A volcano on the Alaska Peninsula erupted with little advance warning over the weekend, spewing an ash cloud up to 6,000 metres high that prompted aviation warnings across the region.
Mount Pavlof, one of the most active volcanoes on the peninsula, began erupting shortly after 5 p.m. PT on Sunday, said Jessica Larsen, co-ordinating scientist with the University of Alaska Geophysical Institute.
"Pavlof is known to us for having a pretty quick onset to eruptions, it doesn't always give us long precursory signals," Larsen said.
"If you look at some of the seismic data that we have, the intensity really ramped up pretty fast. It was quite abrupt."
Photos on the Alaska Volcano Observatory website showed the plume towering over the icy slopes of Mount Pavlof and drifting to the northwest.
Red aviation alert
The Federal Aviation Administration issued a "red" aviation alert in response to the ash cloud, which required flights to be re-routed.
Alaska Airlines on Monday afternoon said it cancelled 41 flights affecting about 3,300 customers heading to Fairbanks, Bethel, Kotzebue, Nome, Barrow and Deadhorse.
The U.S. Geological Survey said in a news release late Monday night that the intensity of the eruption from Pavlof had "declined significantly."
The agency said the activity decline began around noon and that by late at night a continuous emission was no longer being observed by satellite.
Consequently, the volcano alert level was downgraded from warning to watch, though the agency says a significant eruption is still possible.
The closest residential area is Cold Bay, located 60 kilometres southwest of Pavlof.
There have been more than 40 eruptions from Pavlof, including a series between May and November of 2014, which also triggered aviation warnings because of ash. Such events can last weeks or months.
The highest recorded plume from the volcano was nearly 15,000 metres.