WEST COAST Mount St. Helens belches steam, ash

The small eruption punched a hole in the glacial ice atop the mountain.
WASHINGTON POST
SEATTLE -- On Friday, after a week of steadily increasing seismic rumbling, Mount St. Helens burped a tall column of steam and ash that officials said was probably not a precursor to a large sustained eruption from the most active volcano on the West Coast.
The volcano is being closely monitored in part because of its cataclysmic explosion in 1980. The explosion killed 57 people, triggered the largest landslide in recorded history and blew 520 million tons of ash eastward across the United States.
The plume from Friday's 24-minute noontime eruption rose 10,000 feet before drifting away in light winds on a spectacularly clear autumn day. No injuries or damage to property were reported.
Seismic activity dips
When the eruption ended, government monitoring instruments showed a sharp decrease in the seismic activity that in recent days had been registering as many as four small earthquakes per minute on the mountain, located in a sparsely populated area of southwest Washington.
"This was a relatively small eruption," said John Major, a hydrologist with the U.S. Geological Survey. He said USGS observers near the volcano reported that no molten rock flowed from the point in the mountain's lava dome where the steam vented.
Speaking at a news conference, Major said the eruption appeared to have punched a hole about 100 feet in diameter in the glacial ice that covers part of the mountain's horseshoe-shaped dome. He said there was a small increase in melting ice and snow off the volcano but no reported mudflows, or lahars, which historically have been damaging consequences of volcanic eruptions in the Cascade Range.
After the 1980 eruption, a lahar traveled 50 miles from Mount St. Helens, ripping out bridges and destroying homes.
Small in comparison
In comparison, Friday's eruption was a "hiccup," USGS geologist Tom Pierson told reporters.
"This is exactly the kind of event we have been talking about and anticipating," Major said. He noted there is no evidence that a major flow of gas-rich molten rock, which could trigger a sustained eruption, has ascended from its known location seven miles underground to the top of the mountain.
Absent such a flow of molten rock, USGS scientists have said it is unlikely that recent increases in seismic activity on Mount St. Helens will result in a significant eruption that could endanger people or property outside the immediate vicinity.
Major compared Friday's "small explosive eruption" to the activity that came to be regarded as normal in the six years after the 1980 eruption.
In those years after Mount St. Helens literally blew its head off, more than a dozen lava eruptions built a rock dome inside the mountain's crater.