Humods in Relation to Volcanic Ash In Southern Alaska1
- Samuel Rieger2
Analyses of Spodosols in southern Alaska indicate that Humods—well-drained Spodosols in which the free iron-carbon ratio in at least part of the spodic horizon is less than 0.2—apparently form only in ashy materials, though not all Spodosols developed in volcanic ash are Humods. Spodosols formed in other materials may have similar morphological properties, but all have narrower ratios and are classified as Orthods. The distribution of the two groups of soils in this cool, humid area is apparently not dependent on differences in precipitation rates, temperatures, or vegetative cover. Wider Fe/C ratios in the ashy Spodosols result from lower concentrations of free Fe rather than from larger accumulations of illuvial C in the spodic horizon. A possible reason for the affinity between low-iron Spodosols and ashy parent materials is a more ready availability of aluminum from volcanic ash as opposed to the more rapid release by weathering of iron in other materials.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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