Numerical simulation of block-and-ash flows for different eruptive scenarios of the Tacaná Volcanic Complex, México-Guatemala

Abstract

Abstract The Tacana Volcanic Complex (TVC), shared by Mexico and Guatemala, is considered an active volcano that resumed phreatic explosions in 1949 and 1986. The TVC has recorded at least eight eruptions emplacing block-and-ash flows (BAFs) around the volcanic edifice during the past 42,000\u202fyears. The largest event generated the Mixcun deposit some 1950\u202fyr\u202fB.P. from San Antonio Volcano, the youngest structure of the complex. Based on the eight mapped BAF deposits of the complex, we perform numerical simulations with the TITAN2d code to recreate the distribution and extent of these deposits. The results were used to prepare the zonation of the TVC based on the surface bed friction angles, which are related to the different morphologies of the volcano. From this zonation and the features of the past BAF deposits, we define three new eruptive impact scenarios (low, medium and high), to perform a hazard assessment of this phenomenon but considering the present morphology of the complex of the four eruptive centers. Next, we ranged the input parameters for each case scenario to analyze the dispersal, thickness and maximum runout of simulated flows. From the numerical simulations, we found that the most influential parameter in the model outputs is the basal friction angle, which varied from 23° to 12°. Then, we merged the eruptive scenarios simulated to construct new hazard maps for the different mass volumes simulated for each scenario. These maps clearly evidenced that the Mexican territory would be seriously affected in case of a renewed explosive activity of the TVC. In fact, even the partial collapse of any of the TVC domes would produce BAFs capable to flow over ~70 communities affecting ca. 20,000 inhabitants, as well as promote the generation of syn-and-post eruptive lahars if they flow into the main rivers that drain the volcano. Therefore, these maps are a great advance to evaluate the destructive potential of the TVC and must serve as the basis for the construction of a new risk map by the local authorities to update the operative and evacuation plans of the region. These actions would help to the >350,000 inhabitants living in a 35\u202fkm radius from the volcano s summit to be aware of the perils posed by the volcano, and how to act and evacuate in case of a volcanic crisis.