The Infiltration of Water Below Ground and the Concept of an Aquifer - Hydrogeology: Objectives, Methods, Applications - page 39

effective rainfall is greater. These resources can be found in the Rhodanian
(Miocene molasse of the Valence, Carpentras, and Valréas basins, Pliocene
molasse in Bresse) or coastal (“Astien” in Montpellier) plains.
4.5 Volcanic regions
Classic volcanic structures, consisting of an emission source and of lava
fl ows, combine a porous aquifer made up of high-capacity pozzolanas and
a fractured aquifer developed within lava fl ows, which rapidly drains water
from the cone towards springs at the foot the fl ow. These structures can be
found in the French Massif Central.
4.6 Limestone plateaus
Around the edge of the Massif Central, the Jurassic transgression deposited
limestone and marl onto an eroded Variscan platform. The resulting
limestone plateaus, known for their landforms and for their karst water
resources, can be found in the Vivarais, the Causses, the Quercy, in the Berry,
as well as in Charente and in Bourgogne. Cut apart by sometimes-deep
valleys (Ardèche, Tarn, Lot), they make up a mosaic of different aquifers.