Debris slides-rapid earth flows in the carbonate massifs of the Campania region (Southern Italy): Morphological and morphometric data for evaluating triggering susceptibility

摘要

This paper examines the morphological and morphometric properties of debris slides-rapid earth flows which have occurred in pyroclastic deposits of the Campania region over the last few centuries. The slopes bordering the main carbonate massif of western Campania are covered by several metres of pyroclastic deposits from the Somma-Vesuvio volcano that, due to the steepness of the slopes, are easily eroded by surface waters and periodic debris slides-rapid earth flows. These flows are sudden and unpredictable, and have caused both damage to the environment and loss of life over the last few decades. After consulting scientific papers and historical documents, the areas most recently affected by debris slides-rapid earth flows were analysed through aerial photographs and a geological survey. An inventory of 172 landslides was produced, and landslides were mapped at a scale of 1:2000 for further geomorphological and morphometric analysis. Morphological analysis was primarily concerned with predisposing factors; it confirmed that 86% of the slope failure crowns developed in response to man-made cuts and tracks (44%), or due to the presence of cliffs (42%). Two different kinds of slopes are affected by debris slides-rapid earth flows: slopes lacking drainage basins and slopes cut by one or several drainage basins. Typical triangular-shaped earth flows with a landslide mass located at the foot of the slope (unchannelled debris slides-rapid earth flows) were found along the former slopes. In contrast, channelled debris slides-rapid earth flows formed along the latter slopes. These originated in the drainage divide area, developed along the main water segment and invaded the alluvial plain far from the foot of the slope. An intermediate group of flows started as triangular shaped and then became channelled. Morphometric analysis also investigated the parameters most commonly found in the literature (slope angle of the crown and sliding zone, crown altitude, areal extent of the landslide), together with other parameters (apical angle of the crown zone and landslide body, slope relief energy and potential zone of triggering). This analysis identified critical values for the steepness of crown zones and for the steepness of the sliding zone. Critical values of the apical angle of the crown zone for mixed and unchannelled landslides were also established. Correlations among some of the investigated parameters were investigated; in particular, the relationships between slope relief energy and areal extent of landslides or the height of the landslide crown zone. All the factors and parameters analysed in this paper can be used to identify areas which need to be stabilized or monitored, and could be important for planning defensive measures of debris slides-rapid earth flows.