Redalyc.Susceptibility to Shallow Landslides of Soil in the Municipality
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Investigaciones Geográficas (Mx) ISSN: 0188-4611 [email protected] Instituto de Geografía México Flores, Patricia; Alcántara Ayala, Irasema Susceptibility to shallow landslides of soil in the municipality of Temoaya, Mexico: multicriteria analysis Investigaciones Geográficas (Mx), núm. 77, 2012, pp. 31-47 Instituto de Geografía Distrito Federal, México Available in: http://www.redalyc.org/articulo.oa?id=56923353004 How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative Investigaciones Geográficas, Boletín del Instituto de Geografía,UNAM ISSN 0188-4611, Núm. 77, 2012, pp. 31-47 Susceptibility to shallow landslides of soil in the municipality of Temoaya, Mexico: multicriteria analysis1 Received: 10 December 2010. Final version accepted: 28 September 2011. Patricia Flores* Irasema Alcántara Ayala** Abstract. Owing to the mountainous character of the Mexi- these are permeable materials they favour infiltration; if the can terrain, as well as the ecological effects of changes in land subjacent material is impermeable or of low permeability, use, particularly in recent decades, and the occurrence of water accumulates on the sub-horizontal lithological contact severe and frequent hydro-meteorological phenomena, the and transforms into a flow that leads to the instability of instability of slopes dislodged by precipitation constitutes the overlying material. a major hazard in various regions of the country, among A map of susceptibility to SSTLs was generated by means them the municipality of Temoaya in the State of Mexico. of a multicriteria analysis. According to the map produ- In this municipality, where the mountainous relief ced, 15% of the municipality is very highly susceptible to formed by poorly consolidated and faulting volcaniclastic landslides, 35% is highly susceptible, 30% shows medium deposits favours instability, there are 33 active processes of susceptibility, and the remaining 20% has low or very mass movement, of which thirty –the most important– are low susceptibility. shallow soil translational landslides (SSTL), one is a debris slide and two are rock falls. The occurrence of SSTLs is con- Key words: Shallow soil translational landslides, multicri- trolled by the character of the volcaniclastic deposits, speci- teria analysis, susceptibility, Temoaya. fically pyroclastic flows of blocks, ash and pumice; because Susceptibilidad a deslizamientos superficiales de suelo en el Municipio de Temoaya, México: aplicación del análisis multicriterio Resumen. Debido al carácter montañoso del espacio geo- favorece la inestabilidad, existen 33 procesos de remoción gráfico mexicano, así como del impacto ecológico generado en masa activos, de los cuales treinta -los más importantes-, por los cambios de uso de suelo, efectuados particularmente son deslizamientos de suelo superficiales de tipo traslacional en las últimas décadas, y de la ocurrencia de fenómenos (DSST), un deslizamiento de derrubios y dos caídas de rocas. hidrometeorológicos de gran intensidad o frecuencia, la La ocurrencia de los DSST está controlada por el carácter inestabilidad de laderas desencadenada por precipitación de los depósitos vulcanoclásticos, específicamente flujos constituye uno de los peligros de mayor impacto en diver- piroclásticos de bloques, cenizas y pómez, los cuales al ser sas regiones del país, entre ellas el municipio de Temoaya, materiales permeables favorecen la infiltración, por lo que si Estado de México. el material subyacente es impermeable o de menor permeabi- En este municipio, donde el relieve montañoso formado lidad, se presenta una acumulación de agua sobre el contacto por depósitos vulcanoclásticos poco consolidados y afallados 1 Traduction of Dr. Ann Grant. * Posgrado en Ciencias de la Tierra, Universidad Nacional Autónoma de México. E-mail: [email protected] ** Departamento de Geografía Física, Instituto de Geografía, Universidad Nacional Autónoma de México, Circuito de la Investigación Científica, 04510, Coyoacán, México, D.F. E-mail: [email protected] Patricia Flores and Irasema Alcántara Ayala litológico subhorizontal que se transforma en un flujo que de alta susceptibilidad ocupa el 35% del área en cuestión. conduce a la inestabilidad del material sobreyacente. El nivel de susceptibilidad medio se concentra en el 30% En este trabajo se presenta la aplicación del Método del territorio, y en el restante 20% de la zona de interés, la de Análisis Multicriterio para la generación de un mapa de susceptibilidad a deslizamientos es baja y muy baja. susceptibilidad a deslizamientos de suelo superficiales de tipo traslacional para