Geologica Romana 37 (2003-2004), 113-121

MORPHOLOGICAL CONTROL ON SEDIMENT DISPERSAL ALONG THE SOUTHERN TYRRHENIAN COASTAL ZONES ()

Tommaso De Pippo, Carlo Donadio & Micla Pennetta

Dipartimento di Scienze della Terra, Università degli Studi di Napoli Federico II e-mail: [email protected]

ABSTRACT - The study shows the relationship between the coastal zone, the continental shelf-slope system morphology and the sediment dispersal with respect to the coastal dynamics. Three areas along the Tyrrhenian margin are studied: the Gulf of Policastro, the Gulf of Gaeta and the Volturno River mouth. A sedimentological analysis, using also quantitative techniques for sediment distribution and classification, was carried out on bottom samples collected from the Gulf of Policastro in order to identify the morphological control on recent and present-day sediment dispersal. The sediment distribution which derives from cluster analysis shows that the morphological characteristics are related to sedimentary trends. In fact, the groups identified by multivariate statistical analyses evince that the dis- tribution and deposition of sediments are strongly conditioned by the morphology of the area as well as by mor- phodynamic evolution of the main structures. The study of sediment properties, collected from the shelf and the slope of the Gulf of Gaeta, as well as the hydrologic data registered during oceanographic surveys in the area, show that they are related both to the emer- ged and submerged coastal morphological features. The water circulation in this littoral, which mainly determines sediment distribution, shows two separated regi- mes close to the shelf break: a coastal regime, characterised by the formation of secondary cells, and an offshore regime, dominated by the cyclonic gyre of the Tyrrhenian Sea. This differentiation is related to the features of the coastal zone, where three morphological elements affect the circulation: the headland of Gaeta, the structural high to the S of the headland and the area near the shelf break. The modal analysis carried out on the samples collected on the sea bottom in front of Volturno delta complex enabled to identify the presence of 5 granulometric subpopulations and to define their participation degree in the coastal dynamics, as well as to identify the sedimentary transit axes along the entire littoral. The research carried out in front of the Volturno River mouth, in accordance with the analysis of modal isodensity curves, has demon- strated that the sediments move along directions defined by the sea bottom morphological trend.

KEY WORDS: Coastal geomorphology, submarine geomorphology, sediment dispersal, seawater dynamics, eastern Tyrrhenian margin, .

INTRODUCTION ly of Volturno rivers. The gulf represents the northern submerged sector of the Campania Plain, a wide coastal Studies on sediment deposition and dispersal rarely tectonic depression delimited to the E by the Apennine take into account the influence of coastal and gulf mor- chain, originated during the lower Pleistocene. phology. Therefore, this research carried out in three This subsiding coastal graben is filled with thick con- areas along the Tyrrhenian margin (the Gulf of tinental, transitional and marine deposits of Quaternary Policastro, the Gulf of Gaeta and the Volturno River age, interbedded with volcanic sediments from Phlegrean delta) intended to show this important control operated Fields, Somma-Vesuvius and Roccamonfina vents. by the coast, the continental shelf and the slope, under- Finally, the third area is the Volturno River mouth, to lining the relationship between the coastal zone, the con- the S of the Gulf of Gaeta, where the same gently slop- tinental shelf-slope system morphology and the sedi- ing continental shelf is characterised by two orders of ment dispersal, also related to the seawater dynamics. sand bars close to the coastline and by the submerged The southernmost area studied is the Gulf of Policastro, river mouth complex down to - 120 m depth, which is located between the southern Apennine chain and the related to the relict morphology of the late würmian river Tyrrhenian basin. mouth. The Plio-Quaternary uplift, the intense tectonic activi- ty of the Calabrian Arc and the synchronous subsidence of the Tyrrhenian basin governed the complex and var- GULF OF POLICASTRO ied morphology of the Tyrrhenian margin of this area. The physiographic setting of the seabed is conditioned A sedimentological analysis, using also quantitative by morphostructural highs, basins and channels which techniques for sediment distribution and classification, resulted from extensional tectonic activity producing was carried out on bottom samples collected from this step-like blocks sloping down northward and seaward. gulf in order to identify the morphological control on The second and northernmost area is the Gulf of Gaeta, recent and present-day sediment dispersal. furnished by sediment supply of Garigliano and partial- This area (Fig. 1) is characterised by sectors with a 114 Geologica Romana 37 (2003-2004), 113-121 DE PIPPO et al.

