Estimation of lahar flow velocity on Popocatépetl volcano (Mexico)

During 1997 and 2001 two lahars took place in the Tenenepanco and Huiloac gorges on the northeastern sector of the Popocatépetl volcano in Mexico. These lahars were the result of volcanic activity characterized by a pyroclastic fall and flow. The lahars were triggered by the mass failures produced hours after the eruption. The well-known superelevation technique commonly used in this kind of study was applied to infer the lahar's mean velocity. Estimations show a broad flow velocity range of 1.3–13.8 m/s depending on the following geomorphological parameters: channel depth and slope, peak discharge and distance from the initial source. These results were compared with lahar velocities from Mount St Helens (1980) and Nevado del Ruiz (1985), which were obtained by the same superelevation technique. According to the data, the lahars from Nevado del Ruiz and Popocatépetl were triggered by similar conditions, while at Mount St Helens they were the result of the conversion of a pyroclastic surge cloud. Actually, the Mount St Helens lahars were almost twice as fast as the ones at Nevado del Ruiz and Popocatépetl. This observation shows the importance of the lahars' genesis in that the pyroclastic surge clouds produce faster lahars than do pyroclastic falls. Such results should be taken into account in lahar risk assessment studies for communities located near active volcanoes.