|
The most serious tephra hazards in the region are due to Mount St. Helens, the most prolific producer of tephra in the Cascades during the past few thousand years. This map provides estimates of the annual probability of tephra fall affecting the region, based on the combined likelihood of tephra-producing eruptions occurring at Cascade volcanoes, the relationship between thickness of a tephra-fall deposit and distance from its source vent, and regional wind patterns. Probability zones extend farther east of the range because winds blow from westerly directions most of the time. The map shows probabilities for a fall of 10 centimeters (about 4 inches) or greater. Northern Skamania County has an annual probability of a tephra fall of 10 centimeters or more of about 1 in 100 (1%) to 1 in 500 (0.2%). Even though Mount Adams is a meager tephra producer, the region around Mount Adams has the highest probability of tephra fall of anywhere in the western conterminous United States, owing to its location just downwind of Mount St. Helens.
-- Excerpt from: W.E. Scott, R.M. Iverson, J.W. Vallance, and W. Hildreth, 1995, Volcano Hazards in the Mount Adams Region, Washington: U.S. Geological Survey Open-File Report 95-492 
|
Return to:
[Cascade Range Volcanoes and Volcanics Menu] ...
[Ash and Tephra Menu] ...
[Report Menu] ...
