EXTREME EVENTS IN TROPICAL AREAS – HURRICANE MANUEL AND LA PINTADA LANDSLIDE DISASTERS

Extreme events in regions of humid-warm tropical climate are repeatedly causing loss of life and economic devastation. Deadly landslides are commonly triggered by extreme storms. Many of them originate on mountain slopes along river systems in areas often populated, increasing the risk to human settlements and activities.

Frequently hit by hurricanes and tropical cyclones the mountainous areas of Guerrero in southern Mexico are particularly prone to landslide hazard. On 16 September 2013 a huge landslide caused 71 fatalities and destroyed a large part of the La Pintada village. The landslide initiated after extreme rainfall caused by Hurricane Manuel. We performed a post-landslide field survey, applied remote sensing techniques using 1 m resolution LIDAR DEM and images, digital models derived from Structure from Motion (SfM), satellite images, orthophotomaps, eyewitness accounts, geotechnical laboratory tests of slope material, and slope stability analysis to examine physical characteristics and processes that influenced the failure of La Pintada landslide.

Our results indicate that a 4-day long rainfall (> 500 mm, i.e. more than a monthly average) related to the hurricane Manuel landfall that hit western Mexico on September 2013, and produced oversaturation of soil, was the direct factor that initiated the La Pintada landslide. The effect of rainfall was amplified by the lack of high and dense vegetation on a 250 m high slope. It is likely that human activity contributed to the decrease of slope stability by deforestation and by cutting the slope to build houses at the toe of the slope. Seismic activity, even if did not contribute directly to the initiation of the La Pintada landslide, might have promoted the decrease in slope stability.

We hypothesized that climate change has contributed to the short recurrence period of extreme meteorological events that triggers landslides in this tropical area. Furthermore, the location of the Guerrero mountains in an active forearc, together with deforestation of slopes and increasing human population makes this area of Guerrero highly vulnerable to landslide hazard.