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This article in SSSAJ

  1. Vol. 43 No. 3, p. 541-547
    Received: Aug 8, 1977



Physical, Chemical, and Mineralogical Characteristics of Soils from Volcanic Ash in Northern Idaho: I. Morphology and Genesis1

  1. M. A. Fosberg,
  2. A. L. Falen,
  3. J. P. Jones and
  4. B. B. Singh2



Mission soils, coarse-silty, mixed, frigid Andic Fragiochrepts, are representative of volcanic ash soils found extensively in northern Idaho, northeastern Washington, and northwestern Montana. They have developed under a western hemlock (Tusuga heterophylla) habitat type with 740 mm of precipitation, > 8°C mean summer soil temperature and 7.5°C mean annual soil temperature (weather data, Univ. of Idaho. Res. Stn., Sandpoint). The B2ir or cambic horizons have developed from volcanic ash and the underlying IIA'&B' and IIB'2x horizons have fragipans developed in glacial outwash sediments. Horizons from volcanic ash have higher values of estimated allophane, organic C, extractable Fe, Al, and Mn, exchangeable H, 1/3- and 15-bar moisture, and CEC than do underlying horizons. Bulk densities range from 0.80 to 0.90 in volcanic ash horizons compared with 1.41 to 1.65 for glacial sediments. X-ray patterns show little indication of crystalline minerals in the ash-related horizons. Concretions have greater contents of Mn and Fe whereas Al remains relatively constant in relation to the total soil. Development of a B2ir, without an Al horizon under the O horizon, is characteristic of soils associated with these climatic and vegetational zones. Diagnostic properties make the cambic gradational to a spodic horizon.

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