Spatiality and evolution of the incision of river valleys from the relief dissection in the staggered steps of the southeast of minas gerais - Brazil

Abstract

The geomorphological configuration of the southeast of Minas Gerais is made according to staggered steps. The spatial organization of these steps closely accompanies the spatial distribution of the hydrographic basins of the area investigated in this work, such that the upper step is drained by the basins of the Paraná and São Francisco rivers (inland basins) and the lower by the river basins Doce and Paraíba do Sul (coastal basins). The coastal basins present greater denudational capacity because of their greater altimetric amplitude and because they are directly linked to the general base level of the ocean. The present work investigated the dissection and spatial evolution of the fluvial valleys in the different geomorphological compartments in which these sets of basins are inserted. A research method was used to investigate the dissection of the relief and incision of the river valleys supported by geoprocessing techniques and the analysis of geocartographic attributes. The results showed that the evolution of the river valleys is conditioned by the different degrees of incision of the hydrographic network and that the incision is larger in the coastal basins. This condition is a relevant explanatory factor regarding the recurrence of stream piracy already recognized in the geomorphological literature, which are responsible for the incorporation of stretches of the inland basins to those coastal basins. In the coastal basins, the most effective vertical incision of the hydrographic network resulted in the significant deepening of the valleys and, consequently, in their higher altimetric gradient and amplitude and in the narrowing of their flanks. This geomorphological condition in the area investigated favors the installation of destabilizing processes of the slopes, since its dynamics is linked in space and time to the rhythm and force of the incision of the hydrographic network. In these interior basins the lower altimetric amplitude of the valleys favors the accumulation of sediments that are transported in the fluvial channels.