Photo by Michael Armstrong Mount Redoubt steams at sunset on Tuesday, March 31.

Overflights this week confirmed a lava dome has been growing on Redoubt's summit, with occasional avalanches of hot blocks tumbling down the north flank. Thermal sensors have measured temperatures of about 900 degrees Fahrenheit at the dome. Seismographs near Redoubt have shown a tell-tale "drumbeat" pattern of three-to-four small earthquakes a minute indicative of lava extrusion and dome growth, U.S. Geological Survey geologist Chris Waythomas said at a press conference on Thursday.

That dome growth is inherently unstable. Lava domes have steep flanks, Waythomas said. The dome also could fail if pressure builds up in the dome. A sudden collapse or explosion can occur without warning and produce large ash clouds 25,000 feet, as was seen in a dramatic explosion on April 21, 1990.

Trace amounts of ash less than 1/32-inch were reported this week in Kenai and Valdez. A volcanic haze also has been seen over southcentral Alaska.

For updates, visit www.avo.alaska.edu or phone the AVO 24-hour recording at (907) 786-7478.

Michael Armstrong can be reached at michael.armstrong@homernews.com.