Loading...
Debris-flow occurrence in granite landscape in south-southeast Brazil
Picanço, Jefferson Vieira, Bianca Martins, Tiago Gramani, Marcelo Faccuri, Gabriel Silva, Marcio
Picanço, Jefferson
Vieira, Bianca
Martins, Tiago
Gramani, Marcelo
Faccuri, Gabriel
Silva, Marcio
Citations
Altmetric:
Advisor
Editor
Date
Date Issued
2019
Date Submitted
Research Projects
Organizational Units
Journal Issue
Embargo Expires
Abstract
The widespread occurrence of Granite Massif landscapes in the Serra do Mar Range, south-southeast Brazil, is also connected with high incidence of debris-flow events. In recent years, the debris-flow events in Serra do Mar Range have caused many deaths and great infraestructure losses. These events occur in high gradient watersheds covered by a thin regolith. This paper intends to analyse the connection between debris-flows-prone watersheds and granitic regolith. These rocks, quite abundant along the mountain chain, are resistant to weathering, and present large vertical gradients. In addition, they generate porous and cohesive regoliths, which support infiltration to the rain water. When saturated, these regoliths can generate shallow landslides, which can liquefy and flow along channels, depositing this material in colluvial fans in piedmont areas. From this point of view, we analysed two watersheds in a granitic terrain, both of similar size and that recently suffered catastrophic events of debris-flows: 1) the Guarda-Mão creek watershed in Itaoca region, which had an intense meteorological event in January 2014; 2) the Gigante creek watershed, in Serra da Prata, which suffered an event with nucleation of debris-flows in March 2011. Both basins present themselves a thin regolith and rock outcrops in higher areas, grading to thicker regoliths and colluvium deposits in the foothills, where the gravels are deposited in the colluvionar fan. Both basins have soil densities (s) between 2.4 and 2.7 g/cm³, reflecting the presence of primary (quartz, feldspar) and secondary minerals (illite, kaolinite, montmorillonite and iron oxides). Both materials are porous (32% to 44%), with plasticity indices (PI) between 1% and 17%. Most materials have low plasticity, although the Gigante creek watershed is even lower, between 1 and 5%. The analysed watersheds are typical of granite/granitoid terrains in Serra do Mar Range, and present great similarity. Further studies should consider the morphometric characteristics of these basins, the mechanisms of rupture and the regoliths liquefaction processes, besides modelling the deposition in fan areas. This understanding could bring improvements to disaster risk management strategies throughout the Serra do Mar region.
Associated Publications
Rights
Copyright of the original work is retained by the authors.