Fig. 1 - The Gulf of Policastro, located in front of the Calabrian Arc and tectonically still active. The gulf is characterised by two different subma- rine morphological sectors: the first with a narrow continental shelf and a -90 m deep shelf break, the second with a wide platform and a -130 to - 140 m deep shelf break. The inherited and present-day morphologies identified along the continental shelf and the slope both control and are recip- rocally influenced by the sediment dispersal. A, B, C, D, E and F represent different cluster groups of sea bottom sediments. narrow continental shelf (less than 3 km), with a -90 m Beyond the shelf break, on the upper slope, variations deep shelf break, and sectors where the continental shelf of inclination due to the presence of marine terraces at is 8 km wide with a shelf break -130 to -140 m deep (De different depths were observed. The upper slope devel- Pippo & Pennetta, 2000). ops with very steep stretches where the shelf is narrow- MORPHOLOGICAL CONTROL ON SEDIMENT ... Geologica Romana 37 (2003-2004), 113-121 115 er, whereas it declines with a gentle slope in correspon- Cluster F: it includes silty-clayey sediments collected dence to the areas where the rivers to the S of the gulf at the base of steeper slopes in correspondence to the debouch. In the latter, the instability phenomena (creep, narrower shelf. Their textural characteristics suggest landslides) are less frequent than in other areas where massive transport (turbidites, creep, etc.). they contribute to shelf break retreat. The morphology of the upper slope, down to the depth The sediment distribution which derives from cluster of -1100 m, is characterised by slope ridges, basins and analysis shows that the morphological characteristics are canyons (Selli, 1970; Selli & Fabbri, 1971; Fabbri et al., related to sedimentary trends. In fact, the groups identi- 1981). The ridges, that reach -280 m depth, are isolated fied by multivariate statistical analyses evince that the and/or aligned according to the structural trend of the distribution and deposition of sediments are strongly Tyrrhenian margin. At the same time they are cut conditioned by the morphology of the area as well as by through by tectonic lines in which the greater canyons morphodynamic evolution of the main structures (De have been scoured. Pippo & Pennetta, 2000). The Basin of Sapri is located in the northern sector of Coarser sediments of cluster A and B are present in the the study area; it is partially limited seaward by the inner portion (<-50 m) of the southern larger continental ridges and landward by a steep slope dissected by many shelf. More specifically, the sediments of cluster A have canyons. The latter, as evidenced by the contour lines a parallel distribution to the coastline with a convexity in and the bottom morphology, would constitute the tribu- correspondence to the river mouths, confirming a clear taries of the basin, while the effluent would open west- connection with the fluvial supply (Fig. 1). ward between the ridges reaching the base of the slope Whereas, sediments of cluster B, showing a scattered (Cocco & De Pippo, 1988). distribution, are autochthonous sediments deriving prob- The sedimentological analysis was carried out on 85 ably from bioclasts, found to the S of the study area. bottom samples collected from the continental shelf and Also cluster C gathers samples collected from the con- the slope (Fig. 1). The data elaboration was developed tinental shelf, mainly in the narrower and steeper north- according to statistical methods (Davis, 1973; Poluzzi et ern areas, secondarily from the wider shelf deeper than - al., 1985) of multivariate analyses (cluster analysis). 50 m. The textural characteristics and the sediment dis- Cluster analysis enabled to identify 6 sediment groups: tribution observed along this border, indicate high ener- gy processes related to waves and currents. These Cluster A: this group is present down to the depth of - processes act on the finest fraction of the samples scat- 50 m. Textural parameters may reflect a deltaic supply or tering it toward the continental shelf. At the same time, a mixing of deltaic and marine sands, moderately to the sediments could be associated to relict deposits. poorly sorted and strongly fine-skewed; Other studies underlined similar sedimentary character- istics at same continental shelf depths (Aguado, 1973; Cluster B: this group is present where the continental Fabbri et al., 1981; Poluzzi et al., 1985; Argnani et al., shelf is wider. Microscopic analysis on calcarenite frag- 1989; De Pippo & Pennetta, 2000). ments (content of carbonate >75%) indicates that they The samples of cluster D represent the complex are related to autochthonous deposits (skeletal grains) of dynamics of the shelf break dominated by strong turbu- continental shelf; lence and/or intense currents able to hold the mud in sus- pension. Cluster C: this group is found in the narrower portions The sediments of cluster E indicate a biogenic and of the continental shelf and rarely in the outer portion clastic deposition. They are more frequent in the zones (>50 m depth) of the wider shelf. The textural character- where the continental shelf is wider and along the gen- istics indicate that the sediments grouped in this cluster tler slopes, where the currents deposit the finest fraction. generally were deposited in areas dominated by high- Finally, the characteristics of cluster F, composed of energy processes such as waves or currents. Mixing with very fine sediments, suggest mass flow processes. The relict sediments is suggested by the presence of well samples are located mainly at the continental shelf and rounded grains; of the submerged ridges.

