MOUNT ST. HELENS NATIONAL VOLCANIC MONUMENT (Reuters) - Mount St. Helens spewed steam and ash high into the skies above Washington on Friday as it awoke from years of slumber, but remained far below the scale of the catastrophic 1980 eruption that killed 57 people.
A plume rose in a column from the crater against the clear blue sky just after 12 p.m. PDT. The volcano, 100 miles south of Seattle, last erupted, without serious damage, in 1986.
Steam and ash blew upward for about 24 minutes to an altitude of 10,000 feet, and began dissipating an hour after the single explosion, said Jon Major, a U.S. Geological Survey (news - web sites) (USGS (news - web sites)) researcher at the Cascades Volcano Observatory in Vancouver, Washington.
The May 18, 1980, eruption caused 57 deaths, destroyed more than 200 homes and devastated hundreds of square miles of surrounding land. Ash from that outpouring billowed across North America, traveling as far east as Oklahoma.
Friday's explosion punched a hole in the glacier inside of the volcano's crater and spread black and gray debris across its icy surface. No lava or lahar -- mud flows -- spilled out of the horseshoe-shaped crater.
"Whatever triggered this event was not magma that reached the surface," Major said, adding that seismologists continued to track earthquakes for signs for more activity.
"If the seismicity starts to ramp back up and goes back to the levels we've seen prior to this event, then it is a harbinger that we are not finished yet," Major told reporters, "If the seismicity has essentially tailed off and goes back to background (levels) and doesn't come back up, perhaps this was a one-shot deal."
Geologists who were installing equipment in the crater of the volcano were safe, the USGS said.
AIR TRAFFIC DIVERTED
Wind was carrying the plume of steam and ash rising above Mount St. Helens northwest over uninhabited areas, said Peter Frenzen of the U.S. Forestry Service.
Since ash can damage and stall aircraft engines, nearby planes were diverted around the cloud, said Allen Kenitzer, spokesman at the Federal Aviation Administration (news - web sites).
Alaska Airlines canceled five flights out of Portland, Oregon, 50 miles south of the volcano, and diverted four flights to Seattle, but said it resumed normal operations two hours after the eruption.
The several hundred witnesses at the Johnston Ridge Observatory did not report hearing any loud explosions.
Earlier on Friday, government scientists reported that the lava dome created after the 1980 eruption had swollen slightly and that cracks appeared on the glacier inside the rumbling volcano's crater.
Recent activity, which started with a series of small earthquakes a week ago and a 2.5-inch shift in the lava dome's location, is happening within the horseshoe-shaped crater that formed after the eruption.
Seismologists said there was no connection between activity at Mount St. Helens and a strong earthquake near Parkfield, California, or a smaller series of quakes in Alaska earlier this week.
The violent 1980 eruption of Mount St. Helens reduced its summit from 9,677 feet to 8,364 feet.
In addition to the 1986 eruption of the mountain's lava dome, strong earthquakes were detected in 1989, when fresh magma entered the volcano's lava system.
A plume rose in a column from the crater against the clear blue sky just after 12 p.m. PDT. The volcano, 100 miles south of Seattle, last erupted, without serious damage, in 1986.
Steam and ash blew upward for about 24 minutes to an altitude of 10,000 feet, and began dissipating an hour after the single explosion, said Jon Major, a U.S. Geological Survey (news - web sites) (USGS (news - web sites)) researcher at the Cascades Volcano Observatory in Vancouver, Washington.
The May 18, 1980, eruption caused 57 deaths, destroyed more than 200 homes and devastated hundreds of square miles of surrounding land. Ash from that outpouring billowed across North America, traveling as far east as Oklahoma.
Friday's explosion punched a hole in the glacier inside of the volcano's crater and spread black and gray debris across its icy surface. No lava or lahar -- mud flows -- spilled out of the horseshoe-shaped crater.
"Whatever triggered this event was not magma that reached the surface," Major said, adding that seismologists continued to track earthquakes for signs for more activity.
"If the seismicity starts to ramp back up and goes back to the levels we've seen prior to this event, then it is a harbinger that we are not finished yet," Major told reporters, "If the seismicity has essentially tailed off and goes back to background (levels) and doesn't come back up, perhaps this was a one-shot deal."
Geologists who were installing equipment in the crater of the volcano were safe, the USGS said.
AIR TRAFFIC DIVERTED
Wind was carrying the plume of steam and ash rising above Mount St. Helens northwest over uninhabited areas, said Peter Frenzen of the U.S. Forestry Service.
Since ash can damage and stall aircraft engines, nearby planes were diverted around the cloud, said Allen Kenitzer, spokesman at the Federal Aviation Administration (news - web sites).
Alaska Airlines canceled five flights out of Portland, Oregon, 50 miles south of the volcano, and diverted four flights to Seattle, but said it resumed normal operations two hours after the eruption.
The several hundred witnesses at the Johnston Ridge Observatory did not report hearing any loud explosions.
Earlier on Friday, government scientists reported that the lava dome created after the 1980 eruption had swollen slightly and that cracks appeared on the glacier inside the rumbling volcano's crater.
Recent activity, which started with a series of small earthquakes a week ago and a 2.5-inch shift in the lava dome's location, is happening within the horseshoe-shaped crater that formed after the eruption.
Seismologists said there was no connection between activity at Mount St. Helens and a strong earthquake near Parkfield, California, or a smaller series of quakes in Alaska earlier this week.
The violent 1980 eruption of Mount St. Helens reduced its summit from 9,677 feet to 8,364 feet.
In addition to the 1986 eruption of the mountain's lava dome, strong earthquakes were detected in 1989, when fresh magma entered the volcano's lava system.
