Report on Hood (United States) — July 2002
Bulletin of the Global Volcanism Network, vol. 27, no. 7 (July 2002)
Managing Editor: Richard Wunderman.
Hood (United States) Strongest earthquake in decades registered on 29 June 2002 (M 4.5); aftershocks
Please cite this report as:
Global Volcanism Program, 2002. Report on Hood (United States) (Wunderman, R., ed.). Bulletin of the Global Volcanism Network, 27:7. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN200207-322010.
45.374°N, 121.695°W; summit elev. 3426 m
All times are local (unless otherwise noted)
The strongest earthquake in the Mount Hood area in decades occurred on 29 June 2002 at 0736, according to the USGS Cascades Volcano Observatory (CVO). The widely felt M 4.5 event was located ~4.5 km S of the summit (figure 3) at a depth of 6 km. Hundreds of aftershocks followed, including two greater than M 3. Typically, several earthquake swarms occur each year at Mount Hood.
|Figure 3. A map of all earthquakes (M 1.0) that occurred at Hood from the start of 2001 to 29 June 2002. The area shown details a few kilometers around the M 4.5 event on 29 June 2002. Courtesy PNSN.|
Geologic Background. Mount Hood, Oregon's highest peak, forms a prominent backdrop to the state's largest city, Portland. The eroded summit area consists of several andesitic or dacitic lava domes. Major Pleistocene edifice collapse produced a debris avalanche and lahar that traveled north down the Hood River valley and crossed the Columbia River. The glacially eroded volcano has had at least three major eruptive periods during the past 15,000 years. The last two occurred within the past 1800 years from the central vent high on the SW flank and produced deposits that were distributed primarily to the south and west along the Sandy and Zigzag rivers. The last major eruptive period took place beginning in 1781, when growth of the Crater Rock lava dome was accompanied by pyroclastic flows and lahars down the White and Sandy rivers. The Sandy River lahar deposits extended to the west as far as the Columbia River and were observed by members of the 1804-1805 Lewis and Clark expedition shortly after their emplacement. Minor 19th-century eruptions were witnessed from Portland.
Information Contacts: Cascades Volcano Observatory (CVO), United States Geological Survey (USGS), 5400 MacArthur Blvd., Vancouver, WA 98661, USA (URL: https://volcanoes.usgs.gov/observatories/cvo/); Pacific Northwest Seismograph Network (PNSN), University of Washington, Department of Earth and Space Sciences, Box 351310, Seattle, WA 98195-1310, USA (URL: http://www.ess.washington.edu/SEIS/PNSN/).