One of Alaska's most active volcanos has calmed down since spewing ash up to 35,000 feet into the air over the weekend, but scientists said Monday the volcano has a pattern of prolonged eruptions of varying intensity. They're not ready to consider this explosion over.
Pavlof Volcano began erupting Wednesday, culminating with a major blast Saturday that lasted seven or eight hours before its seismic activity dramatically dropped.
The National Weather Service warned aircraft to avoid the area over the weekend because of the ash plume.
Here are some other facts about Pavlof:
RING OF FIRE
Pavlof is in a volcano-rich, sparsely populated region about 625 miles southwest of Anchorage on the Alaska Peninsula.
The Alaska Volcano Observatory says the volcano has erupted more than 40 times in recorded history, including earlier this year and last year.
It is Alaska's second most active volcano. The first is Shishaldin, which has had about 55 eruptions, including a low-level one that's been ongoing for several months, said Michelle Coombs, a U.S. Geological Survey geologist at the Alaska Volcano Observatory.
Pavlof is among 52 historically active volcanos in the Aleutian arc of the "Ring of Fire" string of volcanos encircling the Pacific Ocean, Coombs said.
Pavlof eruptions typically involve gas-rich fountains of lava that can shoot up to a few thousand feet. Its ash clouds usually are lower and less dense than the plumes of more explosive volcanos that pose a greater hazard to aircraft, according to scientists.
But it could still spew out much higher plumes, as demonstrated by Saturday's explosion.
"That was a very unusual eruption for Pavlov," Coombs said. "It was much more energetic than we've seen the last 10 years or so."
DANGER IN THE AIR
The volcano lies along popular international air routes connecting Europe, North America and Asia.
International jets generally fly at altitudes between 30,000 and 45,000 feet, but airlines are notified about ash plumes at all levels. It's up to individual carriers to decide whether to avoid areas with lower plumes, according to Nathan Eckstein, the weather service volcanic ash advisory center manager in Anchorage.
Regional airlines with smaller planes flying at lower altitudes are used to flight disruptions because of Alaska's volcanoes. There's no average for how many times the larger airlines are affected, though it can range from a couple to 100 days a year, according to Eckstein.
HAZARDS FOR PEOPLE
Any kind of lava flow from Pavlof could cause mudflows, but they likely would be minor and limited to uninhabited areas.
Winds can push ash to the nearest communities, including Cold Bay and Sand Point, but Saturday's plume drifted away from inhabited areas.
Ash fall can cause scratchy throats and watery eyes, even though no more than traces have been reported from previous Pavlof eruptions.
HOW LONG WILL THE ACTIVITY LAST?
Pavlof's eruptions may continue for weeks or months with varying levels of intensity. The apparent pause in the eruption is part of its character.
"It tends to go through these dramatic ups and downs during an eruptive phase," Coombs said. "It could jump up again and begin to erupt with very little notice."
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