the frequency with which the upper end of a valley assumes the form of a semicircle of precipitous cliffs, called a cirque.

The highest waterfall is Gavarnie (462 m or 1,515 ft), at the head of the Gave de Pau; the Cirque de Gavarnie, in the same valley, together with the nearby Cirque de Troumouse and Cirque d'Estaubé,