According to AVO, satellite infrasound detected the explosions starting at 5:00 AM Saturday. The organization noted that the sounds "suggest that this was a relatively short duration, low-level explosion."
The Cleveland Volcano is located on the remote Aleutian chain of islands, and is 940 miles from the city of Anchorage in Alaska, and about 45 miles from the community of Nikolski, according to Alaskan NPR affiliate KDLG.
The perfectly conical volcano is considered to be quite seismically active, and measures 1730 meters high, or 5,675 feet.
According to documents from the Smithsonian Institution, Cleveland last erupted in February 2001, producing ash clouds that rose a whopping 39,000 feet above sea level. Some minor ash emissions were also recorded in November 2012.
Volcanic ash is a big problem for aviation: the 2001 Cleveland eruption led to a number of potentially dangerous encounters with aircraft, according to an American Meterological Society paper on that event.
"Onboard radars can only occasionally detect concentrated ash within or near eruption plumes," noted the paper authors, explaining why aviation experts and researchers must keep a close eye on volcanic eruptions. "Only total avoidance of the ash ensures ﬂight safety."
The paper notes that per Smithsonian data, there are 158 volcanos that have been active in historical times in Alaska, and many flights pass by them.