Morphostructural aspects and erosion factors in coastal cliffs. The example of Pipa - RN

Abstract

In northeastern Brazil, cliffs occur in the rocks of the Barreiras Formation, which are composed of partially consolidated sediments. In the state of Rio Grande do Norte, Pipa beach, with its cliffs, is its main tourist attraction, receiving hundreds to thousands of people daily. The intense traffic of bathers at the base of the unstable cliffs, due to the consortium of internal hydraulic flow processes and wave action at the base, creates constant collapses, creating a high risk situation. In this technical note, the structural conditions of the cliff were evaluated, focusing on the characteristics of the outcropping layers, fracture planes, berm width and weathering and erosion processes associated with marine abrasion. For that, fieldwork was carried out with high resolution aerophotogrammetric surveys, description of scarp profiles and mapping of fracture sets. It was observed that vertical fracture planes, limited to the layers (Stractabounds), increased the permeability of the rock which led to leaching and the detachment of the blocks. Associated with this, the direct impact of the waves at the base of the cliff at high tide, opened an erosive indentation that removed the support of the underlying blocks, leading to collapse.