Mass movement processes at the Motozintla Basin, Chiapas, Southern Mexico

Prediction of prone areas for mass movement processes (MMP) is one of the major challenges in mountainous areas. This is the case of the Motozintla basin that is located along the Motagua-Polochic fault system in the Chiapas State southeastern Mexico. The area is dominated by Permian to Tertiary rocks extremely affected by faults, weathering and intense erosion. Motozintla has been seriously disrupted by two hydrometeorological phenomena in 1998 and 2005. In this paper, geological and structural mapping (1:30 000), photointerpretation and GIS techniques were applied to determine the hazard areas that may go off by mass movement processes driven by gravity in the basin. The inventory shows 88 mapable mass movement processes ocurred during the past 25 ky represented by debris avalanches, rock falls, slides and debris flows. Debris flows are the most dangerous phenomena that may directly impact the city of Motozintla posing at risk 23,755 people. Future mass movement processes may happen mainly in the NW part of the basin where highly altered rocks of the Chiapas massif and Todos Santos Formation are exposed.