano Observatory said Tuesday.
“The rate of dome growth has slowed since early October and the area in the crater that was deforming was (changing) much faster in early October than it is now,” U.S. Geological Survey research hydrologist Jon Major said in a telephone conference update.
Molten rock has been oozing out from the surface of the volcano’s crater since October, building a new lava dome that now has a total volume of 44 million cubic yards.
The new dome is about 45 percent the size of the old dome to the north, which formed during a similar period of activity in the 1980s, and has grown 350 feet taller than the old dome during the current eruptive phase.
Scientists provided an update from the Vancouver observatory, about 50 miles south of the peak, nine days after a small explosion at the north end of the new dome sent ash nearly two miles from the crater.
The Jan. 16 explosion destroyed a camera and some measuring equipment that had been placed in the crater two days earlier. The blast was on a similar scale to explosive events in early October, Major said.
In the 36 hours the equipment was functioning, it recorded the new dome grew 13 feet upward and about 23 feet to the south. Scientists said there was a spike of sulfur dioxide before the explosion.
“Right now we are being especially cautious and assessing whether this was an unusual event or if there will be repeats,” geologist John Pallister said. “But we are wanting to move ahead with instrumentation on the crater.”
Initially, the new lava dome switched between vertical growth and horizontal growth toward the southern edge of the volcano crater. Since December, the northern section of the new lava dome has continued its upward growth at about 33 feet per day.
The upward growth brings up concerns of possible collapse, Pallister said. In other volcanoes, a dome collapse can expose an interior with suppressed gases and produce some type of explosion with a significant ash cloud that could cause problems for aircraft flying around the mountain, he said.
But with Mount St. Helens, collapses thus far have produced small ash emissions, according toPallister.
The massive May 18, 1980, eruption of the volcano 100 miles south of Seattle blew the top 1,314 feet off the 9,677-foot peak, killed 57 people and covered the region with gritty ash.