Quantifying lahar damage using numerical modelling

Abstract. Lahars are volcanic flows containing a mixture of fluid and sediment that have caused significant damage to buildings, critical infrastructure and human life. The extent of this damage is controlled by properties of the lahar, location of elements at risk and susceptibility of these elements to the lahar. Here we focus on understanding lahar-induced building damage. Quantification of building damage can be difficult due to the complexity of lahar behaviour (hazard), uncertainty in number and type of buildings exposed to the lahar (exposure) and the uncertain susceptibility of buildings to lahar induced damage (vulnerability). In this paper, we quantify and examine the relative importance of lahar hazard, exposure and vulnerability in determining building damage with reference to a case study in the city of Arequipa, Peru. Numerical modelling is used to investigate lahar properties important in determining the inundation area and forces applied to buildings. Building vulnerability is quantified through the development of critical depth–pressure curves based on the ultimate bending moment of masonry structures. In the case study area, results suggest that building strength plays a minor role in determining overall building losses in comparison to the effects of building exposure and lahar hazard properties such as hydraulic characteristics of the flow.