Resumen

HERNANDEZ AVELINO, Isabel; ACEVES QUESADA, José Fernando  y  LEGORRETA PAULIN, Gabriel. Rockfall inventory, statistical analysis and geomorphological mapping of the Area Nueva Locality in the NE portion of the Sierra de Guadalupe, State of Mexico. Invest. Geog [online]. 2023, n.110, e60677.  Epub 26-Jun-2023. ISSN 2448-7279.  https://doi.org/10.14350/rig.60677.

Among the natural events that have caused great human and economic damage in the world, rockslides occurring on unstable slopes, due to their geological and geomorphological characteristics, together with the triggering factors (earthquakes, torrential rains, anthropogenic processes) that accelerate their fall, stand out. Population growth and the economic position prevailing in many social nuclei, mostly in extreme poverty and in need of housing, is reflected in the occupation of hillside areas, without considering the dangers of rock falls. In areas susceptible to this process, studies have been carried out using various methodologies to determine its causes, the degree of impact on the population living there and the probability of preventing or mitigating it. Since the industrialization during the 1970s in part of the Basin of Mexico and adjacent to the Sierra de Guadalupe, migrants from different states arrived in search of employment, which increased the demand for urban land and, consequently, the territorial occupation of the hillsides of the sierra, where some leaders offered them land at low cost, without considering the risk to which they are exposed by landslides and falling blocks, mainly during the rainy season or when seismic events occur. The formation of the sierra derives from Pleistocene volcanic activity, which has given rise to several volcanoes, domes and spills that present fractures (diaclases) and faults of tectonic origin, with a predominant NW-SE and E-W direction. Prior to intense urbanization the area was used to exploit material banks, which was often done with the help of dynamite for the extraction of materials, which in some areas intensified the fracturing by blasting effects. During the earthquakes that occurred in September 2017, 2 large unstable blocks detached from the dome called "Cerro Gordo", located in the southern portion of the study area. The study area corresponds to the locality of Área Nueva, which is located in the NE portion of the Sierra de Guadalupe, on the southern slope of the La Cantera dome, and which presents an intensely diaclased and fractured escarpment, 450 m long and an average height of 30 m. In this study, an inventory of 114 rockfall deposits was carried out, in which the geographic position, altitude, slope, distance from the escarpment, volume and adherence of the block to the ground surface were obtained for the blocks. With this information and the use of geographic information systems, slope, terrain curvature and geomorphological maps were prepared. The vegetation index (NVDI) was obtained with Sentinel satellite information (analysis of satellite images from 2016 to 2021). In addition to the inventory of rockfall deposits, images of the study area were obtained from a low-altitude drone, whose overflight was at an altitude of 80 m, and the information was subsequently processed to obtain the orthophoto and digital elevation model (DEM). With this information, a statistical analysis was carried out to determine the distribution of the blocks, their size and their potential travel distance. From the results obtained, it was observed that the slope grade significantly influences the potential travel distance of the unstable rock blocks. The distance of travel of the rocks is less when the slopes are greater than 45°, corresponding to the location of the escarpment, and the blocks of smaller volume are those that reach greater distances; however, due to the proximity of human settlements (120 m from the escarpment) and deforestation, the possibility of the blocks breaking off and impacting houses and people increases, causing considerable damage. This risk increases due to the fact that informal constructions continue to be built on the hillside (the "Ricardo Flores Magón" educational complex) and a dirt road cut located between the lower part of the dome and the residential area that connects with other neighborhoods located behind it, which means that there is continuous traffic of inhabitants and their recreational activities. Likewise, deforestation has exposed potentially unstable blocks, which, together with triggering events such as torrential rains and regional and local seismicity, increases the susceptibility to rock falls.

Based on the statistical analysis and the field inventory, it is recommended that the larger unstable blocks be stabilized with anchors, prevent further construction by establishing a safety strip of at least 100 meters from the base of the escarpment, and carry out reforestation programs with forest plantations native to the region.

Raise awareness among the population about the risks of rockfall events in the area and restrict access in order to prevent and mitigate any event that could occur due to this type of process.

Palabras llave : dome; escarpment; slope; deforestation; human settlements.

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