SEATTLE – The flurry of earthquakes at Mount St. Helens (search) intensified further Thursday, and one scientist put the chance of a small eruption happening in the next few days at 70 percent.
Jeff Wynn, chief scientist at the U.S. Geologic Survey's (search) Cascade Volcano Observatory (search) in Vancouver, Wash., said tiny quakes were happening three or four times a minute. Larger quakes, with magnitudes of 3 to 3.3, were happening every three or four minutes, he said.
New measurements show the 975-foot lava dome in the volcano's crater has moved 2 1/2 inches to the north since Monday, Wynn said.
"Imagine taking a 1,000-foot-high pile of rocks and moving it 2 1/2 inches. For a geologist, that's a lot of energy," Wynn said.
Wynn estimated there was a 70 percent chance the activity will result in an eruption.
Scientists did not expect anything like the mountain's devastating eruption in 1980, which killed 57 people and coated towns 250 miles away with ash. On Wednesday, they warned that a small or moderate blast from the southwest Washington mountain could spew ash and rock as far as three miles from the 8,364-foot peak.
Scientists planned to fly over the volcano again Thursday to test for gasses that could indicate the presence of magma moving beneath the volcano.
Few people live near the mountain, which is in a national forest about 100 miles south of Seattle. The closest structure is the Johnston Ridge Observatory (search), about five miles from the crater.
The heightened alert has drawn a throng of sightseers to observation areas. Dawn Smith, co-owner of Eco Park Resort west of the mountain, told The News Tribune of Tacoma, "It's just been crazy the past couple of days."
A sign in front of her business reads, "Here we go again."
The Geological Survey raised the mountain's eruption advisory from Level 2 to Level 3 out of a possible 4 on Wednesday, prompting officials to begin notifying various state and federal agencies of a possible eruption. The USGS also has asked the National Weather Service (search) to be ready to track an ash plume with its radar.
In addition, scientists called off a plan to have two researchers study water rushing from the crater's north face for signs of magma. A plane was still able to fly over the crater Wednesday to collect gas samples. Negligible amounts of volcanic gas were found.
"An aircraft can move ... out of the way fast," Wynn said. "We don't want anyone in there on foot."
The USGS has been monitoring St. Helens closely since Sept. 23, when swarms of tiny earthquakes were first recorded. On Sunday, scientists issued a notice of volcanic unrest, closing the crater and upper flanks of the volcano to hikers and climbers.
Scientists said they believe the seismic activity is being caused by pressure from a reservoir of molten rock a little more than a mile below the crater. That magma apparently rose from a depth of about six miles in 1998, but never reached the surface, Wynn said.
The mountain's eruption on May 18, 1980, blasted away its top 1,300 feet, spawned mudflows that choked the Columbia River shipping channel, leveled hundreds of square miles of forest and paralyzed towns and cities more than 250 miles to the east with volcanic ash.