Check out these Mount Redoubt photos from previous years.
Mount Redoubt web cams are available through the Alaska Volcano Observatory.
More Alaska volcano video:
ANCHORAGE, Alaska -- Mount Redoubt, a volcano 100 miles southwest of Anchorage, is rumbling and simmering, prompting geologists to warn that an eruption may be imminent.
Scientists from the Alaska Volcano Observatory have been monitoring activity round-the-clock since the weekend.
On Thursday, the observatory said: "Seismicity remains above background and largely unchanged with several volcanic earthquakes occurring every hour."
The last time the 10,197-foot peak blew was during a five-month stretch starting in December 1989. It disrupted international air traffic and placed a layer of volcanic dust throughout the Anchorage area.
Volcanoes in Alaska, including Redoubt, typically erupt explosively, shooting ash almost eight miles high. Volcanic ash features small, jagged pieces of rock and glass.
This differs from volcanoes in Hawaii, which usually have slow rolling lava ooze out.
The difference is gas trying to escape gets blocked, possibly by a lava dome or a viscous magma that increases the power from beneath, said observatory geologist Jennifer Adleman.
"Its pressure keeps building and building," she said.
Depending on wind, the ash plume could be pushed straight at Anchorage, the state's largest city. This has prompted state and city officials to post bulletins on how to deal with the ash. Tips include staying inside, wearing a mask or wet bandanna if going outside and wearing goggles over contact lenses.