A GIS-based method to determine the volume of lahars: Popocatépetl volcano, Mexico

Lahars are flows composed of water and volcanic sediment which are often dangerous for people living near volcanoes. Therefore, a reliable estimation of lahar volume is needed to effectively assess the risk. This paper proposes a new method to calculate the volume of lahar sediments found in channels of volcanic landscapes. The method requires surveys of several cross-sections along a gorge, a Digital Elevation Model of the study area and measurements of the thickness of the lahar deposits. With these data and a Geographical Information System (GIS), the volume is calculated for the erosive section where deposit volume is divided into oblique parallelepipeds and the sedimentary section where deposit volume is divided into polyhedrons. This new method was applied to the 1997 and 2001 lahars that occurred in the channel of a gorge at Popocatépetl volcano, Mexico. The estimated volumes are 1.85 × 105 and 1.6 × 105 m3, respectively, which is about 40% less than those obtained by the traditional method that multiplies lahar flow-path length, sediment width and sediment depth. This observation suggests that the traditional method tends to overestimate volumes.