Assessment of the susceptibility to gravitational instability of cliffs on the southern coast of Rio Grande do Norte from the perspective of the Erosive Susceptibility Index (ISE)

Abstract

Coastal cliffs are steep escarpments formed by the integrated action of marine and subaerial processes, seen in several areas along the Brazilian coastline. The rise in relative sea level and the intensification of coastal dynamics contribute to the retreat of these landforms and to the increase in susceptibility to mass movements, especially in areas with human occupation near their base. In this context, this study carried out an assessment of the susceptibility to gravitational instability of cliffs on the southern coast of Rio Grande do Norte, from the perspective of the Erosive Susceptibility Index (ISE), based on field data collected at three representative beaches—Cotovelo, Tabatinga, and Cacimbinhas—where a proposed methodology was applied using four main parameters: vegetation cover, anthropogenic influence, lithological friability, and structural instability conditions.The results indicated that, although the areas present similar geological and vegetation characteristics, the intensity of human occupation was one of the main factors differentiating susceptibility levels, and it was observed that wave action, combined with high material friability, the presence of fractures, and human interventions, enhances instability processes, resulting in susceptibility levels ranging from moderate to high. Therefore, continuous monitoring and coastal planning aimed at risk mitigation are necessary.