Seismic tremors and rattling earthquakes shook Mount Redoubt for about 20 minutes Thursday afternoon but didn't produce an eruption, according to the Alaska Volcano Observatory.
Commencing at 3:07 p.m., the shaking was both stronger and longer than a four-minute-long episode that hit that morning -- which geologists characterized as "the most energetic" seismic activity at Redoubt in a week.
"There was probably a lot of gas venting" during the second episode, said observatory geologist Chris Waythomas.
While Web cameras and satellite images were obscured by clouds throughout the day, radar and pilot observations confirmed that no eruption had occurred, he said.
The radar images, recorded at the Kenai Airport, can "see through" clouds or the dark of night and discern an ash plume any time of day. The images are updated every five minutes.
If snow is falling, as it was near Redoubt on Thursday, the ash would be obscured on the radar until it rose above cloud level at about the 15,000- to 20,000-foot level, Waythomas said. The last time Redoubt erupted, beginning on Dec. 14, 1989, the mountain shot ash more than 40,000 feet high.
Located about 100 miles southwest of Anchorage, Mount Redoubt has been closely monitored by Alaska volcanologists ever since seismic activity increased significantly there on Jan. 25.
Since then, the observatory has classified its own alert level for the 10,197-foot peak as "watch" and its aviation color code warning as "orange."
Find George Bryson online at adn.com/contact/gbryson or call 257-4318.