The Properties and Genesis of Four Soils Derived from Basaltic Ash, Mauna Loa, Hawaii

Abstract

The properties and genesis of four soils derived from basaltic ash are presented. In a sequence of increasing rainfall and elevation (decreasing temperature), there was a decrease in the values for pH, cation exchange capacity, the exchangeable bases, and base saturation. On the other hand, there was an increase in the values for carbon: nitrogen, clay percentages, free iron oxides, and the ratio of exchangeable calcium: exchangeable magnesium. There was also a general increase in the carbon content and in the values of the 15-bar water with increasing rainfall. In comparison with soils derived from andesitic ash, the soils derived from basaltic ash had high amounts of sand and silt, high pH values, and high base saturation for similar rainfall. They also had lower organic matter, carbon: nitrogen ratios, cation exchange capacity, and 15-bar water values. These differences are attributed to the younger age and to the higher contents of calcium and magnesium of the basaltic ash.