Geossítio 12 Serlei sinks
Curious shapes on the mountain plateau…
The Serra da Freita granite outcrops on the Serra da Freita plateau along an extensive strip. The granite landscape is marked by a number of curious shapes, from rounded blocks that often form a “chaos of blocks”, to detailed shapes such as “sinks”. In the Serlei region, in the upper part of the granite blocks, there are numerous circular concavities known as sinks. It is probably the region of the Serra da Freita where we find the largest number of these geoforms, whose formation is related to the natural action of the wear and erosion of the rocks, particularly by the action of water.
While walking along the 17 km long circular PR15 geotourist footpath, we came across the Pias do Serlei geosite.
Informação Geológica
On the higher tops of the residual granite reliefs of the Freita mountain range, there are often numerous alveolar forms on their surface, known as pias or gnamas. Sinks are small sub-circular to elliptical depressions which can, however, have more complex shapes due to the coalescence of individual sinks. They vary in diameter from around 30 cm to 1 m, in the latter case when coalescence occurs.
The genesis and evolution of these granite microforms point to a polyphase origin. Initially, they may have developed under the mantle of alteration, clearly reflecting the irregular penetration of the alteration front, which gave rise to a whole series of irregularities in the rock surface. After the exhumation of this surface, the sinks would have developed along these irregularities, preferential places for receiving and accumulating water. Water is the essential factor in the evolution of these geoforms as it promotes hydrolysis, hydration and mineral dissolution reactions, causing differential weathering on the alteration front, as well as the growth and differentiation of the sinks after their sub-aerial exposure. At the Pias do Serlei geosite, there are numerous granite blocks where multiple sinkholes are present, with varying degrees of development, making it possible to analyze the stages of their evolution.
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Natura 2000
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