Volcanic Ash-Influenced Soils

Northwest soils are complicated by the frequency of volcanic eruptions in the Pacific Northwest region prior to and during the Holocene.   Horizon sequences in tephra-influenced soils may consist of multiple tephra deposits that differ in age as well as mineralogy, chemistry, and degree of weathering.   The most recent depositions of Mount St. Helens and Mount Mazama have influenced north Idaho soils. 

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