Resumo

HINOJOSA-CORONA, Alejandro; RODRIGUEZ-MORENO, Víctor Manuel; MUNGUIA-OROZCO, Luis  e  MEILLON-MENCHACA, Octavio. The landslide of November 2007 and generation of a natural dam in the Grijalva River, Chiapas, Mexico. Bol. Soc. Geol. Mex [online]. 2011, vol.63, n.1, pp.15-38. ISSN 1405-3322.

On the night of November 4^th 2007 a landslide of 48 million cubic meters of rocks and mud with an extension of 80 ha produced a natural barrier to the Grijalva River, one of the largest in Mexico, obstructing its natural fow between the Peñitas (downstream) and Malpaso (upstream) dams and forming a natural barricade 80 m high, 800 m long and 300 m wide. The rural town of San Juan de Grijalva, located on the shoreline of the river, was affected by the moving block and the sudden fooding of a wave generated by the landslide. A death toll of 25 was reported. Assisted with remote sensing and geographic information systems tools, we present the landslide and the Grijalva River watershed in the context of the natural dam and abnormal precipitation during late October and early November 2007. Through high resolution satellite imagery and digital elevation models, a pre- and post-landslide perspective is presented. An airborne Lidar high resolution elevation model was used to analyze the landslide once it occurred. Synthetic stereo pairs were constructed, one previous to the landslide to photo interpret lineaments and one after it to visualize the phenomenon. Plots of transects across pre- and post -landslide elevation models illustrate the magnitude of the landslide. From the Lidar elevation model, a general landslide surface plane was calculated with a slope of 28 % and 239 degrees in azimuth. The different factors that could have triggered the landslide are analyzed, without finding an outstanding one. We consider that the cause was a sum of factors with a delayed response of a few days.

Palavras-chave : Grijalva River; landslides; remote sensing; Lidar; digital elevation model; natural dam formation.

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