Estudo da estabilidade geomorfológica das falésias de Carro Quebrado, litoral norte de Alagoas

Abstract

The present study on the geomorphological stability of the cliffs of Carro Quebrado beach, located on the northern coast of Alagoas, in the municipalities of Barra de Santo Antônio and Passo de Camaragibe, approximately 50 km from Maceió, investigates these morphologies formed by marine erosion processes and superficial morphodynamic processes. These cliffs play a significant role in coastal protection and ecosystem services. The analysis was carried out on a stretch of approximately 4.2 km, consisting of steep and stepped cliffs, both active and inactive. Potential geomorphological risks were identified and quantified in relation to the processes of land use and occupation on the cliffs of the beach. In addition to geomorphological characterization, land use and occupation mapping, classification of the morphodynamic stability of the cliffs, and classification of potential geomorphological risk levels based on local morphodynamic characteristics and current and potential land use forms were conducted. The first stage of the study involved a literature review and theoretical foundation on topics related to cliffs structured in the Barreiras Formation, land use and occupation in these areas, and associated geomorphological risks. The methodological procedures for geomorphological characterization included data collection, field analysis, GIS processing, and the creation of a cartographic model with sectorization of the area. Land use and occupation were mapped based on 2024 images from Airbus, processed in QGIS to identify land use classes and understand their impact on the cliffs. For the classification of morphodynamic stability, two methodologies were applied: the analysis of the Instability Hazard Index (IHI), which involved identifying the factors causing instability, assigning weights and scores, calculating the IHI, and producing the instability map; and the quantitative analysis of cliff retreat between 2002 and 2024. The identification and classification of geomorphological risks were divided into two parts: the first involved analyzing rupture mechanisms and mass movements, and the second involved mapping and characterizing risk areas. With the results obtained, it was possible to characterize the area into three sectors: North, Central, and South, each with specific characteristics reflecting the natural dynamics and environmental conditions of the landscape. The land use and cover mapping enabled the identification of seven classes: dense vegetation, low vegetation, sugarcane, pasture, exposed soil, buildings, and water bodies. The central sector exhibited, in the 10-meter strip from the edge, the highest concentration of the classes most susceptible to erosion risk, with exposed soil covering 46.14% and sugarcane 26.38% of the total area. The IHI results for the North and Central sectors revealed that they had the highest levels of instability, with very high hazard classes, 15% (836,821 m) in the North sector and 16% (904,191 m) in the Central sector. Additionally, these sectors showed areas with high hazard, representing 15% (399,202 m) in the North and 7% (199,326 m) in the Central sector. The cliff retreat rate was 51,554.873 m², with the greatest retreat occurring in the North sector (1,268.43 m²) due to marine abrasion. The South sector, with inactive cliffs, showed the lowest retreat rate. The identification of geomorphological risks indicated that the North and Central sectors had more erosive features and records of mass movements. The delineation of risk areas highlighted very high-risk locations at the base of the cliffs in the North sector and at the top and base of the cliffs in the Central sector. It is expected that the results will help highlight a topic that has been little explored in the state, contribute to future studies, and, if adopted, support decision-making by the government and productive sectors of coastal regions.