The karst phenomenon is widespread a lot on the area of the Sirente Velino Park. As a matter of fact, it is frequent to meet chasms, caves, and dolines, all this shows of how this phenomenon is still particularly active.

Among the various karst events, the chasm of Terranera is of a considerable interest in the closed basin of Rocca di Cambio, known as Pozzo Caldaio where the waters of the plain disappear, and then reappear, further east, in the resurgences of Stiffe Caves, rich of calcareous concretions of special effect and under a landscape bond.
From the cave, which is reached from the hamlet of Stiffe, in the municipality of S. Demetrio nei Vestini, the water comes out in a wild environment with significant jump and rocky crags, covered with grass and shrub vegetation of major evocative visual and sound effect.
The waters themselves, thus enrich the Aterno River that crosses the AternoValley and the Subequana Valley.

Compared to the phenomenon of karst, undoubtedly unless extended, is that of river erosion. But certainly no less spectacular, with The Celano Gorges, approximately 5 km long, in many sections very narrow, and with vertical faces often higher more than one hundred meters. This real canyon, carved by the river La Foce, in The Arano Valley, at 1,300 m, southeast of Ovindoli, is also under a landscape bond. The stream, crossing on the bottom of the canyon, is rich of water in the springtime.
The steep faces of the gorges, tens of meters high, are a characteristic habitat rupicolo, where there are varies vegetation and where different species of birds nest.