Volcaniclastic debris flow occurrences in the Campania region (southern Italy) and their relation to Holocene - late Pleistocene pyroclastic fall deposits: implications for large scale hazard mapping

Abstract

The Campania Region (Southern Italy) is characterized by the frequent occurrence of volcaniclastic debris flows that produce damage to property and loss of life (more than 170 deaths between 1996 and 1999). Historical investigation allowed the identification of more than 500 events during the last four centuries; in particular, more than half of these occurred in the last 100 years, causing hundreds of deaths. The aim of this paper is to identify debris flow proneness and to quantify hazard. To this end, we compared several elements such as the thickness distribution of pyroclastic fall deposits from the last 18 ka of the Vesuvius and Phlegrean Fields volcanoes, the slopes of relieves, and the historical record of volcaniclastic debris flows from AD 1500 to the present. Results show that flow occurrence is not only a function of the cumulative thickness of past pyroclastic fall deposits but also depends on the age of emplacement. Deposits younger than 10 ka (Holocene eruptions) apparently increase the risk of debris flows, while those older than 10 ka (Late Pleistocene eruptions) seem to play a less prominent role. This is probably in relation to different climatic conditions, and therefore different rates of erosion of pyroclastic falls between the Holocene and the Late Pleistocene. Based on the above considerations, we compiled a large-scale debris flow hazard map of the study area in which five main hazard zones are identified: very low, low, moderate, high and very high.