CHARACTERISTICS AND CLASSIFICATION OF VOLCANIC-ASH-DERIVED SOILS IN ALASKA

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Abstract
Twenty pedons of volcanic ash soils from southern Alaska used in this study have a cryic temperature regime and udic to perudic moisture regimes. They have distinctive morphological properties common to Andisols in many other parts of the world: (1) multisequum with abrupt or clear boundaries, (2) very friable granular structure in A horizons and friable subangular blocky structure in B horizons, and (3) loamy texture with a smeary consistency. They also have distinctive morphological properties common to Spodosols: (1) an organic horizon in all the pedons, (2) an albic or E horizon in most pedons, (3) underlying the E horizon, one or more horizons with hue redder than 10 YR in most pedons, and (4) a placic horizon below the spodiclike horizons in some pedons. The physical and chemical properties of the 13 pedons are presented and discussed. The properties of 7 pedons presented in previous studies are reviewed. All 20 pedons were found to meet the criteria of andic properties, and 19 of them also meet the chemical criteria of a spodic horizon. The pedons were classified according to both Soil Taxonomy and the Andisol proposal. Andisols were proposed to be keyed out after Histosols, but before Spodosols (Leamy 1988). Those Andisols having chemical properties of spodic horizon are differentiated from Spodosols by not having an albic-spodic sequum within the required thickness of horizons with andic properties. A comparison of the two classifications and the implication for soil survey and interpretation are also discussed.
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