The main micromorphological characteristics of the fersiallitic soils on volcanic ashes in the Canary Islands are herein studied. Two groups of profiles are identificied. On one side, soils characterized by a high porosity, a predominance of round-shaped and small aggregates which compact themselves as the soil evolves, a lack of illuvial clay in the profil and a low alteration. On the other side, more compact soils with low porosity made out almost exclusively of fine contraction cracks, with total alteration and argillic horizon, where the illuvial clay has contributed almost 20% to its formation. The soils from the first group are considered the initial stage in the evolutionary sequence of the fersiallitic soils. They are young soils, slowly evolved both morphologically and chemically. The soils from de latter group are considered te final stage in this evolutionary sequence. They are old soils, highly altered and with a great morphological and geochemical evolution. The tendencies of alteration of the primary minerals and fragments of ashes are given on these soils, as well as the main processes which characterize the evolution of these soils. Finally, all profiles are classified according to the French and American classification.

Peer reviewed