Juan Grijalva

A large block slide occurred on the south face of the Cerro La Pera, in the locality of Juan Grijalva (JG), municipality of Ostuacan, northwest Chiapas (Mexico). The JG landslide (1.11 km2 / 50 Mm3) created a dam over 80 m high and 1,170 m wide across the Grijalva River (the second largest river in Mexico), backing up the water and forming a 49 km2 lake. Landslide-generated tsunamis up to 15 m high destroyed the village of JG and killed 16 people. The newly formed lake flooded 21 villages located upstream and around 3,600 people to be evacuated with incalculable economic losses. Further, the probable dam-landslide collapse put at risk the Peñitas dam and the city of Villa Hermosa (Tabasco) located downstream 14 km and 120 km, respectively. It was perhaps the most catastrophic landslide in the history of Mexico. The probable trigger of the landslide was cumulative precipitation of about 67% of the average annual rainfall over the preceding 30 days, and a water-level drawdown at the Grijalva River generated by the release of water from the Peñitas dam. After works carried out by the Comisión Federal de Electricidad to join the river and stabilize the slope, the landslide is motionless.