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St. Helens sprouts 300-foot lava plug

The new lava lobe inside Mount St. Helens’ crater has sprouted a piston-like protrusion the size of a 30-story building — glowing red at night.
Magma in the crater of Mount St. Helens glows red in this image taken from the Johnston Ridge Observatory, located about five miles north of the volcano in southwestern Washington sate. AP
/ Source: The Associated Press

The new lava lobe inside Mount St. Helens’ crater has sprouted a piston-like protrusion the size of a 30-story building — glowing red at night.

“The magma is pushing the plug upward. It’s going high in the sky,” said hydrologist Carolyn Driedger of the U.S. Geological Survey at the Cascades Volcano Observatory in Vancouver, about 50 miles from the southwestern Washington mountain.

One section of the new lobe has risen by 330 feet in the past nine days, Driedger said Friday. Exact dimensions are not yet known but will be determined from photos taken Thursday.

“It seems like every time you think you know what’s going on, (the volcano) twists and does something different,” said Jeff Wynn, chief scientist for volcano hazards at the observatory.

Two scientists flew into the crater by helicopter Thursday and landed beside the new structure, under strict orders to stay no longer than 10 minutes to collect samples, he said.

The new lobe, which began building last month, had grown to roughly the size of an aircraft carrier. Scientists described it as 900 feet long and 250 feet wide.

Magma, or molten rock, is reaching the surface at the rate of 7 to 8 cubic meters about — one large dump truck load — every second, Wynn said.

Like the old lava dome, formed in the six years after St. Helens’ devastating May 18, 1980, eruption, the new lobe is made of a type of volcanic rock called dacite, Wynn said. More than 63 percent silica, it tends to be sticky and viscous, unlike the free-flowing lava of Hawaii.

Temperatures on the new protrusion can spike as high as 1,200 degrees Fahrenheit.

The current dome-building began with intense seismic activity Sept. 23, which indicated magma was breaking through rock. Several steam eruptions followed, and geologists detected lava at the surface late Monday.

Large explosion possible, but unlikely
Gas-rich magma can cause explosive eruptions, but samples taken this week have detected little carbon dioxide or hydrogen sulfide, Neal said. There was no evidence, such as increasing earthquakes or ground deformation, to suggest pressure was building, she said.

So far this fall, the most visible bursts at St. Helens have involved steam and small amounts of ash as rainwater and glacier melt combined with hot rock in the crater of the 8,634-foot peak.

As the dome-building continues, it could produce small explosions with little warning, Neal said.

A large explosion is still possible, but is among the least likely scenarios, she said. Such a blast could send a column of steam and gritty ash tens of thousands of feet up and out, posing potential problems for airplanes and road traffic.

Trails within a five-mile radius of the peak remained closed, with the alert level at mid-range. The Forest Service, however, reopened some roads and trails near the mountain.

Mount St. Helens has been the most active volcano in the lower 48 states and Canada during the past 4,500 years. Its 1980 eruption hurled debris nearly 20 miles north, killed 57 people and paralyzed much of the Northwest with gritty, machine-clogging ash.