Cluster D: these sediments, well sorted and negative- skewed, were collected from the shelf break and from GULF OF GAETA the top of the submarine ridges. Their presence might The coast between Gaeta and Cuma (Fig. 2), located in indicate a distal high-energy environment subject to correspondence to Garigliano and Volturno coastal rapid morphological changes; plains, is 65 km long and presents a NW-SE direction. Along the coast, sandy beaches alternate with tracts of Cluster E: this group, represented by silty samples, is rocky coast. Quaternary marine terraces are present in found mainly on gentle slopes and in correspondence to the continental area between +230 and +30 m and notch- the wider continental shelf characterised by slow depo- es at different heights (between +5.3 and +1.3 m) on the sition. Mixing with biogenic and prodelta sediments cliffs testify to ancient sea-levels (Ozer, 1987; Antonioli, indicates that mass flow deposition occurred; 116 Geologica Romana 37 (2003-2004), 113-121 DE PIPPO et al.

Fig. 2 - The Gulf of Gaeta, a wide depression originated during the lower Pleistocene tectonic events linked to the final uplift of the Apennines chain. Sea bottom sampling points are indicated: the sediments distributed along the inner shelf are mainly provided by the Garigliano River and subordi- nately by the Volturno River scarce supply. The coastal physiography and three main submarine morphologies strictly influence the present-day marine sedimentary processes of the gulf: the headland of Gaeta, the structural high to the S of the headland and the shelf break area.

1991; Brancaccio et al., 1991). period (Brancaccio, 1990). The continental shelf, gently tilted seaward, shows the The upper slope is affected by many canyons; the maximum of width in front of the Garigliano River Cuma canyon, probably corresponding to a fault, shows mouth (20 km) and the minimum one in correspondence headward erosion due to gravity-collapse and mass to Cuma (~10 km); the shelf break is located at -120/- flows. A submerged morphological headland is present 130 m depth. In correspondence to the present-day to the S of the Gaeta Promontory in correspondence to a prominent Volturno delta it is possible to identify a pro- structural high (Bartole, 1984). nounced seaward convexity of the isobaths related to the The circulation pattern of the Tyrrhenian Sea (Fig. 3), ancient mouth (Pennetta et al., 1998). The latter could be which influences the circulation in the study area, shows attributed to the maximum low-stand of the Würm. The the presence of a cyclonic vortex that interests both the marine terrace visible between -100 and -125 m depth to superficial (down to -10 m depth) and the intermediate the S of the Gaeta Promontory could be related to sever- (between -10 and -100 m depth) layers. This circulation al remodelling phases before and during the same glacial is more intense during winter, whereas in summer, it is MORPHOLOGICAL CONTROL ON SEDIMENT ... Geologica Romana 37 (2003-2004), 113-121 117

