Numerical modeling and hazard implications of landslides at the Ardillas Volcanic Dome (Tacaná Volcanic Complex, Mexico-Guatemala)

The upper flanks of stratovolcanoes usually exhibit steep slopes affected by fumarolic or hydrothermal activity. These conditions commonly promote rock instability, triggering rock avalanches and landslides. Quiescent and active stratovolcanoes transected by fractures and faults are further susceptible to these phenomenon, especially when they are located in tropical regions, where heavy rainfall regimes tend to saturate the volcanic material and promotes landslides. One example of such volcanoes is the Tacaná Volcanic Complex located at the Mexico-Guatemala border. It consists of three NE-SW aligned volcanoes (Chichuj, Tacaná, and San Antonio) and the Ardillas Dome. Just recently, the eastern portions of Ardillas Dome and San Antonio volcano have been affected by rockfalls and landslides toward the southern flank of the Complex, particularly to the Maxaum ravine. Field surveys showed tension fractures, landslide scars, fumaroles and volcanic vents along an important NE-SW fissure that has been growing between these two volcanic structures. To assess a future landslide within this zone, we delineate an area prone to collapse, according to the structural and morphometric analysis. We simulate a set of five gravitational flows of different volumes (1 × 105 to 2.5 × 107 m3) with the numerical code Titan2D varying the source area of the landslides. The simulated landslides showed that independently of the volume involved or source point of the landslide, it will be channeled within the Maxaum ravine and travel a maximum distance of up to 7 km from the source. The simulated flows moved at maximum velocities of ~ 41 m/s and were dispersed over a surface area of ~ 17 km2 with variable thicknesses (0.5–7 m at the affected villages). The most voluminous landslides (2.5 × 107 m3) will impact at least eight villages inhabited by ~ 2000 people on the southern flanks of the Complex. By analyzing the potential building damage caused by the largest simulated landslide (intensity index, IDF), two localities would have major structural damages in their dwellings and two would be completely destroyed; meanwhile, another three villages would suffer minor structural damages and one would experience minor sedimentation. Although the outcomes described here represent the first evaluation of small-volume landslide hazards at the Complex, specifically at the Ardillas Dome, our maps are useful tools for the preparedness for the Civil Protection authorities and the population at risk. Thus, a detailed landslide hazard assessment is needed, taking into account the present state of the Tacaná Volcanic Complex as well as the geologic and climatologic setting of the volcano, and a full stability analysis.