Inter-eruptive lahars at El Chichón Volcano (Mexico): Susceptibility analysis and numerical modelling

Abstract

El Chichón volcano, located in the southern part of Mexico, is one of the most active Mexican volcanoes. In 1982 it was the scene of the largest Plinian eruption recorded in Mexico during the last century. The volcano is in a climatic region with extreme rainfalls that accumulate more than 3,500 mm of precipitation per year and is frequently affected by hurricanes. The most recent climatic events were caused by Hurricane Eta in 2020 and tropical storm Karl in 2022, in addition to an atypical rainfall event in the same year that accumulated 339.9 mm of rain in 24 hours. During these episodes, hundreds of soil slips originated and transformed into inter-eruptive (e.g., secondary) lahars affecting several communities in the area.

In this work, we present a morpho-hydrological characterization of 33 catchments that drain from the volcano, including their geology and land use changes, to identify the factors promoting mass wasting processes. Moreover, rainfall frequency analysis was performed with data from six weather stations for the period 1987–2017, and precipitation scenarios with return periods of 5, 10, 20 and 80 years were defined. Based on these results, rainfall-runoff simulations using the FLO-2D code allowed us to obtain discharge curves for each catchment, which were used to simulate inter-eruptive lahars from the volcano slopes. We present the first hazard maps for inter-eruptive lahars based on the probability of occurrence and flow magnitude. These maps were subdivided into three scenarios: for 24 hours, 72 hours and an atypical event. The Ostuacán and Xochimilco villages are the most exposed inhabited areas with a total population of 4,000. These maps represent a new contribution to the volcanic hazard assessment of the El Chichón volcano and an essential instrument necessary to contribute to risk management.