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F. Pepe et al. / Geomorphology 303 (2018) 191–209 195

Fig. 2 (continued).

The obtained conventional radiocarbon ages were subsequently cal- 3.6. Numerical hydrodynamic analysis
ibrated by using the OxCal Ver. 3.10 software (Reimer et al., 2013). We
used the reservoir correction: ΔR = 58 ± 15 years as the average value Numerical hydrodynamic analysis is based on Nandasena et al. (2011)
for the Mediterranean Sea. The curve of the radiocarbon concentration equations, which relates to forces acting on a boulder impacted by a
relate to the West Mediterranean sea for the period 1949–1998 wave. We assume that drag, lift, restraining, gravity and inertia are forces
(Tisnérat-Laborde et al., 2013) was used as a reference to calibrate applied to the boulder when subjected to water flow. Overall, the interac-
the age of samples having a radiocarbon concentration corresponding tion between forces is strongly influenced by the pre-transport position
to a ‘post-bomb’ sample (i.e. a sample which incorporated the anthro- of boulder. In particular, when the pre-transport position of block is
pogenic radiocarbon released by the nuclear atmospheric detonation sub-aerial the inertial force is evaluated, whereas when it is submerged
tests carried out after the Second World War). Specifically, the the drag and lift forces due to impact of waves and the restrain force of
calibrated calendar age is obtained by graphic interpolation. This ap- the boulder are considered. In both settings it is appropriate to balance
proach intrinsically takes into account both the local and marine reser- the forces in the lifting direction, which is perpendicular to the rocky plat-
voir effects. form, when the blocks are detached from a rocky platform (joint bounded
scenario). In this case, it is assumed that the drag and inertia forces are
not imposed effectively on the boulder because adjacent rock faces
3.5. Bathymetric data cover it. In addition to different pre-transport settings, Nandasena's equa-
tions estimate flow velocity needed for different types of movement (i.e.
Due to the lack of digital chart, bathymetric data around sliding, rolling or saltation) and consider the effect of slope.
Favignana Island were obtained by digitizing isobaths and shoreline Both free submerged and joint bounded pre-transport conditions are
of the nautical chart “Litorale da Trapani a Marsala e Isole Egadi”,at a considered for each boulder. We applied the following Nandasena's
scale of 1:50,000, by using the QGIS V. 2.18 software. The data were equations, which are differentiated based on their initial transportation
stored in a 3-columns ASCII table: longitude, latitude, and depth in mode, for submerged scenario:
meters in order to obtain a depth matrix used to derive the slope of
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the sea bottom. The bathymetric data were also gridded in order to • Sliding u ≥ 2·[(ρs/ ρw) − 1] ·g·C·(μ s ·cosθ +sinθ)/ [c d ·(C / B)
obtain a regular 15 m-spaced DigitalElevationModel(DEM), by + μ s ·C l ];
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using the Global Mapper software. Fig. 1A shows the shaded relief • Rolling/overturning u ≥ 2·[(ρs/ ρw) − 1] · g ·C·[cosθ + (C / B)sinθ]
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and contour map for the Favignana Island offshore based on the /[c d ·(C /B )+ c l ];
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15 m cell size DEM. • Saltation/lifting u ≥ 2·[(ρs/ ρw) − 1]·g·C·cosθ /c l .