Rapid terrain-based mapping of some volcaniclastic flow hazard using Gis-based automated methods: a case study from southern Campania, Italy

Abstract

Destructive volcaniclastic flows are among the most recurrent and dangerous natural phenomena in volcanic areas. They can originate not only during or shortly after an eruption (syn-eruptive) but also during a period of volcanic quiescence (inter-eruptive), when heavy and/or persistent rains remobilize loose pyroclastic deposits. The area in Italy most prone to such flows is that of the Apennine Mountains bordering the southern Campania Plain. These steep slopes are covered by pyroclastic material of variable thickness (a few cm to several m) derived from the explosive activity of the Somma-Vesuvius and Campi Flegrei volcanoes a few tens of kilometers to the west. The largest and most recent devastating event occurred on May 5, 1998, causing the death of more than 150 people and considerable damage to villages at the foot of the Apennine Mountains. This tragic event was only the most recent of a number of volcaniclastic flows affecting the area in both historical and prehistoric times. Historical accounts report that more than 500 events have occurred in the last five centuries and that more than half of these occurred in the last 100 years, causing hundreds of deaths. In order to improve volcaniclastic flow hazard zonation and risk mitigation in the study area, we produced a zonation map that identifies the drainage basins potentially prone to disruption. This map was obtained by combining morphological characteristics (concavity and basin shape factor) and the mean slope distribution of drainage basins derived from a digital elevation model with a 10-m resolution. These parameters allowed for the classification of 1,069 drainage basins, which have been grouped into four different classes of proneness to disruption: low, moderate, high and very high. The map compiled in a GIS environment, as well as the linked database, can be rapidly queried.