A Morphological and Mineralogical Study of the Gray Hydromorphic Soils of the Hawaiian Islands!

Abstract

Gray hydromorphic soils are imperfectly to poorly drained soils that occur on the coastal fringes of the Hawaiian Islands on surfaces of Pleistocene to Recent age. Mottling is characteristic of the soils, and gley horizons occur in the more hydromorphic soils in the group . As the soils become hydromorphic, soil color values increase and structures deteriorate. Halloysite is the dominant clay mineral in the less hydromorphic soils and montmorillonite is dominant in the more hydromorphic soils of the group . The montmorillonite is iron-rich and in one soil has the formula (XO.74Ko.1l) (Si7.52Al0.48)^IV (Al1.85Fe1.60^3+MgO.35Ti0. l0 )^VI O20(OH)4. Hydrated halloysite occurs in all the soils studied, but it is most abundant in the more hydromorphic soils. Although the soils are derived from different alluvial materials, the trend of increasing montmorillonite and increasing hydrated halloysite with increasing hydromorphism is clearly related to the pedogenic processes operating in the soils. Similar mineralogical trends are found with increasing depth in each soil.