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It’s code orange for Mount Redoubt, the Alaskan volcano whose rumblings have had geologists predicting an eruption since January.
Officials at the Alaska Volcano Observatory raised the threat level yesterday from yellow, which indicates elevated unrest, to orange, the stage just before eruption when its unrest is escalating or a volcano is emitting minor amounts of ash. Red is the highest level, when eruption is imminent or underway. Geologists had just lowered the threat level to yellow last Tuesday when they began to detect movement of magma within Redoubt’s cracks and fractures, which produces a specific signal, the Associated Press reports.
"We got a return of this stuff we call volcanic tremors," geologist Chris Waythomas told the AP. “We think it's associated with the hydrothermal system there. It's being reinvigorated."
Steam and ash from the volcano rose 15,000 feet above sea level yesterday, the AP noted. Volcanoes in Alaska typically shoot ash upward (20 years ago, a plume from Redoubt knocked out a jet’s engines); tests will show whether the ash contains new magma or remnants of old rumblings.
Redoubt is 103 miles (166 kilometers) southwest of Anchorage and is 10,200-feet (3,100 meters) tall. We’ve got more on why volcano monitoring is important and what causes a volcano to erupt.
Updated at 5:50 p.m. March 16 to correct height of Mount Redoubt.
Ash and steam plume from Mount Redoubt, March 15, 2009 by Heather Bleick, AVO/USGS