After a year of restlessness, Alaska’s Mount Cleveland volcano sent an ash cloud to an altitude of 35,000 feet (10 km) on Tuesday, prompting the Alaska Volcano Observatory (AVO) to raise the aviation alert from yellow to orange — the third highest of four levels.
Located 940 miles (1,500 km) southwest of Anchorage on a remote, uninhabited island in the Aleutian Chain, Cleveland’s primary threat is not on the ground but above, in Alaska’s heavily travelled air corridors.
Most air freight between Asia and North America, and between Asia and Europe, flies through Alaskan airspace, as do about 20,000 passengers per day. Volcanic ash not only reduces visibility but can disrupt navigational instruments, and along with volcanic gases, can cause loss of thrust in jet engines.
Lacking a real-time seismic monitoring network on the 5,676-foot (1,730 m) volcano, AVO relies on satellites — as well as seismic, infrasound, and volcanic lightning networks — to monitor activity. Frequently, eruptions are first observed by pilots; in fact, the altitude of Tuesday’s ash cloud was estimated based on a pilot’s report.
Mount Cleveland has erupted at least 22 times in the last 230 years, making it one of the most active of more than 75 active volcanoes in the Aleutian Arc.
The volcano’s most recent, significant eruption occurred in 2001, when 3 explosive events produced ash clouds reaching as high as 39,000 feet (12 km) above sea level. More recent but smaller events include three eruptions in 2009, two in 2010, and one in 2011.
Although no significant activity has been reported since Tuesday, the latest update from AVO advises that “Additional sudden explosions of blocks and ash are still possible with little warning. It is possible for associated ash clouds to exceed 20,000 feet above sea level.”