Assessing Landslide Frequency for Landform Hazard Zoning Purposes

Abstract

This work provides an overview of the on-going research project (Grant PAPIIT, no. IB100412-RR180412 and IPL project #170) from the Institute of Geography at the National Autonomous University of Mexico (UNAM). The project seeks to conduct a multi-temporal landslide inventory, analyze the distribution of landslides, and characterize landforms that are prone to slope instability by using Geographic Information Systems (GIS). The study area is the Rio Chiquito-Barranca del Muerto watershed that covers 111 km2 and lies on the south-western flank of Pico de Orizaba volcano. The watershed was studied using aerial photographs, fieldwork, and adaptation of the Landslide Hazard Zonation Protocol of the Washington State Department of Natural Resources, USA. A total of 571 gravitational features were recognized, of six types: shallow landslides, debris-avalanche, deep-seated landslides, debris flows, earthflows, and rock falls. This analysis divided the watershed into 12 mass-wasting landforms on which gravitational processes occur: inner gorges, headwalls, active scarps of deep-seated landslides, meanders, plains, three types of hillslopes classified by their gradient (low, moderate, and high), rockfalls, non-rule-identified inner gorges, non-rule-identified headwalls, and non-rule-identified converging hillslopes. For each landform the landslide area rate and the landslide frequency rate were calculated, as well as the overall hazard rating. The slope-stability hazard rating has a range that goes from low to very high. The overall hazard rating for this watershed was very high.