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Geology in Sobrarbe

Karstic landforms

Carbonate rocks, limestone and dolomite among others, can be easily dissolved by rain water if it contains carbonic acid. In Sobrarbe, landscapes formed by carbonate rocks are predominant, especially the Cotiella massif and the Monte Perdido massif, the highest limestone massif in Europe. Karstic landforms are also present in the Castillo Mayor and the Peña Montañesa Rocks..

Outer karstic formation in the Armeña Cirque. (Image by Carles Pons, ACEC).

The surface of a karstic landscape is recognisable by its lack of surface water and the typical irregularities of the terrain: karren, sinkholes, foibes, poljes, etc. But the most breathtaking landforms are caves with stunning speleothems in the limestone massifs in Sobrarbe, some of them are known world-wide.

• Arañonera System.
  Eastern area in the Tendeñera Mountain Range (municipality of Torla).
• Sima C-9 in the Torrente de la Payón.
  In the Sucas Mountain Range (municipality of Puértolas).
• Casteret Cave.
  In the SW base of the Casteret summit, in the area of Marboré (municipality of Fanlo).
• Escuaín Springs System.
  In the Sucas mountain range massif, between the Gurrundué cirque and the Angonés Gorge (municipality of Tella-Sin).
  
• Moros Cave.
  In the Añisclo Valley, by the confluence of the Aso and Bellós Rivers (municipality of Fanlo)..
• Punta de las Olas System.
  At the SE of the Monte Perdido Massif (municipality of Fanlo)..

The Moro Cave. Several sinkholes and caves form the subterranean landscape in the Geopark.

The caves include rock formations created by the persistent dripping of water (speleothems). When the solution reaches an air-filled cave (zone of aeration), a discharge of carbon dioxide may alter the water's ability to hold minerals in solution, causing its solutes to precipitate as calcium carbonate (calcite). Stalactites are speleothems that hang from the cave ceiling and are formed where water seeps through the cracks. Stalagmites are their "ground-up" counterparts. With enough time, both stalactites and stalagmites can meet and form a Column.

Sinkhole A-88. (Image by Carles Pons, ACEC).

Karst fensters are another kind of stunning karst formation. The thermal spring in Puyarrueyo, the springs in the Escuaín Valley and the spring in Tella, near the cave of the cave-dwelling Bear Cave (Ursus spelaeus) stand out. Along the upper course of the Irués River, we find the Fornos Spring and the intermittent Chorro..

Most caves are only accessible to expert speleologists who are trained to go into deep sinkholes and narrow passages. However, there are some exceptions, like the Moros Cave, in Molino de Aso, and the Manatuero and Malapreciata caves, near Buerba..

The largest karstic systems are found in the N and NW of Sobrarbe County, in three different stratigraphic levels:

• (1) Devonian-Carboniferous
• (2) Cretaceous-Paleocene and
• (3) Eocene.

To ensure the preservation and promotion of the karstic heritage in Sobrarbe, the Geological Park of the Pyrenees cooperates with its speleological research and promotion. As a consequence of this partnership, the itinerant exhibition "COTIELLA, the Sea of Stones" was opened in Plan on 6th December 2008, summarizing 40 years of research into karstic landforms in the Cotiella Massif.

Panel of the exhibition produced by the Scientific and Speleological Cotiella Association.