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The Costa target areas exhibit the variability of slope instabilities needed to improve our understanding of sediment physical and mechanical properties in areas prone to sliding. That is why in this project, we have analysed the different slope failures events from different parts of the Costa target areas, which reflect diverse triggering mechanisms. The aim of the first part of this study was to identify the geotechnical response of the sediment to different external mechanisms (earthquake, rapid sedimentation and gas hydrate melting). We have focused on the relation between external mechanisms and the consequence change in the in-situ stress state and the physical, mechanical, and elastic properties of the sediment.In the second part of the paper, the geotechnical properties of the sediment from different Costa areas are presented. Comparison between observed geotechnical properties and the theoretical behaviour was done in order to improve our understanding of the origin of the different observed slides. D

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Clinoforms on modern shelves and slopes, as well as in ancient rock records, are widely recognized as a fundamental building element of continental margin growth. Regardless of their dominant lithology, clinoforms are composed of three geometric elements: topset, foreset and bottomset. Traditionally, much emphasis in the study of clinoforms was put on the geometry of the topset, viewed as the most energetic portion of a clinoform and studied to discern if aggradation was active rather than erosional truncation, and on the foreset, the area with the highest sediment accumulation rates. Here we focus on the factors forcing clinoforms to taper out and on the inferred mechanisms for bottomset creation. We base our analysis on muddy shelf clinoforms, a particular class of clinoforms that is typical of low-gradient settings and is characterized by a substantial component of shoreparallel sediment transport. This paper is based on a large dataset of CHIRP-sonar profiles, bathymetric and isopach maps of the Late Holocene clinoform on the Adriatic shelf, where integrated stratigraphic studies from sediment cores allow a very high (in some cases century-scale) chronological resolution. Knowledge on the dominant oceanographic regime affecting sediment dispersal and, ultimately, clinoform development, has been recently refined during the EuroSTRATAFORM collaboration. Muddy clinoforms are markedly three-dimensional features that cannot be entirely understood solely on two-dimensional shore normal sections. We suggest that this class of clinoform is advection dominated and that an increase in the energy regime at the toe of the foreset may prevent sediment from reaching beyond the transition to the bottomset region.

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This multidisciplinary case study of two preserved barrier systems combined the analysis of radiocarbon datings, grain-size distributions, high-resolution seismics, and shelf bathymetry with reconstructions of palaeo-environmental conditions (tides, waves, sea-level change) and forward modelling of barrier-lagoon systems, to provide an integrated view of the coastal transgressive evolution of a large sector of the northern Adriatic shelf between 15 and 8 ka BP. Palaeoenvironmental reconstructions point to increased tidal amplitude, low-energy wave climate and high rates of sea-level rise (up to 60 mm/a) during the formation of the oldest preserved barrier system (not, vert, similar90 m water depth; 14.3 cal ka BP). A younger barrier system (42 m water depth; 10.5 cal ka BP) formed under conditions of lower tidal amplitude, higher wave energy and a lower rate of sealevel rise (10 mm/a). Forward modelling suggests that the probability of barrier-island overstepping during transgression is inversely proportional to tidal amplitude, if all other factors are assumed equal. The oldest barrierlagoon system developed under conditions of large tidal amplitude, which permitted rapid transgression. However, this system apparently failed to keep up with the anomalously high rate of sea-level rise resulting from melt-water pulse 1A. The youngest barrier system appears to have drowned in place due to antecedent topography. As the barrier system transgressed over an ancient Pleistocene alluvial plain, the rapid increase in backbarrier accommodation caused an abrupt disequilibrium between shoreface and backbarrier sedimentation, which led to barrier overstepping. Although BarSim modelling indicates that tidal deposition can reduce the probability of barrier overstepping, there are other driving mechanisms (in our case extremely rapid sea-level rise and antecedent topography), which are more determinative in explaining the transgressive coastal evolution of barrier-lagoon systems in the northern Adriatic Sea. Grain-size analysis of shoreface deposits sampled above the transgressive ravinement surface across the northern Adriatic shelf indicate a distinct relation between the sediment grain size and the rate of sea-level rise during deposition, which implies that progressive sorting must have been highly effective.

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