After more than two dozen explosions, Bogoslof Volcano has finally dropped ash on Unalaska.
In its longest eruption since activity began six weeks ago, the volcano dusted the island with less than a millimeter of ash Monday night and produced a strong sulfurous smell.
The eruption lasted eight hours, starting at 8:20 p.m. with a series of explosions that eventually morphed into a continuous ash plume.
Kristi Wallace -- a geologist with the Alaska Volcano Observatory (AVO) -- said the eruption signals a change in behavior for Bogoslof, which has typically produced short, standalone bursts.
“Monday night’s activity was very interesting," said Wallace. "There were many pulses. It lasted for many hours. So there certainly was some kind of a shift last night, and hopefully we can understand that in the coming hours.”
Meanwhile, the eruption has subsided, and the 25,000-foot ash cloud is dissipating as it moves east.
Wallace said the small amount of ash is not a health risk for Unalaska residents.
“No real concerns right now," she said. "It’s probably not more than driving down a dusty road on a dry day.”
Scientists don’t worry about air quality until several millimeters of ash have accumulated, and it’s been quite a while since Bogoslof produced that much.
“The last report of that amount of ash was in 1906," said Wallace. "I think there was six millimeters of ash. So that would be considered significant, and we would be monitoring the situation closely at that point.”
Still, the AVO is keeping a careful eye on Bogoslof right now, especially as the volcano’s new behavior has made it harder to predict potential emissions. Scientists have raised its alert level to “warning,” citing its “heightened state of unrest and unpredictable condition.”
PenAir canceled Unalaska’s midday flight because of the volcano.