A lava dome is growing at Cleveland Volcano as its current slow eruption continues, a sign that the restless Aleutian volcano could pop at any moment, the Alaska Volcano Observatory says.
Satellite images show the lava dome has expanded from about 50 meters to 60 meters across in the past week. The hardening lava still only occupies a small part of the roughly 200-meter crater, the observatory says.
The 5,676-foot volcano makes up the western half of Chuginadak Island about 940 miles southwest of Anchorage. If Cleveland's eruption turns explosive -- perhaps blasting ash up thousands of feet, into trans-Pacific flight paths -- it could disable the engines of airplanes that fly through it.
The explosiveness is characteristic of Alaska volcanos, scientists say.
Lava extruding inside Cleveland Volcano is thick and pasty, "like peanut butter," volcanologist Steve McNutt said.
"The lava's so viscous, it doesn't flow like you're used to seeing in pictures of Hawaii, where it's fluid and runny," McNutt said. "So it piles up and makes a round, dome-like lava flow."
The molten rock flows out of vents inside the volcano's crater and piles up, McNutt said. When the dome grows so big that it covers those vents, gas builds up behind it, he said.
Then, when the pressure is high enough: ka-boom.
A similar explosive event in December mostly cleared a lava dome that had been growing since October, according to the observatory. The brief explosion sent ash up to about 15,000 feet.
The difficulty of monitoring Cleveland Volcano comes from its remoteness. Unlike many other Alaska volcanos, Cleveland has no seismometers on its flanks, so scientists cannot hear its inner rumblings. Instead, they rely on seismometers farther away, satellites that can sometimes be blocked by clouds, and lightning detectors that sense lightning in volcanic ash plumes already high in the air.
Plans are in the works to maybe put sensors on Cleveland Volcano but "that's just in the talking stage now," McNutt said.
Until then, the volcano could disrupt air travel with little warning.
"There's a half-dozen major flight paths that go from Asia to North America and Europe that fly over Alaska airspace," he said. "So it does depend on which way the wind is blowing but there's a number of paths that are near it."