dicha zona. De acuerdo con el mapa Palabras clave: Deslizamientos de suelo superficiales de tipo elaborado, el 15% del territorio municipal presenta muy traslacional, análisis multicriterio, susceptibilidad, Temoaya. alta susceptibilidad a deslizamientos, mientras que la zona INTRODUCTION Viejo community, damaging 20 cars and killing 10 people (La Jornada, 6 February 2010). Slope instability Temoaya municipality in the State of México, Hillslopes can be subject to an instability known in the foothills of the Sierra de Las Cruces (Figure as mass movement processes or gravitational 1), is under considerable anthropogenic pressure processes (Alcántara, 2000a). According to the owing to deforestation, mining, crop and livestock EPOCH (1993) classification, these include falls, production, logging on the slopes to build hou- topples, slides, lateral expansions, flows and com- ses, and roads. This has led to landslides and the plex movements. Mass movement processes can be potential for damage to dwellings, roads and agri- natural or anthropogenic. The natural events are cultural lands. The present study assesses the threat highly important in the continuous sculpting of of soil slides in this municipality with the aim of the mountainous relief, since they form part of the producing information that may contribute to the natural cycle of evolution of the relief of the land appropriate management of the region and to mass (Lugo et al., 2001); they result from the direct decision making in relation to disaster prevention. influence of gravity in combination with internal Specifically, the present article aims to analyse or external factors, and of triggering mechanisms the zones susceptible to shallow soil translational such as tremors, precipitation, volcanic activity landslides (SSTLs) in Temoaya municipality, the and explosions (Crozier, 1986). Mass movement State of México, by multicriteria analysis of inte- processes can also be the result of anthropogenic rrelationships between variables such as gradient, activities that generate a disequilibrium in the hills- geology, geomorphological units, land use, roads lopes through terracing, deforestation, agriculture and morphometry. (Alcántara, 2002:47), or there may even be an interaction of natural and anthropogenic factors. Assessment of mass movement processes According to Alcántara (2010), during the Where many factors are important in the oc- period 1900-2000 in Mexico and in Central Ame- currence of a hazard, analysis involves complex rica, disasters caused by mass movement processes investigations (Van Westen, 1994), and can be affected 10 million people and 53,771 died. In expressed through cartography, i.e. production Mexico, rains caused by tropical depression No.11 of maps of various kinds of zoning, such as those in 1999 caused gravitational processes in the Sierra of susceptible areas, which can serve as a basis for Norte de Puebla that killed 250 people; this was mitigation, planning and decision making. considered to be the worst disaster of the 1990s in The methods proposed for assessing mass move- Mexico (Bitrán, 2000, Lugo et al, 2005:22). ment processes form two main groups: qualitative In the State of México in 1912 a quake of 6.9 on (direct) and quantitative (indirect), (Soeters and the Richter scale caused a rockfall in the Acambay Van Westen, 1996). The qualitative methods invol- municipality, and several dwellings were affected ve direct assessment of the mass movements, on the and there were some 700 deaths (Gobierno del Es- basis of specialist knowledge; they include inventory tado de México, 1998). In February 2010, intense of slope processes and heuristic analysis (geomorpholo- rains caused mass movement processes in a section gical analysis and qualitative combination of maps). of the Toluca-Temascaltepec highway in the Mesón The quantitative methods consist of mapping a 32 ][ Investigaciones Geográficas, Boletín 77, 2012 Susceptibility to shallow landslides of soil in the municipality of Temoaya, Mexico: multicriteria analysis large number of parameters that are subsequently occupy the principal row (Voogd, 1983, in Barredo analysed statistically, for example by bivariate and 1996). This matrix can have names such as decision multivariate statistical analysis, which are based matrix, effectivity matrix, project-effect matrix or on the relationship of natural determinant factors evaluation matrix. Subsequently, values designated to the distribution of existing landslides (Clerici, criteria scores are assigned within the matrix. They 2002:48), and also their relationship to the density represent the value or level of desirability that each of landslides, through the superposition of layers.