Some aspects of the initiation of debris avalanches in the Campania Region: the role of morphological slope discontinuities and the development of failure

In May 1998, a prolonged period of rainfall caused disastrous landslides in the Sarno–Quindici area (Campania, Southern Italy). The landslides initiated as small debris slides, and developed into debris avalanches and debris flows involving the shallow pyroclastic deposits that lie on the steep, vegetated slopes of this area. In view of the potential for such events to occur again in this area, an understanding of the initial failure mechanism is crucial if assessments are to be made of the hazard levels. In this paper, the results of detailed surveys of the morphological characteristics of the source areas are presented. Statistical analyses and parametrical relationships have been performed on key parameters, demonstrating that the initial failures were associated with the presence of morphological discontinuities, such as limestone scarps and road cuts. Notably, the presence of man-made cuts appears to have been responsible for about the 60% of the initial debris slides. Morphometric analysis has shown that the debris avalanches are characterised by a typical triangular shape. Statistical analyses have been used to try to relate the apex angles to relevant geomorphological parameters. Allowing for differences in local morphology the findings show some significant correlation.