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| 09/14/01 By RICHARD L. HILL of the Oregonian, used with permission Small earthquakes have been rumbling under Mount Hood this week, but scientists say it's just business as usual for the volcano. Instruments around the 11,240-foot mountain have detected more than a dozen earthquakes since Sunday, all too small to be felt. The sensors indicate the quake swarm has been about five miles south of the summit beneath the Government Camp area at depths ranging from 11/2 to 3 miles. Seismometers recorded a magnitude 2.0 earthquake at 5:11 a.m. Thursday. The largest of the quakes, a magnitude 2.4, occurred at 2:26 p.m. Wednesday. Occasional flurries of earthquakes are common at Mount Hood and do not indicate an impending eruption, said Cynthia Gardner, a geologist with the Cascades Volcano Observatory in Vancouver, Wash. "We view them as part of the natural process that is happening," Gardner said. "We're keeping an eye on them." The exact cause of the earthquakes is unknown. Scientists say the tremors are caused by changes in the volcano's magma plumbing system or by a complex system of faults. About 20 earthquake swarms have been detected at the mountain in the past decade. More than three-quarters of the roughly 400 quakes at Mount Hood since 1990 have occurred in such swarms. Most flurries occur southeast of the summit a couple of miles from this week's events. Those quakes occur beneath the vicinity of the Mount Hood Meadows ski area. Last month, instruments detected about 15 small quakes, the largest a magnitude 1.3, in that area. The largest recorded earthquake at Mount Hood was a magnitude 4.0 in 1974. The last eruption occurred about 200 years ago. You can reach Richard L. Hill at richardhill@news.oregonian.com or 503-221-8238. |
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