Alaskans can put away their dust masks and spare air filters, for now, because Mount Redoubt seems to have cooled off since its last major eruption nearly three months ago.
The Alaska Volcano Observatory said Tuesday that seismic activity has slowed under the volcano and it's possible that eruptions have stopped. The observatory lowered its alert levels for the mountain 106 miles southwest of Anchorage.
A series of eruptions beginning in March disrupted air traffic and dusted Anchorage, the Kenai Peninsula and Gov. Sarah Palin's hometown of Wasilla with volcanic ash. Based on past events, geologists said eruptions could last for months, but Redoubt's last significant blast was April 4.
Over the last three months, volcanic activity continued with the growth of a lava dome with enough material to fill 16 Louisiana Superdomes, geologist Ryan Bierma said. The bubble measures nearly 3,300 feet long, 1,500 feet wide and 656 feet tall, partly filling an old crater from a previous eruption that's about a mile long and a half mile wide.
The dome grew from lava flowing out of the mountain and magma pushing up from below, Bierma said, but growth has slowed significantly.
"There hasn't been much change noted since early June," he said.
The volcano erupted March 22 and, in four blasts within about three hours, sent an ash plume more than 9 miles high into the air. The last significant eruption occurred April 4, when Redoubt sent an ash plume 50,000 feet into the air.
The eruption sent southcentral Alaska residents scrambling for masks and air filters to protect their lungs. Jagged ash particles have been used as an industrial abrasive. Particulate can injure skin, eyes and breathing passages and can scratch windshield glass if a motorist turns on wipers.
It can also harm engines. Volcanic ash from Redoubt on Dec. 15, 1989, sent ash 150 miles away into the path of a KLM jet carrying 231 passengers. Its four engines flamed out and the jet dropped more than 2 miles before the crew was able to restart all engines and land the plane safely at Anchorage.
Geologists monitored the mountain and watched as seismic activity diminished. In flights over the dome, they also detected less gas emitted.
They used forward looking infrared cameras pointed at the dome to detect where cracks were occurring and where magma was close to the surface, Bierma said. The eruptions melted much of a glacier that had covered the crater, but parts of the dome are now so cool, new snow has not melted.
Scientists say the dome may be unstable and could fail with little or no warning, leading to significant ash production and possible mud flows in the Drift River Valley, where an oil terminal was threatened in April.