Análise geomorfológica da voçoroca do Mombuca (Monte Carmelo - MG)

Abstract

The tropical conditions in Brazil promote the occurrence of water-induced erosion, which generates linear features such as gullies, especially in areas composed of fragile geological materials. In the Monte Carmelo region (MG), significant linear erosive features are recorded in areas of rocks and regoliths associated with the Monte Carmelo Complex. For instance, near the urban area of this municipality, there is the Mombuca gully, located in the geomorphological compartment of the Dissected Plateaus of Alto Paranaíba, which connects to the Mombuca stream, a tributary of the Perdizes River. The study aimed to evaluate the erosive dynamics of the Mombuca gully using cartographic products generated from images captured by Remotely Piloted Aircraft (RPA), along with the installation of monitoring stakes and the evaluation of material characteristics. The developed methodology followed the stages of Pre-Field, Field, and Post-Field. In the first stage, bibliographic surveys, flight plans, and the planning of locations for stake installation were carried out. During the Field stage, RPA flights were conducted for the scenarios of Oct/2022, May/2023, and Feb/2024, along with monthly monitoring of the stakes and morphological descriptions of profiles and trenches, with the collection of soil and saprolite samples. The third stage, Post-Field, included processing the acquired images to generate base and thematic maps, together with tabulating the values obtained from the stakes and granulometric and morphoscopic analyses in laboratories. From the RPA images, the following maps were generated at a 1:7,000 scale: Cartographic Base, Digital Terrain Model, Hypsometric, Slope, and through photo interpretation of the images from the three scenarios, a detailed Geomorphological Map was produced. This map identified the following compartments: dissected area (1.1), slopes leading to the gully (1.2), residual forms connected to the slopes leading to the gully (1.3), residual forms not connected to the slopes (1.4), and accumulation of floodplain and fluvial terraces (Aptf, 1.5). Within these compartments, the types of running waters and their incision patterns, topographic data, denudative features, and anthropogenic models were detailed. Three erosive channels constituting the gully were observed, with significant evolution, totaling approximately 163,250.60 m³ of lost sediments. One of the channels, referred to as number 3, has a smaller volume due to its partial infill by technogenic deposits, observed in images and confirmed during field activities. Over a year (Feb/2023 to Feb/2024), punctual changes in the distances of the monitoring stakes were evidenced, with emphasis on stake number 6. Around the stakes, the presence of regressive features and edge deposits was also noted. Granulometric analyses demonstrated a considerable presence of the sand fraction in the composition of Cambisols, with values around 40%, while morphoscopic analyses indicated that the coarse fraction is predominantly composed of quartz, originating from the granites of the Monte Carmelo Complex. It is understood that the erosive dynamics of the Mombuca gully are regulated by tropical climatic conditions associated with the characteristics of the fragility of the constituent materials, as well as more recently influenced by anthropogenic actions.