OBSERVATIONS OF POTENTIAL MASS MOVEMENTS IN THE RURAL AREAS OF OAXACA, MEXICO

Comprehensive landslide risk assessments involve detailed analyses of topography, geomorphology, precipitation/drainage, seismicity and land use. Rural areas in Oaxaca, Mexico, are used for agriculture and are located on unstable slopes, according to risk maps currently available from Mexico’s National Center for Prevention of Disasters (CENAPRED). Entire towns are built on steep slopes thus increasing the risk of slope failure and endangering the local communities. Landsat and SPOT imagery of the Sierra Norte, Oaxaca, were analyzed in ArcGIS to understand changes of the land surface and identify potential landslides via geomorphological characteristics.

Google Earth Pro was used for 3D visualization, to measure landslide surface area for those sites that were not in the coverage of the SPOT imagery. The historical tool aided in verifying the presence of a mass movement by comparing older imagery with newer. In order to fully tell if the area observed had any potential for failure, areas that appeared patchy, lobe-like, or had drastic changes in vegetation or noticeable escarpments were catalogued. Digital Elevation Models (DEMs) and slope maps were created in ArcMap to create a slope analysis. The slope map was used to understand whether the points identified in Google Earth Pro were located in an area with a high percent slope.

Agricultural fields have been spreading more to the west as noted in the SPOT imagery taken in 2015, compared to older imagery housed in Google Earth Pro. Some effects from this spreading could be deforestation, thus increasing the risk for slope failure. Nineteen potential sites for failure have been identified; 5 of the sites were identified in the SPOT imagery. These sites have been categorized as flow, slide, or creep. Sites that were classified as flows are based on the presence of long narrow tongues. Slides were determined mostly by areas with a head scarp, and the preservation of relict structures. Creep areas usually displayed lobes instead of an obvious scarp. Future work will continue to analyze DEMs, satellite imagery and aerial photographs in ArcGIS to classify the different types of landslides in the study area. The goal of this project will be to use the classification along with precipitation and seismicity maps to help refine the potential for landslide risk.