Abstract

GARCIA REYES, Sandra; LEGORRETA PAULIN, Gabriel  and  ACEVES QUESADA, Fernando. Geomorphological Susceptibility to Gravitational Processes in Secondary Streams in Southern La Ciénaga watershed, Nevado de Toluca volcano. Invest. Geog [online]. 2018, n.96. ISSN 2448-7279.  https://doi.org/10.14350/rig.59613.

Landslides are geomorphological processes that occur in the earth’s relief all the time and are caused by natural and man-made factors. Such phenomena have unleashed a series of major economic and social disasters. To mitigate these problems, it is necessary to stablish the causes, the spatial patterns, and the factors that produce this gravitational phenomenon.

In Mexico, a large number of landslides have occurred in recent years, many of them in the Trans-Mexican Volcanic Belt. This gravitational phenomenon has been addressed through the compilation of historical or multitemporal landslide inventories and by using the integration of diverse heuristic, statistical, and deterministic methods to produce landslide susceptibility maps. However, there are few geomorphological studies that relate the area and the frequency with which landslides affect the susceptibility of landforms.

The present research is based on studies of the stream system of the Río La Cienega watershed on the estern flank of Nevado de Toluca volcano, Mexico. The climatic, topographic, and geological conditions predispose the study area to episodic landslides and debris flows that creates a hazardous situation for people living along the stream system. For example, in 1940 rainfalls triggered landslides on the up-stream of La Cienega watershed. The landslide sediments increased the destructive power of a debris flow that caused loss of life and property at the town of Santa Cruz belonging to the municipality of Tenango del Valle, State of Mexico. As a result of this event the inhabitants rebuilt the village that is currently called Santa Cruz Pueblo Nuevo, however this relocation was made without an adequate planning in the lower part of the watershed on an alluvial fan, which is prone to new and future landslides and debris flows. Despite of its importance, there is a lack of landslide inventories that aid the assessment of landslide susceptibility in the watershed. Our work is focus in two secondary rives located in the southern portion of the La Ciénega watershed. These secondary rivers are referred as La Cieneguilla 1 (ASC1) and La Cieneguilla 2 (ASC2). In both tributaries, a detailed landslide inventory and a geomorphological map were carry out in order to determine the landslide susceptibility by landforms. The methodology encompasses four main stages of analysis to assess landslide susceptibility. During the first stage, background information was collected to provide a generalized characterization of landslides processes within the watershed. Background information includes geology, land use, climate and hydrology, preexisting landslide maps and reports, etc. In the second stage, a single historic landslide inventory map was created with sets of satellite images from different time and fieldwork. One hundred seventy-nine landslides were mapped and documented in the GIS. During the third stage a geomorphological map was obtained by interpretation of aerial photographs, a digital elevation model (MDE), geology, and morphometric maps. The geomorphological map allowed to highlight the relevant landforms in the watershed. The fourth stage stablish the landslide susceptibility per landform by using the landslide frequency and the landslide area. This method follows and adapt the Washington State, Department of Natural Resources Landslide Hazard Protocol.

The results show that debris slides are the most frequent processes along the two secondary rivers and have the potential to damages the town of Santa Cruz Pueblo Nuevo and other rural areas. Along the two secondary rivers, three landforms out of fourteen have the highest landslide susceptibility. In these landforms, factors such as steep slopes, geological faults, and slope morphology influence the abundance and distribution of landslides.

Keywords : Landslides; inventory; frequency; susceptibility; Nevado de Toluca volcano.

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