Landslide susceptibility of volcanic landforms in the Río El Estado watershed, Pico de Orizaba volcano, Mexico

The combination of high-quality landslide inventories and geomorphic attributes that can be derived and analyzed by geographic information systems can provide powerful and straightforward input into mapping landscape-wide landslide susceptibility. A methodology for generating landslide susceptibility maps can assist land managers in reducing risk to populations and economic land use from landslide hazards, particularly in areas prone to landslide disasters, such as tropical mountain ranges. Pico de Orizaba is the highest stratovolcano in Mexico, and throughout its geologic history, it has had large landslides triggered by flank collapse as well as small landslides triggered by high seasonal rainfall on terrains covered by poorly consolidated materials. The present work analyzes the distribution of small landslides embedded in volcanic landforms to characterize slope instability. The Río El Estado watershed on the southwestern flank of Pico de Orizaba volcano has been selected as a study area. In the area, landforms are ascertained through aerial photographs, field investigations, and an adaptation of the Landslide Hazard Zonation Protocol of the Washington State Department of Natural Resources, Forest Practices Division in a GIS-based technology. For each landform, a semi-quantitative overall susceptibility rating is derived by using the landslide area rate and the landslide frequency rate. This analysis divides the watershed into seven mass-wasting landforms that are assigned slope stability susceptibility ratings from low to very high. The overall susceptibility rating for this watershed is very high. The technique and its implementation are presented and discussed.