Hazard map of El Chichón volcano, Chiapas, México: Constraints posed by eruptive history and computer simulations

El Chichón volcano consists of a 2-km wide Somma crater compound cone 0.2 Ma old with peripheral domes with a central crater reactivated several times during the Holocene. The most recent eruption at El Chichón occurred from March 28 to April 4, 1982, resulting in the worst volcanic disaster during historical times in Mexico, killing more than 2000 people and destroying nine towns and small communities. The volcanic hazard map of El Chichón is based on detailed field work that documented twelve eruptions during the last 8000 years, and computer simulations. To validate the results, computer simulations were first performed over pre-1982 topography mimicking the extent of the actual deposits produced and afterwards run over post-1982 topography. These eruptions have produced pyroclastic fall, surge, flow and lahar deposits. Pyroclastic flows have different volumes and Heim coefficients varying from 0.2 (pumice flows), to 0.15 (block-and-ash flows) and 0.10 (ash flows). Simulations using FLOW3D and TITAN2D indicate that pumice flows and block-and-ash flows can fill the moat area and follow main ravines up to distances of ca. 3 km from the crater, with no effect on populations around the volcano. On the other hand, more mobile ash flows related to column-collapse events can reach up to 4 km from the vent, but will always follow the same paths and still not affect surrounding populations. The energy-cone model was used to simulate the outflow of pyroclastic surges based on the 1982 event (H/L = 0.1 and 0.2), and shows that surges may reach some towns around the volcano.Explosive activity also produced Plinian columns higher than 27 km that were dispersed towards the NE by prevailing winds. Future fallout will seriously disturb the lives of more than 70,000 inhabitants of cities and towns located in a radius of 35 km from the volcano. Lahar events in the past originated from unconsolidated pyroclastic deposits with volumes varying from 1 to 4 × 106 m3 for single pulses, to a large one from dam-breakout with a volume of 40 × 106 m3. We used the LAHARZ code to model future events with volumes of 1, 2, and 3 × 106 m3 that will reach as far as 10, 14, and 16 km from the crater, posing some danger to the communities of Nicapa, Volcán, and Ostuacán, even some time after the climax of the eruption.