There is no real-time seismic monitoring network on Cleveland Volcano, meaning scientists must rely on limited data, such as pilot reports, webcam images and low-frequency sounds. A pilot report suggests the ash cloud rose to an altitude of 35,000 feet, or 6.6 miles. The sounds detected suggest it was a brief eruption.
The Alaska Volcano Observatory says additional eruptions are still possible with little warning, and ash clouds 20,000 feet above sea level are possible.
The 5,675-foot volcano is on an uninhabited island about 940 miles southwest of Anchorage.
Seismologist Stephanie Prejean says the explosion, at this point, appears to be within the range of those reported from the volcano during the past year.