Poço do Inferno (Geosite), Manteigas

More than 300 million years ago, during a long period of tectonic plate collision, granitic magmas installed at depth. This intrusion of magmas at high temperature led to the overheating of the surrounding rocks, recrystallizing their minerals and creating a new harder and more resistant rock. The process is called contact metamorphism and is comparable to the of baking clay to make it more resistant. In Poço do Inferno, this process can be observed by the presence of hornfels, very hard rocks that form rugged peaks that stand out in the landscape. Over geological history, granites and hornfels underwent tectonic stresses and the chemical action fluids, including groundwater. Granites are more easily weathered, while the hornfels because of their mineralogical and structural characteristics, are much more resistant to weathering and remain fresher. Once at the surface, due to the fluvial incision of the Leandres stream, the granites are quickly carved, while the hornfels hamper the linear fluvial erosion. In this struggle between the water, hornfels and granites, the hornfels resistance prevails, while deeply weathered granites are eroded. The result is the formation of vertical rock walls where current waterfalls develop.

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