Pop top in Alaska

• R. Clucas/Alaska Volcano Observatory
• U.S. Geological Survey
• U.S. Geological Survey
• U.S. Geological Survey
• U.S. Geological Survey
• U.S. Geological Survey

• Sept. 6, 2004: Redoubt Volcano looms behind a fish processing plant on the Kenai River, in Kenai, Alaska. The volcano, about 100 miles southwest of Anchorage, is rumbling and simmering, prompting geologists to warn that an eruption may be imminent.
• June 1, 1990: A structure near the mouth of Drift River 22 miles from the Redoubt Volcano is buried in frozen mud streams from the 1989 to 1990 eruptions of the volcano.
• 2005: Two fishermen pick red salmon from their nets in Cook Inlet off Clam Gulch, Alaska, with the Redoubt Volcano in the background. The volcano, about 100 miles soutwest of Anchorage, is now rumbling and simmering, prompting geologists to warn that an eruption may be imminent.
• Jan. 29 2009: Elizabeth Ketting looks at dust masks at the Alaska Industrial Hardware store in Anchorage, Alaska as she and others make preparation in case the Mount Redoubt volcano erupts. The volcano 100 miles southwest of Anchorage, is rumbling and simmering, prompting geologists to warn that an eruption may be imminent.
• Jan. 27, 2009: Rolling fog on Cook Inlet at Kenai, Alaska, partially obscures the 10,197-foot Mount Redoubt volcano at sunset. Scientists at the Alaska Volcano Observatory say that an eruption is possible.
• April 5, 1990: A lava dome � the last of a series of 14 lava domes that erupted in 1989 to 1990 � is precariously perched high on Redoubt Volcano's steep north flank. Each of the previous domes were destroyed as they collapsed down the north flank and across a glacier. The hot lava rocks carried by the pyroclastic flows melted snow and ice quickly and generated frozen mud flows that swept down Drift River valley. This dome (dark mound in center) began erupting four days earlier on April 21, and is about 328 ft. in diameter.
• March 10, 1990: Dark pathways of a frozen mud flow streak the snow-covered Drift River valley after a lava dome collapsed down the steep north flank of Redoubt Volcano. This relatively small mud flow swept 22 miles down Drift River valley to Cook Inlet. A few of the flows were large enough to inundate the entire valley floor, which is about 1.2 miles wide in this photograph.
• March 10, 1990: Dark pathways of frozen mud flows move past an oil terminal marked by the white rectangle in the lower center of the photograph. As the flow moved down Drift River, it became diluted with additional snow melt and passed on both sides of the facility. Flows triggered by the growth and subsequent collapse of Redoubt's many lava domes generated concern about the safety of the oil tanks and people working at the site.
• April 23, 1990: In hopes of detecting and tracking frozen mud flows as they moved down the Drift River scientists installed 3 seismometers sensitive to ground vibration at relatively high frequencies along the edge of the valley. The sensors are called acoustic-flow monitors (AFM) to distinguish them from traditional seismometers. The AFM's were installed at increasing distances from the volcano � the nearest station at the base of the volcano was installed about 5.5 miles from the dome.
• April 21, 1990: "Ascending eruption cloud from Redoubt Volcano as viewed to the west from the Kenai Peninsula. The mushroom-shaped plume rose from avalanches of hot debris (pyroclastic flows) that cascaded down the north flank of the volcano. A smaller, white steam plume rises from the summit crater."