PROPERTIES AND CLASSIFICATION OF SELECTED VOLCANIC ASH SOILS FROM KENAI PENINSULA, ALASKA

Abstract

We studied properties and classification of selected volcanic ash soils formed under different vegetations on Kenai Peninsula, southcentral Alaska. Spruce (Sitka spruce) and alder soils had well-developed eluvial and spodic horizons common to most Spodosols. Fescue soil, developed under fescue-lichen tundra vegetation, showed a thick, very dark humus horizon similar to most Andisols in Japan. Bluejoint soil had an E horizon masked by organic matter, suggesting the degradation of Spodosol to Andisol. Although the four soils showed differences in vegetation and morphological properties, they shared many similarities in physical, chemical, and mineralogical properties, reflecting the properties of volcanic ash as the parent material. Nevertheless, the four soils had significant dissimilarities relating to their soil-forming processes. For example, spruce and alder soils showed humus and mineralogical characteristics, such as high humic-acid-to-fulvic-acid (HA:FA) ratios and abundance of smectite in the eluvial horizons and very low HA:FA ratios and abundance of chloritized 2:1 minerals in the illuvial horizons. Fescue soil contained humic acid with a high degree of humification and allophanic clay mineralogy. Bluejoint soil was nonallophanic as spruce and alder soils, but it showed the predominance of chloritized 2:1 minerals in the clay fractions throughout the profile. Both spruce and alder soils having well-developed eluvial and spodic horizons satisfied the chemical criteria for a spodic horizon and were classified as Typic Cryohumod (Soil Taxonomy). Although the two soils also satisfied andic properties, we insisted that the Andisol-Spodosol transition problem should be basically brought into settlement according to the properties reflecting the major soil-forming processes. Fescue soil satisfied the requirements of andic properties and was classified as Dystric Cryandept (Soil Taxonomy) and as Typic Haplocryand (ICOMAND proposal). Bluepoint soil had a less developed eluvial horizon, but satisfied the chemical spodic criteria using the clay contents determined by the NSSL pipette method because of incomplete dispersion of the clay fraction. However, according to the data of clay measurement by the pipette method after sonication and pH adjustment, bluejoint soil did not meet the spodic criteria and was classified as Dystric Cryandept (Soil Taxonomy) and as Typic Alicryand (ICOMAND proposal). A method of particle-size analysis should be established for volcanic ash soils, especially for the spodic criteria of (Fep + Alp)/% clay.