An Alaska volcano spewed an ash cloud with an estimated of height of 23,000 feet, according to CNN. Although Cleveland Volcano, which forms the western half of Chuginadak Island off the coast of mainland Alaska, hasn’t coughed up anything else since Tuesday, officials are keeping aerial alert levels at “orange/watch” until they’re certain another eruption isn’t in the cards. Orange is considered to be the second most serious of the levels.

Alaska Volcano Observatory posted the following information on their website:

Additional sudden explosions of blocks and ash are possible with little or no warning. It is possible for associated ash clouds to exceed 20,000 feet above sea level. If a large ash-producing event occurs, seismic, infrasound, or volcanic lightning networks should detect the event and alert AVO staff. There is no real-time seismic monitoring network on Mount Cleveland so AVO is unable to track activity in real time.

According to the observatory, Cleveland Volcano experienced a significant eruption in 2001, causing clouds to rise as high as 7.5 miles above sea level.

Ash clouds, as many pilots will tell you, can easily disrupt air travel. Last year, for example, Grimsvotn Volcano in Iceland spit forth plumes that were seven miles high. In addition to causing numerous flight cancellations and stranding countless travelers at airports, the volcano is also responsible for several earthquakes in the region at the time.