Bogoslof volcano, in Alaska's Aleutian Islands, erupted yet again Friday night.
The eruption started at 10:30 p.m. and lasted about 45 minutes, the Alaska Volcano Observatory said in an online report. "Low-level eruptive activity" started again at 5 a.m. Saturday, AVO said, and is ongoing.
"This activity is weaker than prior explosions, including (Friday) night's, but is relatively continuous, indicating persistent unrest," the report said.
An aviation alert from AVO remained at red, its highest level. A "warning" alert also continued, meaning an eruption is imminent or underway.
Peter Cervelli, a geophysicist with the U.S. Geological Survey who also works with AVO, said an ash cloud from the eruption potentially reached as high as 30,000 feet. A plume was not observed in satellite data at the time of the eruption, Cervelli said, because "the region was covered in high clouds."
"Fifteen years from now, we will refer to this whole thing as the Bogoslof eruption of 2016," Cervelli said of the ongoing activity since earlier in December.
It's "not unusual" for eruptive sequences to last weeks or even months, Cervelli said.
It's difficult for scientists to monitor activity at Bogoslof because of how small the island is. No ground-based instrumentation is situated there, Cervelli said. If any seismometers or GPS devices had been at Bogoslof, "they'd all be gone by now." That means scientists have to use detection devices from farther away.