Geoparque Unesco

Periglacial Landforms

Stratified debris in La Selva Gorge

Stratified debris in Old Sobrarbe
Municipality: Bárcabo

In Bárcabo, between Arcusa and Eripol, we find different outcrops related to periglacial morphology. One of the best examples is located in La Selva Gorge, on the eastern side of the A-2205 road, south from the detour towards Sarsa de Surta, near the border of the Sierra and Cañones de Guara Nature Reserve.

Arranged debris of angular fragments of sedimentary rocks.

Geological Context

The gelifraction process (a kind of fragmentation) of the rocks is related to the freeze-thaw alternation caused by water filling the pores and crevices in the rocks, causing their fragmentation. In this way, rock fragments are deposited (gelifracts or crioclasts) on the side of the mountains. The fall and accumulation of these fragments form screes, altthough in periglacial areas (where it freezes intensely and there are thawing seasons without snow) stratified debris can also be formed..

Stratified debris indicates that water from ice or snow fusion has transported and arranged gelifracts, forming scarcely consolidated strata in general.

Geological Signifiance

The location of this outcrop shows that the periglacial domain stretched south of the high Pyrenean valleys, in an area far away from the glacial domain.

Although their origin is still uncertain, these materials reflect a periglacial dynamics. The rock fragments are of different sizes, from gravel to large scattered blocks, with a minor clay and limestone matrix irregularly distributed. There is a certain arrangement in these irregular strata, with frequent surface erosion..

Avda. Ordesa 79. 22340 Boltaña. Huesca. 974 518 025.