Mount Redoubt, an active volcano 100 miles (180kms) southwest of Anchorage, Alaska is rumbling and simmering, with geologists warning an eruption is imminent.

Mount Redoubt has previously erupted in 1902, 1966 and 1989. The eruption in 1989 spewed volcanic ash 45,000 ft (14,000 m) into the air, throwing ash over an area of about 7,700 sq. miles (20,000 km²) including the Anchorage area.

Authorities are warning Alaska residents to prepare a disaster plan, stock up on food and limit outdoor activity.

Volcanic ash features small, jagged pieces of rock and glass that can cause damage by direct exposure.