A GIS-based methodology for hazard mapping of small volume pyroclastic density currents

We present here a methodology implemented within a geographical information system (GIS) for hazard mapping of small volume pyroclastic density currents (PDCs). This technique is implemented as a set of macros written in Visual Basic for Applications (VBA) that run within GIS-software (i.e. ArcGIS). Based on the energy line concept, we calibrated an equation that relates the volume (V) and the mobility (Delta H/L) of single PDCs using data from Soufriere Hills volcano (Montserrat) and Arenal volcano (Costa Rica). Maximum potential run-outs can be predicted with an associated uncertainty of about 30%. Also based on the energy line concept and with data from Soufriere Hills volcano and Mt. St. Helens (USA), we were able to calibrate an equation that predicts the flow velocity as a function of the vertical distance between the energy line and the ground surface (Delta h). Velocities derived in this way have an associated uncertainty of 3 m s(-1). We wrote code to implement these equations and allow the automatic mapping of run-out and velocity with the inputs being (i) the height and location of the vent (ii) the flow volume and (iii) a digital elevation model (DEM) of the volcano. Dynamic pressure can also be estimated and mapped by incorporating the density of the pyroclastic density current (PDC). This computer application allows the incorporation of uncertainties in the location of the vent and of statistical uncertainties expressed by the 95% confidence limits of the regression model. We were able to verify predictions by the proposed methodology with data from Unzen volcano (Japan) and Mayon volcano (The Philippines). The consistencies observed highlight the applicability of this approach for hazard mitigation and real-time emergency management.