HYDRAULIC BEHAVIOUR AND SIMULATION OF VOLCANIC DEBRIS FLOWS IN POPOCATEPETL VOLCANO, MEXICO

Debris flows are composed of more than 40% water, with the rest made up of debris. Lahars can be debris and hyperconcentrated flows that rapidly descend volcanoes' slopes jeopardizing inhabitants living close to volcanic areas. Popocatépetl volcano has 5,450 m ASL and is located in Central Mexico, where lahars frequently flow downstream through two gorges named Tenenepanco and Huiloac. The first one has its starting point below a glacier located on the north face of the volcanic edifice, just above 4,800 m ASL. Tenenepanco gorge joins Huiloac at ~3,700 m ASL, which has it mouth at 2,600 m ASL after crossing the village of Santiago Xalitzintla (~2,500 inhabitants). The most recent lahars occurring at Popocatépetl volcano took place on the 1st July 1997 and the 22nd January 2001; both were generated as a consequence of the eruptive activity initiated in the volcano in 1994 that continues to this day. The lahar of 1997 crossed the village of Santiago Xalitzintla flooding some houses and the lahar of 2001 stopped around 2 km before reaching the village. Since there is a constant risk of lahars flooding the village of Santiago Xalitzintla, this work analyzes: 1- the hydraulic and sedimentological behaviour of the lahars of 1997 and 2001 and 2- the lahar simulation of hypothetical extreme volume lahars in the Popocatépetl using the program LAHARZ. To achieve the first goal, field work was carried out to collect data to calculate the different hydraulic and sedimentological parameters of these two lahars along their path. The flooded areas mapped for 1997 and 2001 lahars as well as their calculated volume were used to calibrate LAHARZ simulations in the Popocatépetl volcano. To run these simulations, two GIS methods were developed and applied to the study area. The first method was elaborated to update the channel cross-sections in a Digital Elevation Model by using different profiles surveyed during field work; and was applied to the Tenenapanco and Huiloac channels. The second method was developed to calculate accurately the volume of the sediment deposited by a lahar after it comes to rest to facilitate the measuring of different lahar sediment thicknesses along its path, taking into account the sedimentological behaviour of the flow. This was used to calculate the volume of the lahars which occurred in 1997 and 2001.