| Subject: volcanoes in Alaska |
Author:
Blobrana
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Date Posted: 14:02:06 01/31/05 Mon
Scientists are monitoring two volcanoes in Alaska that could erupt at any time.
Mount Spurr, 80 miles west of Anchorage across Cook Inlet, shook itself from a 12-year sleep in early July and has been in Code Yellow status ever since, with daily small earthquakes.
Code Yellow indicates an eruption is possible and could occur with no warning.
Mount Veniaminof, about 500 miles southwest of Anchorage on the Alaska Peninsula, changed from Code Green, or "dormant," to Code Yellow about Jan. 1. On Jan. 10, it was upgraded to Code Orange, indicating the volcano is "in eruption."
Ash plumes from Veniaminof can be seen on sunny days and have been photographed from planes. Even when clouds obscure the summit, seismic records indicate the eruption is continuing.
"We have some magma at Veniaminof.”
Reports have come from Perryville, 22 miles south-southeast of the volcano's summit, that its plumes have been flashing orange at night.
The volcano is experiencing what scientists call a "Strombolian eruption," a low-level, continuous eruption accompanied by minor ash plumes. The category is named after an Italian volcano that appears to have been erupting for about 2,500 years.
Both volcanoes are near to major airways. Volcanic ash, if blown high enough, poses a serious threat to aircraft.
The Veniaminof plume is apparently rising no higher than 12,000 feet, not enough to interfere with trans-Pacific air routes. The ash can pose risks to smaller planes at lower altitudes. Spurr is in its seventh month of elevated earthquake activity. The quakes however, are too small to feel.
About 15 per day occur about four miles below the mountain's summit. The mountain has not shown signs of an imminent eruption.
Since July, volcanologists have been analyzing data collected by instruments on and off the mountain, and they suspect that another group of small earthquakes has been occurring beneath Spurr's summit since 2003, but at the base of the Earth's crust, 12 to 25 miles down.
The two groups of earthquakes probably are linked to magma moving into cracks in the crust.
In mid-July and early August, observers flying above Spurr noticed small flows of mud and rock and a recently formed "ice cauldron" in the summit ice cap.
The collapse has been caused by increased heat from below the summit. The sink hole was about 165 feet in diameter and about half that in depth, and contained a pond of icy meltwater. It has since grown.
Mount Spurr erupted three times in 1992, spewing noxious ash over Anchorage and other cities.
Ash that fell on Anchorage in August 1992 was only a few millimetres thick. However, people were compelled to wear face masks, cover computers and change auto filters as they stirred up clouds of gritty ash wherever they walked and drove.
Before 1992, Spurr last blew its top in 1953. Both eruption sequences occurred below Crater Peak, a separate volcanic vent on Spurr, about 2.5 miles south of the summit.
The last time the summit vent is known to have erupted is about 5,000 years ago.
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