A volcano just 100 miles from Alaska's largest city has stirred back to life after nearly 20 years of tranquility, sparking a round-the-clock eruption watch, seismologists said Thursday.
The fresh wave of seismic activity at Mount Redoubt suggests that the eruption could occur within days or weeks, the Alaska Volcano Observatory reported.
Redoubt's renewed tremors sparked worries about potential ashfall in Anchorage, where city officials advised residents to stock up on supplies ranging from extra food and water to respirators, plastic bags and windshield washer fluid.
Volcanic ash and mudflows spewed from Redoubt during its last eruptive episode — a five-month stretch that began in December 1989. Those eruptions created health hazards and cleanup headaches for surrounding communities. The mudflows caused partial flooding at an oil terminal facility, and the ash plumes disrupted international air traffic.
The long hiatus at the 10,197-foot peak came to an end last fall, when seismic instruments registered an increase in activity. On Jan. 23, the levels increased markedly, leading the observatory to raise the alert level for aircraft and emergency officials.
On Thursday, the observatory reported that the activity was "largely unchanged with several volcanic earthquakes occurring every hour."
The observatory's seismologists said the most probable outcome would be an eruption "similar to or smaller than the one that occurred in 1989-90 ... within days or weeks." A more explosive eruption could send threatening mudflows or landslides down the Drift River and other drainages, but that scenario was "much less likely," the observatory said.
Observatory staff members are checking instrument readings and satellite images around the clock to watch for temperature changes, said volcanologist Dave Schneider. A Webcam was installed about 7.5 miles from the summit, and additional seismic equipment will be installed at the volcano as weather permits.
Observers will also look to weather radar scanners near the Kenai airport for help. Those scanners send data in six-minute intervals. These scanners will be able to detect an ash plume should one appear, Schneider said.
This report includes information from The Associated Press and msnbc.com.