The plateau of Aubrac is a volcanic massif (from 5 to 9 million years ago). The neck of Belvezet gives evidence of the former volcanic activity in this place. A volcanic neck (or volcanic plug) is a volcanic object created when magma hardens within a vent on an active volcano. Erosion removes the surrounding rock while the erosion-resistant neck remains.
The double neck of Belvezet is located on a hill above the hamlet of Belvezet. This basalt rocky hook is 8 million years old. At the top of it, a castle was built in feudal times : today, only a few ruins remain.