"Cascade Range Summary"
Mount Hood, Oregon |
Mount Hood Volcano:
Snow-clad Mount Hood (3,426 meters - 11,239 feet) dominates the Cascade skyline from the Portland metropolitan area to the wheat fields of Wasco and Sherman Counties. The mountain contributes valuable water, scenic, and recreational resources that help sustain the agricultural and tourist segments of the economies of surrounding cities and counties. Mount Hood is also one of the major volcanoes of the Cascade Range, having erupted repeatedly for hundreds of thousands of years, most recently during two episodes in the past 1,500 years. The last episode ended shortly before the arrival of Lewis and Clark in 1805. When Mount Hood erupts again, it will severely affect areas on its flanks and far downstream in the major river valleys that head on the volcano. Volcanic ash may fall on areas up to several hundred kilometers downwind. Mount Hood was named after a British admiral, Lord Samuel Hood, and first described in 1792 by William Broughton, member of an expedition under command of Captain George Vancouver. -- Scott, et.al., 1997, and Swanson, 1989 The Past 30,000 Years: Eruptive activity at Mount Hood during the past 30,000 years has been dominated by growth and collapse of lava domes. The last two episodes of eruptive activity occurred 1,500 and 200 years ago. Repeated collapse of lava domes extruded near the site of Crater Rock, Mount Hood's youngest lava dome, generated pyroclastic flows and lahars and built much of the broad smooth fan on the south and southwest flank of the volcano. -- Scott, et.al., 1997 Quicksand River: In 1805, Meriwether Lewis and William Clark named a river on the south side of the Columbia River gorge the "Quicksand River." Their description of a wide, shallow river with a bed "formed entirely of quicksand," bears little resemblance to the narrow, moderately deep river we call today the Sandy River. What happened? The answer lay 50 miles away at Mount Hood. An eruption in the 1790's caused a tremendous amount of volcanic rock and sand to enter the Sandy River drainage. That sediment was still being flushed downstream when Lewis and Clark saw and named the river. Since 1806, the river has removed the excess sediment from its channel. The Toutle River in southwest Washington was similarly affected by the 1980 eruptions of Mount St. Helens. -- Gardner, et.al., 2000 Since 1820: No major eruptive events have occurred at Mount Hood since systematic records began in the 1820's. Reports of steam and tephra emissions accompanied by red glows or "flames" from the area of post-glacial vent are known from 1859, 1865 (twice) and 1903 A.D. No tephra deposits have been correlated with these events, though the summit area is capped by stratified tephra and scattered pumice blocks and breadcrust bombs. -- Swanson, 1989 MORE Mount Hood:
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