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Transported trees from the 1982 Mount St. Helens sediment flows: Their use as paleocurrent indicators

Sedimentary Geology
Publication Date
DOI: 10.1016/0037-0738(85)90073-9
  • Earth Science


Abstract Sediment flows resulting from the 1980 and 1982 eruptions of Mount St. Helens, Washington, transported and oriented numerous stumps and logs. Counts taken soon after the 1982 eruption on unaltered portions of the sediment flow provide meaningful statistics for comparison with fossil wood deposits. Of the transported stump and log population, 4–13% was deposited as upright stumps and 78–94% as horizontal logs with a few diagonal and upside-down stumps. The horizontal logs were oriented parallel to the river channel, showing that trees can be good paleocurrent indicators. Features useful in differentiating transported stumps from in-situ ones are a wide root system (trunk/root ratio <1), short broken trunks, broken large roots, and a low percentage of upright stumps in relation to horizontal logs. The oriented horizontal logs, transported vertical stumps mixed with trees buried in place, and sedimentology of the flows aid in interpreting fossil wood deposits such as the Yellowstone “fossil forests”.

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