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Humods in Relation to Volcanic Ash In Southern Alaska
Author(s) -
Rieger Samuel
Publication year - 1974
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1974.03615995003800020036x
Subject(s) - podzol , weathering , volcano , geology , horizon , volcanic ash , geochemistry , mineralogy , soil science , soil water , earth science , mathematics , geometry
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.