The Petersburg police chief says a man who was injured in an explosion detonated an explosive mixture in a gravel or rock pit owned by the borough.

Chief Kelly Swihart tells the Juneau Empire there is no evidence that the 59-year-old man was trying to injure others since there's no homes or buildings nearby.

But Swihart says they don't know what he was doing there Sunday.

The injured man was taken to a Seattle hospital, where he was reportedly in serious condition Tuesday. Police have not released the man's name.

About 20 pounds of a commercially-available explosive material in a 5-gallon bucket was found in his vehicle. Authorities also found two other buckets of the material during searches at another location.

The explosives will be detonated.