Geology
Lithology
Some of the largest structural units of the Iberian Peninsula are found within the Serra Gardunha, including the Hesperic massif, where the Central Iberian zone is integrated. This unit, also known as the Ancient Massif corresponds to an extensive area of ancient rocks, fractured and eroded, which represent esentially two complexes:
- The Schist-Greywachian complex corresponds to a grouping of metamorphic rocks with a sedimentary origin which is very uniform throughout the country, which is essentially made up of schists (material with more clay) and greywaches (more sandy material) The Schist-Greywachian complex is essentially located in the area of Souto da Casa, Castelejo and São Vicente da Beira.
- The hercinic granites, better known as Beiras granites are the most largely representative in Cova da Beira. The outcrop that embraces Fundão, Alcaria and the northern hillside is made up of a medium grain granite, sometimes fine, biotithic (grandiorite). On the surface the granites are very altered, with yellowy tone and they come apart very easily. (Silva & Gavinhos, 2002)
Lithological Map (in Graça & Santo, 1999)
Geomorphology
This unit presents the very different aspects between the moulded granite and the molded slate.
In the granitic terrain, the flat surfaces are preserved, interrupted by vigorous reliefs, with the inselbergs standing out, contrasting with the flat surfaces of erosion in the uplands or at the base of the mountain. There are other very common forms of moulded granite, like the caos de blocos and the tors (Silva et al, 2001).
Given the facility for rosion in the zone for granites and granitoides, they are moulded in a very characteristic way with rounded heads where the dense drainage networks originate (streams).
In the case of the schists and greywachians their shape is much more angular because they are more resistant to the action of erosive agents. This fact causes them to show up at higher altitudes, even though they are older than the other rocks.
With regard to the geomorpholoy of the Serra da Gardunha, we have to highlight some evidence of glaciations. Despite the fact that Gardunha is not subject to glaciar coverage, as was the case with Serra da Estrela, it is under the influence of intense cold (periglaciarism) during which the soil is frozen for a long time (permafrost). The temperature variations associated with the formation of ice, expand and contract the rocks causing their fragmentation into angular blocks.
This phenomenon is visible due to the innumerable deposits on the slopes (pebbles of schist and greywach) existent in the north hillsides of Gardunha (Silva & Gavinhos, 2002).