Ally_Kat
09-27-2004, 11:09 AM
St. Helens Quakes Could Lead To 'Hazardous Event'
September 26, 2004
SEATTLE - Seismologists believe there's an increased likelihood of a hazardous event at Mount St. Helens due to recent changes in the mountain's seismic activity, and a notice of volcanic unrest was issued Sunday afternoon by the U.S. Geological Survey.
"The key issue is a small explosion without warning. That would be the major event that we're worried about right now," said Willie Scott, a geologist with the USGS office in Vancouver.
The trails on the mountain are closed to climbing as a precaution. Existing climbing permits have been cancelled and Jacks Restaurant and Store has stopped issuing new permits.
Initially, hundreds of tiny earthquakes that began Thursday morning had slowly declined through Saturday.
By Sunday, however, the swarm had changed to include more than 10 larger earthquakes of magnitude 2 to 2.8, the most in a 24-hour period since the last dome-building eruption in October 1986, Scott said.
Some of the earthquakes suggest the involvement of pressurized fluids, such as water or steam, and perhaps magma.
The quakes have occurred at depths less than one mile below the lava dome within the mountain's crater.
The cause and outcome of the swarm was uncertain Sunday evening. A group of scientists planned to visit the mountain Monday to collect data.
"There's been no explosions, there's no outward sign that anything is occurring. This is all based on the pattern of earthquake activity that is occurring below the dome," said Scott.
Experts believe there is "an increased probability of explosions from the lava dome if the level of current unrest continues or escalates," USGS and the University of Washington Pacific Northwest Seismograph Network in Seattle said in a joint statement.
In the event of an explosion, Scott said the concern would be focused on the area within the crater and the flanks of the volcano. It's possible that a five-mile area primarily north of the volcano could receive flows of mud and rock debris. That portion of the mountain blew out during the 1980 eruption that left 57 people dead, devastating hundreds of square miles around the peak and spewing ash over much of the Northwest.
During the tiny earthquakes last week, UW seismology lab coordinator Bill Steele said heavy autumn rains may have caused groundwater to percolate into hot rock beneath the surface of the crater, which would increase pressure.
He said it would also raise the possibility of small steam explosions that could hurl rocks down within the crater.
A similar swarm of quakes in November 2001 and another in the summer of 1998 did not result in an eruption. However, the quakes could increase the likelihood of small rock slides from the 876-foot-tall lava dome within the mountain's crater.
In the 1986 eruption, magma reached the surface and added to the pile of lava on the crater floor.
For More Information:
St. Helens Info -- www.pnsn.org.
September 26, 2004
SEATTLE - Seismologists believe there's an increased likelihood of a hazardous event at Mount St. Helens due to recent changes in the mountain's seismic activity, and a notice of volcanic unrest was issued Sunday afternoon by the U.S. Geological Survey.
"The key issue is a small explosion without warning. That would be the major event that we're worried about right now," said Willie Scott, a geologist with the USGS office in Vancouver.
The trails on the mountain are closed to climbing as a precaution. Existing climbing permits have been cancelled and Jacks Restaurant and Store has stopped issuing new permits.
Initially, hundreds of tiny earthquakes that began Thursday morning had slowly declined through Saturday.
By Sunday, however, the swarm had changed to include more than 10 larger earthquakes of magnitude 2 to 2.8, the most in a 24-hour period since the last dome-building eruption in October 1986, Scott said.
Some of the earthquakes suggest the involvement of pressurized fluids, such as water or steam, and perhaps magma.
The quakes have occurred at depths less than one mile below the lava dome within the mountain's crater.
The cause and outcome of the swarm was uncertain Sunday evening. A group of scientists planned to visit the mountain Monday to collect data.
"There's been no explosions, there's no outward sign that anything is occurring. This is all based on the pattern of earthquake activity that is occurring below the dome," said Scott.
Experts believe there is "an increased probability of explosions from the lava dome if the level of current unrest continues or escalates," USGS and the University of Washington Pacific Northwest Seismograph Network in Seattle said in a joint statement.
In the event of an explosion, Scott said the concern would be focused on the area within the crater and the flanks of the volcano. It's possible that a five-mile area primarily north of the volcano could receive flows of mud and rock debris. That portion of the mountain blew out during the 1980 eruption that left 57 people dead, devastating hundreds of square miles around the peak and spewing ash over much of the Northwest.
During the tiny earthquakes last week, UW seismology lab coordinator Bill Steele said heavy autumn rains may have caused groundwater to percolate into hot rock beneath the surface of the crater, which would increase pressure.
He said it would also raise the possibility of small steam explosions that could hurl rocks down within the crater.
A similar swarm of quakes in November 2001 and another in the summer of 1998 did not result in an eruption. However, the quakes could increase the likelihood of small rock slides from the 876-foot-tall lava dome within the mountain's crater.
In the 1986 eruption, magma reached the surface and added to the pile of lava on the crater floor.
For More Information:
St. Helens Info -- www.pnsn.org.