UNDERSTANDING LANDSLIDE-RAINFALL RELATIONSHIPS IN MAN-MODIFIED ENVIROMENTS: A CASE HISTORY FROM CARAMANICO TERME (ITALY)

J. Wasowski (CNR CERIST Bari, via Orabona 4, 70125 Bari, Italy)

After examining the rainfall triggered landslides in the municipal territory of Caramanico Terme (south-central Apennines), this paper draws attention to some problems regarding the application of general threshold rainfalls to man-modified slopes in mountainous environments. The expansion of the town of Caramanico Terme in this century led to the urbanization of marginally stable river valley slopes and to the construction of new transportation routs in the surrounding mountainous areas. The town's development coincided with the apparent acceleration of landslide processes and more frequent occurrence of damaging mass movements. The main landslide events which have taken place in the last few years in the Caramanico area represent partial remobilizations of older slide bodies and enlargements of long-lived slope failures. All of these recent mass movements occurred on man-modified slopes and were triggered by heavy and/or prolonged precipitations. In the same period, on the contrary, no important landslides on natural slope were reported in the Caramanico area. Furthermore, the examination of the Caramanico Terme precipitation record (1922-Present) revealed the presence in the past of more extreme climatic events which, however, did not produce significant slope movements. The review of Caramanico landsliding history suggests that when determining the regional or even local thresholds a clear distinction must be made between man-modified and true natural slope settings. It appears, however, that for all practical purposes, the site-specific prediction of landslide occurrence in mountainous environments will remain a difficult task. From a geolosit's perspective this is due to the fact that the subsurface geology of slopes in mountainous regions (and thus their hydrological response to rainfall events) is tipically more complex and less understood as compared to other environments.