**5. Discussion and Conclusions**

Overall data highlight the complex geological, geomorphological and morphostructural setting of the Coroglio-Trentaremi sea cliff, which is carved in volcanic deposits whose ages range between 20 ka and the present. The main volcanic units are made up of both loose (mainly ashy and sandy) and lithified deposits (generally tuffs). The contact between the different volcanic units is characterized by volcano-tectonic collapses and erosional surfaces locally marked by paleosols, which also control the bedding of strata. All these conditions represent significant predisposing factors for selective erosion and, consequently, for cliff instability.

The lithified deposits are affected by a pervasive system of sub-vertical faults and fractures, mainly NE-SW and NW-SE trending, which may favor the occurrence of landslides. We recognized five systems of fractures, a finding that is consistent with geostructural analysis along the Coroglio cliff by Matano et al. [16]. The interaction between bedding and fracture' systems determine the failure mechanism, which mainly consists of rock fall and toppling that may involve up to some hundreds or even thousands of cubic meters of material.

Landslide type and related volumes are consistent with detailed topographic data produced by Caputo et al. [64] along the Coroglio sea cliff, who recognized rock fall, debris fall, earth flow and soil slip that caused, in the 2013–2015 time span, the accumulation of 210 m<sup>3</sup> of material. Furthermore, Caputo et al. [64] also estimated average cliff retreat in the 2013–2015 time span to be of 0.07 m/yr.

The cliff zonation that we propose in this study is based on an empiric geomorphologic approach and considers a high quantity of field data. We know that it is not exhaustive and that to better define the landslide risk, further investigations are necessary. Nonetheless, it may enable the development of a reliable scenario of cliff instability, which may be useful either to plan intervention works in the most critical areas or to organize prevention plans aimed at risk mitigation.

The studied coastal segments surely have high naturalistic and historical value, including the beautiful bays of Coroglio, Trentaremi and, at the top of promontory, the Pausyllipon- La Gaiola archaeological site and the Virgiliano urban park.

Our study pointed out that, at some points, landslide niches are quite close either to some important archaeological remains, such as the Roman villae of Diana near the Trentaremi bay, or to touristic areas, such as the Virgiliano Urban Park on top of the Coroglio cliff, also showing evidence of cliff retreat (Figure 12). These data suggest that these sectors deserve mitigation intervention to prevent damage to people and to man-made structures, and to preserve this unique and peculiar site for future generations.

**Author Contributions:** Conceptualization, A.S. and G.D.C.; methodology, A.S. and G.D.C.; software, E.V.; validation, A.S. and N.S.; formal analysis, E.V.; investigation, A.S., G.D.C., N.S. and E.V.; writing—original draft preparation, A.S., N.S. and E.V.; writing—review and editing, A.S., N.S. and E.V.; visualization, G.D.C.; supervision, A.S. and N.S. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** The authors wish to thank three anonymous reviewers whose suggestions helped us to improve the manuscript.

**Conflicts of Interest:** The authors declare no conflict of interest.
