Alaska: Volcanic threat lower
2009-07-01 17:11
Anchorage - Seismic activity has slowed under Alaska's Mount Redoubt and it's possible that eruptions have stopped, the Alaska Volcano Observatory said. The observatory lowered its alert levels for the mountain 170 kilometers 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 measuring nearly 1 000 metres long, 450 metres wide and 200 metres tall, partly filling an old crater from a previous eruption that's about a 2km long and a 1km 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.
Ash plume 15km into the air
The volcano erupted March 22 and, in four blasts within about three hours, sent an ash plume more than 14.5 kilometres high into the air.
The last significant eruption occurred April 4, when Redoubt sent an ash plume 15km 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 December 15, 1989, sent ash 240km away into the path of a KLM jet carrying 231 passengers.
Its four engines flamed out and the jet dropped more than 3 000 metres before the crew was able to restart all engines and land the plane safely at Anchorage.
Dome 'may be unstable'
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.
- SAPA