Andosols are azonal soils developed on volcanic deposits and are found in all climates and at all altitudes in volcanic regions all over the world. The total Andosol area is estimated at some 1.1 million km2 or less than 1 of the global land surface. Andosols are characterised by the presence of either an andic horizon or a vitric horizon. An andic horizon is rich in allophanes (and similar minerals) or aluminium-humus complexes whereas a vitric horizon contains an abundance of volcanic glass.

Andosols typically have a dark humic A horizon on top of a brown B- or C-horizon. Topsoil and subsoil colours are  distinctly different. The average organic matter content of the surface horizon is about 8 but some varieties may contain as much as 30 organic matter. The surface horizon is very porous and the good aggregate stability of Andosols and their high permeability to water make these soils both fertile and relatively resistant to water erosion.

Other international names are Andisols (Soil Taxonomy), Vitrisols (France) and volcanic ash soil.

Large continuous areas with Andosols of Europe are found in the Massif Central of France, in the North-Eastern Carpathians in Romania and in the coastal volcanic areas of Sardinia and continental Italy.

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