Wednesday, July 23, 2008

Volcanoes Erupting in Alaska

Here's some news from the old country. Okmok Volcano on Umnak Island in the eastern Aleutian Islands (the end near the mainland) started erupting on July 12 and continues to produce explosions and ash plumes through a newly created vent. The initial eruption sent a cloud to 35,000 feet. Most of ash and gas from that explosion blew southward over the North Pacific, but some of it spread eastward enough to reach the port of Dutch Harbor. Sulfur dioxide injected into the upper atmosphere stayed aloft long enough to drift south and get caught in the mid-latitude wins that blow eastward across the lower forty eight United States. It was detected as far inland as Eastern Montana on the 17th. Mount Cleveland on Chuginadak Island and ninety miles west of Okmok burst into action on Monday with a 20,000 foot plume. Two eruptions at once is a rare event and will keep the state geologists busy for the next few weeks.

Alaska has more big, active volcanoes than the the rest of the United States combined. They can affect the global climate and crops, but you hear much less about them because most of them only directly endanger a small number of people. That is a function of how large and sparsely populated Alaska is. Umnak Island, for example is larger than Oahu in Hawaii. But while Oahu has almost nine hundred thousand people, Umnak has only thirty nine--not thirty nine thousand, just thirty nine people. Although these volcanoes are on the end of the Aleutians closest to the mainland, they are still almost a thousand miles away from Anchorage. The tourists on the cruise ships sailing into Southeastern Alaska and Anchorage will not be aware that two volcanoes are erupting in the state unless they buy a local newspaper.

Okmok is a shadow of its former self. The current erupting cone sits inside the crater rim of a collapsed caldera almost exactly the same size as Crater Lake in Oregon. Okmok has apparently undergone two caldera collapses in the last 10,000 years. The earlier was around 6200 BC, or five hundred years before Mazama became Crater Lake. The more recent collapse was in about 400 BC. Both of those occurred while people were living in the Aleutians, possibly on that island.

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