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Volcanoes make stirring sights

Posted: Monday, April 10, 2006

 

  Mount Augustine has been in an eruptive state since earlier this year. Photo courtesy Cyrus Read/Alaska

Mount Augustine has been in an eruptive state since earlier this year.

Photo courtesy Cyrus Read/Alaska

They’re majestic, imposing, even noble — and every so often, dangerous.

Few things trigger the imagination like a volcano, especially one that’s visibly active. Here on the Kenai Peninsula, we have ringside seats on the edge of to one of Earth’s most active geological regions, a tectonic plate boundary that’s part of the “Ring of Fire” rimming the Pacific Ocean.

And lately, it has been an active ring. Clearly visible within the north-south spine of the Chigmit Mountains across Cook Inlet from the peninsula are five active peaks, mounts Spurr, Redoubt, Iliamna, Augustine and Douglas. They form the easternmost part of the Aleutian volcanic arc.

Late last year, Augustine showed signs of activity after more than a decade of quietude. By January, the 4,134-foot mountain was periodically releasing clouds of steam accompanied by eruptions of ash that climbed tens of thousands of feet into the air. For safety’s sake, airline traffic was diverted around the region when this happened, or halted temporarily.

It looked then as if the volcano was gearing up for a major eruption, the kind that occurs, on average, every 19 years since around 1883. It was overdue. But by late February, the mountain looked to be settling down once again without any significant dusting of populated areas with a coating of pulverized stone as it had in 1986. But volcanic behavior is unpredictable, and one never knows.

Cook Inlet sits atop a subduction zone where the Pacific Plate dives beneath the North American continent at roughly the speed of growing fingernails. Despite that leisurely pace, the energy generated is tremendous and is responsible for pushing up the area’s mountain ranges, shaking the surface with frequent and sometimes devastating earthquakes and heating mantle material that occasionally finds its way to the surface in spectacular fashion.

The Alaska Volcano Observatory in Anchorage monitors the area’s volcanic peaks constantly. Information on current activity can be found at the observatory’s Web site at www.avo.alaska.edu. Volcanoes visible from the Kenai Peninsula, from north to south, are:

· Mount Spurr, 11,070 feet, nearly due west of Anchorage. Erupted in 1953 and 1992, dumping ash on the city and closing the airport.

· Mount Redoubt, 10,197 feet, dominates the western horizon from the central peninsula. An eruption beginning Dec. 14, 1989 lasted into early 1990. Ash clouds reached heights of 12 miles, shutting down air traffic and threatened the Drift River Oil Terminal. It also erupted in 1966 and 1968.

· Mount Iliamna, 10,016 feet, south of Redoubt, surrounded by glaciers radiating from its rambling multiple peaks. Iliamna has been quiet in historic times.

Mount Augustine, 4,134 feet, occupies its own island in Kamishak Bay about 70 miles due west of the mouth of Kachemak Bay. Erupted in 1883, 1908, 1935, 1963-64, 1976, 1986 and 2005-06. Of all the Cook Inlet volcanic peaks, Augustine poses the greatest threat of tsunami. Concern surrounds the possibility that during an eruption, its slope could slide into the sea, generating a tsunami aimed at Kachemak Bay.

· Mount Douglas, 7,020 feet, southernmost inlet volcano. It has not erupted in historic times, but was active during the last Ice Age.



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