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Ring of Fire

Posted: January 1, 2012 - 7:26am  |  Updated: January 9, 2014 - 2:38pm

The “Ring of Fire” sounds as if it should be part of a Tolkien epic, and in its own right, the tectonic plate boundary rimming the Pacific Ocean is every bit as fascinating, especially here on the Kenai Peninsula, which enjoys front row seating to one of the Ring’s most active zones.

Clearly visible within the north-south spine of the Chigmit Mountains across Cook Inlet from the peninsula are five active peaks — Spurr, Redoubt, Iliamna, Augustine and Douglas. They form the easternmost part of the Aleutian volcanic arc.

Except for an eruption on Redoubt recorded in early Spring 2009, the five magnificent mountains have been relatively quiet. 

Augustine, a 4,134-foot island mountain located west of Kachemak Bay burped steam and ash tens of thousands of feet in the air in 2006, but what looked to be the precursor to a larger eruption like the one that rained ash on Homer and Seldovia in 1986 instead petered out. The mountain does erupt on average about every 19 years and is overdue. Its behavior is unpredictable.

Cook Inlet sits atop a subduction zone where the Pacific Plate dives beneath the North American continent at roughly the speed of growing fingernails. The energy generated is tremendous and 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. The easternmost historically active volcano in the Aleutian arc, Spurr 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. Redoubt most recently erupted March 15, 2009, sending ash plumes from 30,000 to 60,000 feet high. The volcano remained active through early April, occasionally disrupting aircraft traffic. Before that, an eruption beginning Dec. 14, 1989, lasted into early 1990. Ash clouds reached heights of 12 miles, seriously disrupting air traffic as far away as Texas and threatening the Drift River Oil Terminal. The Volcano Observatory said total estimated economic costs associated with the eruption were $160 million, making that eruption the second most costly in U.S. history.

Mount Iliamna

10,016 feet, south of Redoubt, surrounded by glaciers radiating from its rambling multiple peaks. Iliamna has been quiet in recent times, though several “events” have been documented since 1741. Many are classified as “noneruptive” activity, others as “possibly not” eruptions.

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 generating a tsunami, a direct threat to Kachemak Bay communities. The island’s irregular coastline is testimony to repeated catastrophic collapse of the summit dome. According to studies cited on the Alaska Volcano Observatory Web site, at least 11 avalanches have occurred in the past two millennia, averaging one every 150 to 200 years.

Mount Douglas

7,020 feet, was active during the last Ice Age, but this, the southernmost inlet volcano, has been quiet during historic times. Atmospheric conditions often obscure Douglas behind a blue haze or clouds, but at certain times, especially mornings, it can be seen rising majestically above Cook Inlet.

 
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