Observatory volcanologist Robert McGimsey says Wednesday afternoon's eruption of the Bogoslof volcano was "almost a carbon copy" of an eruption 24 hours earlier.
He tells The Associated Press that both eruptions prompted the highest alert level and both were downgraded hours after the events.
Tuesday's eruption sent ash and steam 34,000 feet into the air, while Wednesday burst went 1,000 feet higher. Officials say both volcanic explosions were also short-lived.
The observatory said early Thursday that it was reducing the alert level because there had been no recent volcano activity.