Analysis of erodibility conditions on the cliff in Ponta Verde beach at São José de Ribamar municipality in Maranhão state (Brazil)

Abstract

Cliffs are geomorphological features characterized by steep slopes and constitute approximately 80% of coastlines worldwide, demonstrating their significance for study. In the municipality of São José de Ribamar located in Maranhão state, there is a unique set of cliffs of Tertiary-Quaternary sedimentary origin, subject to marine erosion. Because the study area is experiencing increasing human occupation, the research aimed to analyze the main physical soil properties which influence the erodibility of the Ponta Verde beach cliffs and their consequences for the local ecosystem. The procedures adopted consisted of field work, with sample collection to determine the principal physical characteristics of the soils on the cliff, such as soil density, morphological analysis (color, structure, consistency, texture), measurement of infiltration rates, photographic recording with a drone, and laboratory analysis of erodibility parameters. The results indicated that the soil at the top of the cliff is compacted, with a predominantly sandy texture, which influenced infiltration rates and high friability, favoring the occurrence of mass movements, such as landslides, and erosional features, such as ravines on the cliff slope. The combination of these erodibility factors and rising sea levels leads to the retreat of the cliffs in this part of São José de Ribamar municipality, resulting in environmental problems and limitations to its urban expansion.