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Abstract: Piping (tunnelling) appears to be one of the more significant methods of erosion in the badlands in the Plio-Pleistocene marine-sourced clays of the Basilicata area in Southern Italy. A detailed field investigation of the pedological, textural, mineralogical and geochemical properties of the clay-rich terrains widely outcropping in two selected badland field sites (the Fossa Bradanica area and the Bacino di Sant''Arcangelo) was undertaken to further elucidate process variability across the complex site. Paralleling findings from other piped badlands, certain physico-chemical properties of the clays were found to influence the different erosional processes in fundamental ways. The very dispersive nature of the materials enhances pipe enlargement so that subsurface flow rapidly becomes the dominant process, causing pipe enlargement by a process of positive feedback. The paper speculates on the progressive role of surface and subsurface processes in the genesis of all evolutional badland forms (calanchi, calanchi mammellonari and biancane). In an early stage, the calanchi mammellonari are produced, as slope mounds become increasingly separated by a dense network of small inclined pipes in the intermediate part of the slopes, a site which is presumed to favour elevated subsurface flow. When the overburden collapses, many cones are isolated in these portions of the slope. A second stage follows in which overland flow dominates, with the water canalizing into small gullies generated by the collapsed crust. At the base of many slopes, this same mechanism produces biancane as residual cones. Because of the structural weakness of piped materials, mass movements cannot be ruled out. In a few locations, landsliding may be involved, especially in the formation of calanchi mammellonari. In this case the intersection of the vertical pipes with the impermeable substratum focuses subsurface flow, and collapse of the surface along this failure plane. Subsequent remodelling occurs by surface processes, since the ‘catchment volume’ for large pipes no longer exists. This interpretation differs from that of others who have argued that in other locations the biancane formation is linked to the development of large vertical pipes along tectonic joints. [Copyright &y& Elsevier]