Some evidence against the deep-seated gravitational slope deformation in Caramanico Terme (Abruzzo, Italy)

Abstract

The aim of this paper is to contribute to the discussion on the deep-seated gravitational slope deformations (Dgsd), by examining the case of the 1989 Caramanico landslide. The slide, which remobilized middle-lower portions of the slope capped by several tens of meter thick carbonate megabreccias, was originally interpreted as a deep movement linked to the Dgsd. In particular, several features, considered typical of a slope afflicted by Dgsd, were indicated in the zone upslope the main scarp of the 1989 event (series of scarps and uphill facing areas which appear to form trenches oriented parallel to the slope direction). The trenches were mapped upslope several carbonate breccia hills (hummocks), which in turn were interpreted as large blocks derived from the caprock plateau through a mechanism including deep-seated rotational failures followed by lateral spreading. A detailed examination of the area, integrated with subsurface data, has led to the re-assessment of the morphological features and to an alternative interpretation of the slope evolution, without invoking the Dgsd phenomena. To argue against the Dgsd hypothesis, we offer a series of geomorphological, geological, geophysical and geomechanical evidences; following these considerations, the several tens of meter thick surficial deposits, comprising the carbonate breccia hummocks in the middle-upper parts of the slope, may be interpreted in the context of an ancient alluvial fan setting, which subsequently suffered a considerable degree of post-sedimentary disruption. In particular, two carbonate breccia units can be distinguished within the hummocks. These breccias are separated by a succession consisting of debris flow, water-laid and sieve-like sediments (including a paleosol), and therefore, register the occurrence of at least two distinctive depositional events, probably generated by mass movements.