Influences of hydrological and hydrogeological conditions on debris flows in peri-vesuvian hillslopes

The paper illustrates some results of research carried out to assess factors triggering debris flows which involve the pyroclastic overburdens covering carbonate mountains around Vesuvius. The aims of the research were to reconstruct a relationship between rainfall and debris flow occurrence and to highlight empirical hydrological thresholds through rainfall pattern analysis. The research was also aimed at investigating hydrogeological features of a pyroclastic cover-carbonate bedrock system to analyse factors inducing temporary hydraulic flow, critical for pyroclastic soil stability. The results of research are the following: i) rainfall pattern highlights empirical hydrological thresholds that differentiate the Lattari and Salerno Mountains from the Sarno Mountains; ii) in some sample areas of the Sarno Mountains close to the trigger zones of the landslides of May 1998 strong variation in hydraulic conductivity has been found in the first few meters below the surface; iii) these permeability variations would seem to justify temporary perched water tables that might affect the stability of the pyroclastic mantle.