Properties and Classification of Three Volcanic Ash‐derived Pedons from Aleutian Islands and Alaska Peninsula, Alaska

Abstract Three soils formed from volcanic ash on the Aleutian Islands and adjacent Alaska Peninsula were characterized and classified according to Soil Taxonomy to test some of its recent revisions. All three soils have bulk density <0.9 Mg M −3 , acid‐oxalate extractable Al of 15 to 25 g kg −1 , phosphate retention >90%, and sand fraction dominated by volcanic glass. These properties meet the andic soil properties and qualify for the provisional Andisol order as defined by the International Committee on the Classification of Andisols (ICOMAND). However, two of the three pedons also meet the laboratory criteria for Spodosols. Soil colloids of all the pedons are allophanic, showing the predominance of allophane and Al‐humus in the surface horizons and that of allophane in the subsurface horizons. Laminar opaline silica is present in the surface and subsurface horizons. This fact strongly suggests that concentration of silica by freezing of soil solution is a process for the formation of laminar opaline silica in the subsurface horizons having highly reactive Al. Chloritized 2:1 minerals are found to be major crystalline clays throughout the profiles of all the pedons. In addition, zeolite is present in one pedon, indicating that the parent ash contains hypothermally altered material. The apparent overlap in the definitions of Spodosols and the provisional Andisol order is also discussed.