Volcanic Soil Resources in France

In continental France, volcanic soils cover about 6000 km

2

, mostly in the Massif Central (>5000 km

2

), but also in small area of Vosges and Morvan. Most of these soils are Andosols, although there are also Cambisols (Brunisols) and exceptionally Podzols.

The volcanic soils distribution is fairly well related to the present climato-topo-sequence, as well on recent pyroclasts as on old volcanic or basic metamorphic formations.

The key factor for Andosols occurrence is the climate, and notably udic or perudic moisture regimes. The chemical composition of parent rock has rather weak influences on the soil genesis, except rhyolitic materials, which favour Podzol formation. However, the age of parent rock is important. The Silandosols are related to recent pyroclastics on the Chaîne des Puys. Aluandosols have formed on older compact lavas, but their effective parent material is often a loose pre-weathered volcanic or basic metamorphic material. Their final development occurred during Holocene. The anthropic effects on soil transformation, except erosion or alteration of soil surface properties, are not obvious.