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Erosão fluvial sobre rochas vulcânicas: algumas inferências a partir de segmentos côncavos de perfis longitudinais

2012; Sociedade Brasileira de Geologia; Volume: 42; Issue: s1 Linguagem: Inglês

10.5327/z0375-75362012000500004

2177-4382

Adalto Gonçalves Lima,

Geography and Environmental Studies

The research sought to identify factors that control the homogeneity of the resistance to fluvial erosion over volcanic rocks, which lead to the formation of concave segments in the longitudinal profiles of rivers. Through cartographic and field surveys of geological and geomorphological data, and using the slope-area relationship, we investigated the role of lithological characteristics and tectonic fracturing in the formation of concave segments in a small channel installed in the basalts and rhyodacites of the Serra Geral Formation, in Parana State, Brazil. The slope-area relationship in the form of a power function identified the existence of continuous and discontinuous concave segments, that is, segments interrupted by reaches whose slopes are not adjusted to the others. The concave segments investigated are carved in vesicular basalts and rhyodacites due to the lower resistance to erosion of these rock types. The insertion of the channel in fractured zones improves the slope adjustment of the concave segments, resulting in an increase in the coefficient of determination (R2). The index of concavity is -0.79 in rhyodacites and -1.05 in the vesicular basalts. Although this difference may be due to non-tectonic fracturing of rhyodacites, it suggests that the vesicular basalts are less resistant to fluvial erosion.