Scientists have downgraded the alert level at one of Alaska's most active volcanoes after a sustained pause in volcanic unrest.
This comes after the Alaska Volcano Observatory raised Cleveland Volcano's alert level to "advisory" early in the summer, after a short-lived explosion on the evening of June 1.
According to Aaron Wech, a seismologist with the AVO, Cleveland Volcano usually stays at an elevated color code and alert level. But scientists lowered both the aviation color code and alert level to "unassigned" on Wednesday, since the volcano — which is located on an uninhabited island in the central Aleutians, west of Umnak Island — had gone three months without signs of activity.
"Pretty much nothing has happened since that explosion in early June," Wech said. "So it's been a really long pause. We've seen no signs of any surficial activity from satellite data or signs of seismicity. It's just been really quiet."
How the AVO approaches the classifications of color code and alert level is complicated. Wech said scientists generally like to have three or more instruments on a volcano to monitor its activity. But Cleveland only has two seismometers on it, which, he said, isn't sufficient to pinpoint the exact location of something like an earthquake, which can cause volcanic unrest.
So, when activity decreases at Cleveland, like it has recently, rather than lowering the alert level from "advisory" to "normal," and the color code from "yellow" to "green," like they would at a more monitored volcano, scientists have to classify it as just "unassigned" in color and code.
"The color code, from our perspective, and how we monitor it, doesn't really change what we're doing," Wech said. "It's just what the public needs to know about the level of activity at the volcano."
When Cleveland erupted in early June, it had gone nearly a year and a half without an eruption, which is the longest time Cleveland has gone without one since 2005. And it seems that similarly now, the volcano is having a quiet period.
According to Wech, this lack of activity is not unusual at the unpredictable volcano. He said Cleveland has a long history of cycles of explosions and inactivity.
Despite the current pause, the eruptive period at Cleveland — dating back to 2001 — remains ongoing and future explosions are likely, he said. These occur without warning and typically generate small clouds of volcanic ash that are a hazard in the immediate vicinity of the volcano. Though, Wech said, more significant ash emissions are possible.
"This volcano is very tricky because it doesn't have a lot of precursory activity," he said. "So it tends to go from just really quiet to exploding. And sometimes we will see some things in satellite data, we can see signs of the summit crater becoming a little bit warmer, which may mean there's some magma intruding up higher into the conduit, but we can definitely have months of pauses or breaks between explosions."
Wech said the AVO will continue to monitor the volcano closely.