Soils developed on volcanic materials in the island of Thera, Greece

Samples were taken of soils formed on volcanic material, primarily composed of rhyodacitic pumice, on the island of Thera, Greece (South Aegean Sea, Southeastern Mediterranean), and analyses for physical and chemical properties carried out. These soils are characterised as having a coarse texture, low organic matter content, low cation exchange capacity (CEC) and soil moisture retention, but a high pH despite the acidic nature of the parent material. Extraction with sodium dithionite-citrate, acid ammonium oxalate, sodium pyrophosphate and hot 0.5 M NaOH showed that, in contrast to soils usually forming on volcanic material worldwide, soils lack noncrystalline minerals like allophane, imogolite, ferrihydrite and iron and aluminium humus complexes. The only noncrystalline mineral present and, in great quantities, is amorphous silica. Winds, prevailing practically all year round, transfer droplets of seawater to these soils which in combination with the great porosity, relatively high sodium content of the parent material and low rainfall are the primary factors in the poor development of these soils and high pH. No andic properties are apparent and, hence, these soils cannot be classified as Andisols. The major factors determining soil genesis on the island of Thera would appear to be the nature of the parent material and the climate.