The valley bottom at Figarella, ca. 8 km south of Calvi, offers a good view on a volcanic highlight of Corsica, the ring dyke of the Monte Cinto caldera.
The stop is located exactly at the position, where the dyke is cut by the Figarella valley. From here, the ring dyke appears as a steep, very prominent ridge running perpendicularly to the valley. Towards the southeast, we can see the volcanic rocks in the center of the Monte Cinto caldera, which forms the upper part of a large Variscan batholite.
During a large volcanic eruption, when the magma chamber below a volcano empties itself by giving off its magma to the surface, pressure in the chamber decreases. This can lead to tensile fractures in the rocks above the magma chamber. Once these fractures propagate into the chamber, the entire overlying volcano may collapse into the chamber, so that magma is further expelled into the fractures, thus giving birth to the ring dyke. The surface expression of such an event is a large, subsided circular area in the region of the volcano.