The hydrogeological massif is one of the types of hydrogeological structures of the continents , characterized in most cases by the development of free-flow fracture and fracture vein waters in fracture rocks, as well as in various intrusive formations of differentiated composition and age. This structure is also characterized by positive forms of relief : outcrops of the hydrogeological basin to the surface or only under a small layer of Quaternary sediments. Hydrogeological massif is a system of drainage of fissure and fissure-vein waters and waters of alluvial sediments.
There are several types of hydrogeological massifs depending on the rocks forming these massifs:
- folded by intrusive rocks (GM index)
- folded metamorphic rocks (index GMM)
- hydrogeological arrays composed of carbonate, volcanogenic or terrigenous rocks that form positive relief forms with anticlinal folding (GAM index)
- hydrogeological intermasses composed of carbonate, volcanogenic or terrigenous rocks forming positive relief forms with synclinal folding (GIM index)
A separate type of hydrogeological massif, called the Adartesian Basin (AAB index), which is characterized by negative landforms formed by folded sediments in the synclinal folds, can also be distinguished separately.