Authors' reply to discussion by I. Yilmaz on “Development and morphometry of sinkholes in coastal plains of Apulia, southern Italy. Preliminary sinkhole susceptibility assessment” [Engineering Geology 99 (2008) 198–209

Abstract

The authors would like to express their thanks tothe discusser IsikYilmaz for his interest in our paper and the related comments. In thisreplywepresentourexplanations,hopingthattheywillhelptoclarifythe points raised by the discusser.Asapremise,wehavetopointoutthatApulia,aregionwherekarstisamongthemainprocessesactinginevolutionofthelandscape,bothat the surface and underground, dedicates institutionally very scarceattention to karst hazards, which results in high degradation of theterritory,withadverseconsequencesonthequalityofkarstwatersandloss of peculiar karst landscapes (Parise and Pascali, 2003). Recentstudies, dedicated to evaluating the degree of disturbance to the karstenvironment by applying a specifically-created Karst DisturbanceIndex (Van Beynen and Townsend, 2005), demonstrate that Apuliankarstismoderatelytohighlydisturbed(CaloandParise,2006;Northetal., 2008). This is an extremely severe situation for a karst territory,since karst is known as one of the most fragile environment in theworld, extremely vulnerable to pollution and susceptible to a numberof geo-hazards (Waltham et al., 2005; Fordand Williams, 2007; Pariseand Gunn, 2007). As regards to sinkholes, Apulia presents all thetypologies of sinkholes, well distributed in the different parts of theregion (Delle Rose et al., 2004), in part also related to anthropogenicactivities,astherecentcaseregisteredinApril2007atGallipoli,whereaseveralmetersdeepsinkholeopenedinafewhoursinthetown,dueto presence of ancient underground quarries. Luckily, the collapseinterested a street crossing, only marginally affecting buildings, andnobody was injured.Notwithstanding this situation, there is no study at the regionallevel aimed at recognizing the presence of sinkholes and the hazardthey pose to the human society. Only recently, in 2006, as we havereported in the Conclusions of our article, the Apulian Regional BasinAuthority issued an act dictating rules to be followed in areas exposedto underground cavities and/or sinkhole hazard.The first aim of our work was, therefore, to raise the attention onthis very subtle hazard, at the same time performing a preliminaryattempt (we will return to this, further on) in developing a sinkholesusceptibility map.We agree with the assumption that, in the attempt to identifycollapse-susceptibleareas,themainfactorsleadingtocollapsehavetobe analyzed first (Upchurch and Littlefield,1988; Benson et al., 2003;Hubbard,2003;Brinkmannetal.,2008),sinceitisexpectedthatfuturecollapses will occur under the same conditions as past collapses.Actually, our study started from characterization of the main factorsinvolved, and the deriving results were presented in Section 4“Morphometry”. There, in particular, size, depth, slope, distance from