Evolução morfológica das falésias fluviais da margem direita do Rio Negro – Iranduba, AM

Abstract

This study investigates the morphometry and evolution of river cliffs along the right bank of the lower course of the Rio Negro, in Amazonas. River cliffs are described as steep formations that develop along the banks of large rivers in the Amazon region. The main objective was to analyze the morphology and evolution of the cliffs, focusing on their physical characteristics and alteration processes. The specific objectives were to characterize the morphology of the cliffs, describe the main processes, mechanisms and features of physical alteration, and measure the evolution of the cliffs over time. The research was conducted at five different points along the right bank of the Rio Negro, where detailed field observations and morphological analysis of the cliffs were carried out. Mapping, sediment analysis and monitoring of hydrological conditions were used to obtain data on the morphometry and alteration processes of the cliffs. The cliffs have various morphological characteristics that vary along the right bank of the Rio Negro. The formation of ducts (resulting from biological action) and grooves in the walls, resulting from surface water runoff during periods of rain, were observed. Some cliffs show exposed escarpments with sparse vegetation and different stages of laterization, while others have collapsed blocks at the base due to water erosion. The main erosive processes impacting the cliffs include fluvial erosion, undermining of the base and mass movements. The fluvial action of the Rio Negro, especially during periods of flooding, exerts significant pressure on the base of the cliffs, causing undermining and removal of material. Rainwater infiltration contributes to soil saturation and the occurrence of landslides. The evolution of cliffs over time is influenced by factors such as the composition of the material, fluvial and pluvial action, and the dynamics of mass movements. The presence of clayey and sandy soils and laterite crusts varies between the sites studied, influencing the cliffs' resistance to erosion. Evidence of undermining during the Rio Negro's flood and ebb events indicates the continuous alteration and instability of these formations. This study highlights the importance of understanding the morphometry and erosion processes of the fluvial cliffs on the right bank of the lower course of the Rio Negro. Morphological variations and the composition of the material significantly influence the cliffs' resistance to erosion, contributing to their retreat (loss of sediment). A detailed understanding of the morphometry and evolution of river cliffs contributes to geoscientific knowledge of the Amazon region and provides information for planning and mitigating environmental risks associated with erosion and landslides.