Volcaniclastic debris flows in the Clanio Valley (Campania, Italy): insights for the assessment of hazard potential M.T. Pareschi a, * , R. Santacroce b , R. Sulpizio b , G. Zanchetta b a CNR Centro di Studio per la Geologia Strutturale e Dinamica dell’Appennino, Via S. Maria 53, 56126 Pisa, Italy b Dipartimento di Scienze della Terra, Universita ` di Pisa, Via S. Maria 53, 56126 Pisa, Italy Received 2 January 2001; received in revised form 24 July 2001; accepted 27 July 2001 Abstract The rugged and steep slopes of the Clanio Valley (Campania, Southern Italy), mantled by volcaniclastic deposits from explosive eruptions of Somma-Vesuvius and Phlegraean Fields volcanoes, have a great potential for generating volcaniclastic debris flows. During the well-known meteorological event of May 5 – 6, 1998, which triggered tens of debris flows causing enormous damage and casualties in the area of Sarno –Quindici – Siano– Bracigliano (SQSB), the Clanio Valley was also affected by these hazardous phenomena. Debris flows were triggered by the failure of the volcaniclastic cover of the carbonate relief in the form of soil slips, mainly on the sides of steep valleys (slope between 26° and 45°). A map of the hazard potential was created on the basis of both field and computer-assisted morphometric data. Three classes, characterised by a high, medium and low hazard potential, were distinguished. Within the higher class, a better and more detailed zonation was obtained by studying the shape of the disrupted and undisrupted basins during the May 5 – 6, 1998 event in the nearby Sarno – Quindici – Siano – Bracigliano area. This type of morphometric analysis can be applied rapidly by using a digital elevation model (DEM), which allows a rapid investigation of large-scale areas. Such an approach can be useful in areas characterised by similar geological and geomorphological settings. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Volcanoclastic debris flow; Hazard zonation; Somma-Vesuvius; Phlegraean fields; Southern Italy 1. Introduction The hazard caused by volcaniclastic debris flows is a permanent feature in circumvolcanic areas affected by recurrent pyroclastic deposition (Pareschi et al., 2000a). At any time, during and after an eruption, intense rainfall can trigger debris flows in steep areas. Although volcaniclastic debris flows can have various causes (Rodolfo and Arguden, 1991; Takahashi, 1991; Pierson, 1995), soil slips predominate for a long time after eruptions, especially in areas where soil develop- ment is rapid enough to stabilize the loose volcanic products (e.g. Ellen and Fleming, 1987; Iverson et al., 1997; Pareschi et al., 2000a). The rugged and steep slopes downwind of the Somma-Vesuvius and Phlegraean Fields volcanoes, in southern Campania (Italy), are suitable areas for the formation of volcaniclastic debris flows. This has been shown tragically in the last few years by the disasters of Palma Campania (1983), Bagni di Poz- zano (1997), Sarno (1998) and Cervinara (1999), as well as by several other historical events (Migale and 0169-555X/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII:S0169-555X(01)00134-9 * Corresponding author. Fax: +39-50-500932. E-mail address: pareschi@dst.unipi.it (M.T. Pareschi). www.elsevier.com/locate/geomorph Geomorphology 43 (2002) 219 – 231