Volcano’s lava flow into crater continues

VANCOUVER, Wash. – If lava continues to pile up inside the blasted crater of Mount St. Helens at the current rate, the volcano could rebuild its summit in about 10 years.

Geologists, however, say it’s unlikely the current furious lava production will continue.

But it’s possible the volcano will erupt sporadically over the next 20 to 50 years or more, and gradually regain its former height, said Willie Scott, a volcanologist with the U.S. Geological Survey’s Cascades Volcano Observatory in Vancouver, Wash.

“We’ve been having an eruption constantly for more than a month. Dome growth can go on for weeks, months, years or decades. The possibilities are endless,” Scott said Friday during a news conference at the observatory, about 50 miles south of the mountain.

The new dome and the uplifted floor beneath it now cover 70 acres and stand 750 feet high. That’s about as big as Seattle Center and as tall as the 55-story Washington Mutual Tower in downtown Seattle.

“It’s a big flat pancake thrusting a skyscraper up in the air,” geologist Tom Pierson said.

Scott noted that dangers increase as the lava dome gets taller. Unstable slopes can trigger mud flows or collapse into avalanches of hot rock and gas that could flow for miles. The weight of the dome could put pressure on underground magma, increasing the risk of explosive eruptions.

“Lava domes are notoriously unstable,” Scott said. And this is a rather unpredictable volcano. “It’s very important we monitor the situation closely.”

This year’s eruption pattern has been quite different from that of the 1980s, when the last dome-building eruptions occurred. Back then, molten rock pushed up in short bursts, followed by weeks or months of quiet.

Now, the lava just keeps coming, Scott said.

Scientists initially collected samples of the new rock in a bucket suspended from a helicopter. Early this month, they made quick forays onto the new dome, using hammers to break off chunks almost too hot to hold.

“You can actually put your hand on some of the youngest rock on Earth up there,” Scott said.

Analysis of crystals and minerals in the new rock suggests the magma is flowing from a chamber four to five miles below the surface, a journey that takes a week or less.

That explains why earthquake activity has dropped to tiny temblors at a recorded rate of one every minute, USGS seismologist Seth Moran said. The magma is flowing smoothly, with few obstacles that require major shaking.

But if the flow is clogged, pressure could build inside the system and trigger an explosive eruption. The type of lava is very similar to that produced in 1980, Scott pointed out.

“It’s the kind that could drive the large explosive eruptions that St. Helens is well-known for in the past,” Scott said.

Mount St. Helens has a long history of abrupt change, from pyroclastic flows to quiet dome-building to fierce explosions.