The assessment of soil chemical, physical, and structural properties as landslide predisposing factors in the Serra do M
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ORIGINAL PAPER
The assessment of soil chemical, physical, and structural properties as landslide predisposing factors in the Serra do Mar mountain range (Caraguatatuba, Brazil) Rodrigo I. Cerri 1 & Vania Rosolen 2 & Fábio A. G. V. Reis 1 & Augusto José Pereira Filho 3 & Felipe Vemado 3 & Lucilia do Carmo Giordano 1 & Beatriz Marques Gabelini 1 Received: 3 July 2019 / Accepted: 26 March 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Landslides have environmental, social, and economic impact in the Brazilian Atlantic coast (Serra do Mar). In addition to meteorological, geological, and geomorphological settings, mineralogical and pore space heterogeneities in soil covers are considered important characteristics that can influence landslide occurrence. Since soil covers are very clayey, the evaluation of macro- and micromorphological soil features (soil structures, soil materials, and pores) resulted by mass movement during slope instability is difficult. This field of investigation practically does not exist in the Serra do Mar. The objective of this paper is to analyze the soil cover in a toposequence to identify macro- and microscopic soil features resulted from landslide processes, and assess the role of pedogenesis on landslide development. Macro- and micromorphological approaches were used to study the architecture of the soil cover and soil was sampled to determine chemical and mineralogical composition by XRF and XRD. Undisturbed clods were used to determine pore size and pore compartment by mercury porosimetry. It was recognized a brecciated and an undulating parallel-striated fabric. Both features were generated from mass movement and were unclear in the clayey horizons in the bottom of the toposequence. In this level, the occurrence of mottles suggesting short-term soil saturation and the presence of micropores < 1000 nm in soil could be the factors that drive soil movement downslope. Keywords Landslide . Soil cover . Soil mottles . Weathering profiles . Serra do Mar
Introduction Serra do Mar mountain range in Brazil is one of the most sensitive areas to mass movement, such as landslides and debris flows, during the rainy season. In 1967, hundreds of landslides and several debris flow reached Caraguatatuba (São Paulo State), in which 120 people died, and 400 houses were * Rodrigo I. Cerri [email protected] 1
Department of Applied Geology, Institute of Geosciences and Exact Sciences, São Paulo State University (Unesp), 24A Avenue, 1515, Bela Vista, Rio Claro 16506-900, Brazil
2
Department of Petrology and Metallogeny, Institute of Geosciences and Exact Sciences, São Paulo State University (Unesp), 24A Avenue, 1515, Bela Vista, Rio Claro 16506-900, Brazil
3
Department of Atmospheric Sciences, Institute of Astronomy, Geophysics and Atmospheric Sciences, University of São Paulo, Matão Street, 1226, São Paulo 05508-090, Brazil
destroyed (Cruz 1974). Approximately 4,200,000 m3 or 7,560,000 ton of materials was displaced from Santo Antônio catchment, one of the most impacted by
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