The high elevations of the Axial Zone (generally above 3000 m) are compensated isostatically by an increased thickness of the continental crust. For instance below the Maladeta massif, a root zone formed so that the Mohorovicic discontinuity is encountered there at a depth of 50 km. Likewise over most peaks of the Axial Zone, a negative gravity anomaly can be detected which slowly disappears to the east.