A dormant volcano in Alaska rumbled back to life on Saturday, spewing ash, steam, and gas into the air. Cleveland Volcano is in a sparsely populated part of Alaska, but it lies below a major air-traffic route between the U.S. and Asia. Although aviation experts said the eruption was not major enough to be a threat to planes, some air traffic was diverted on Saturday. Cleveland Volcano first showed signs of life in the summer of 2011, when lava started oozing out and caused lava domes to form at the center—and pressure to build inside the volcano. There have already been 20 to 25 sporadic explosions since then, but experts said Saturday’s explosions were stronger, and long-duration airwave signals indicated a sustained eruption.