and to the presence of a front that separates the south- eastern zone (low salinity) from the northwestern one (high salinity) (Brown et al., 1979). At intermediate depth, the maximum of salinity is related to the presence of the LIW, coming from the eastern , through the Sicily Channel. Recent studies have shown that the LIW in the Tyrrhenian Sea results conditioned mainly by the bathymetry and it runs towards the Campania Region coasts (Hopkins, 1988). During oceanographic cruises, bottom sampling and hydrologic surveys were carried out. The samples are located along three profiles: one parallel to the coastline, between -10 and -50 m depth; the other two transverse to SW of the Garigliano River, between -26 and -272 m depth. Table I reports sedimentological (Folk & Ward, 1957) and physical characteristics of the studied samples. During the hydrologic surveys, meteorological data and measurements of surface currents were registered. The results of this research suggest that the dynamics known represents a reliable indication of the present-day dynamics for major depths (Budillon & Moretti, 1994). Sediment distribution along the parallel profile shows a great fluvial control close to the mouth of the Volturno River and a decreasing influence in the adjacent portions due to coastal dynamics (waves and currents). For the sediments collected along the profiles perpen- dicular to the coast it is possible to distinguish three areas: the first area is characterised by sediments of con- tinental shelf (<-50 m), composed essentially of coarse- medium silt with a sand fraction between 2.5% and 14% (Tab. I); the second one, with samples collected at -120 m depth (shelf break), shows a prevalence of fine and clayey silt with an anomalous percentage of sand (between 5% and 40%) and coarse silt (between 56% Fig. 3 - Circulation patterns of the Tyrrhenian Sea and their influence on and 90%) sediments. This latter might be attributed to the circulation in the Gulf of Gaeta. A cyclonic vortex interests both the relict sediments locally not covered by recent mud, prob- superficial (MAW) and intermediate (LIW) layers. In winter (a) this ably due to erosive effects of the currents. Finally, the type of circulation is more frequent, mainly with a NW seawater flow direction; in summer (b) the circulation preserves his cyclonic character third area is characterised by slope samples that show but is interested by smaller cells and reduced dynamics, with S and SE- equal percentage of coarse sandy-silty and fine silty- ward seawater movements. clayey sediments (Tab. I). These characteristics could be explained by the deposition of erosional relict sediments characterised by a reduced dynamics, although preserv- (coarser fractions) during a normal mud sedimentation ing his cyclonic character. The agreement between along the slope. geostrophic and wind-related circulation documents the The hydrodynamic processes recognised in this shelf importance of the eolic vector for the determination of break area are complex. Under the hydrodynamic point the dynamics of the superficial layers (Hopkins, 1988). of view, the oceanographic studies enabled to define two In the Tyrrhenian Sea, based on its thermohaline char- zones with two different circulation regimes in the Gulf acteristics, three main masses of water can be recog- of Gaeta: a coastal zone and an offshore zone (Fig. 3). nised: the Modified Atlantic Water (MAW), the The first is mainly characterised by closed cyclonic Levantine Intermediate Water (LIW) and the Tyrrhenian and anticyclonic circulations and is separated, in corre- Deep Water (TDW). The MAW occupies the superficial spondence to the shelf break, from the latter, mainly layer of the water column and is characterised by low interested by a northern flow. salinity. This fact is due to the penetration and modifica- In winter (Fig. 3a), the main water flow is from the S tion of the Atlantic water through the Strait of Gibraltar. and it moves along the shelf break forming secondary The pattern of the isohaline lines, mainly parallel to cells in correspondence to the main rivers due to the the coastline, suggests that the MAW is not affected by obstacle created by the Island. On the contrary, in important mixing phenomena running northward. In summer (Fig. 3b), when flows are from the N, the water summer, the situation is substantially different both due circulation is influenced by the coastal morphology and to the numerous vortexes that characterise all the basin by the presence of the submerged morphostructural 118 Geologica Romana 37 (2003-2004), 113-121 DE PIPPO et al.

sample (n°) sand (%) silt (%) clay (%) FOLK’s definition s I (f) KG SK I CaCO3 (%) 1 1.28 96.1 2.1 medium silt 0.682 1.279 0.101 45.773 2 1.34 94.03 4.53 medium silt 0.823 1.623 0.242 58.662 3 0.72 92.73 6.17 fine silt 0.738 2.72 -0.013 53.816 4 0.9 94.1 5 fine silt 0.811 1.906 -0.489 53.704 5 2.54 89.95 5.82 fine silt 1.048 1.663 -0.137 64.675 6 5.13 90.32 4.08 medium silt 1.13 1.25 -0.363 55.55 7 6.5 79 14.5 fine silt 1.608 0.786 -0.366 54.727 8 2 88 10 fine silt 0.789 2.943 -0.118 57.377 9 40 56 4 medium silt 2.323 0.673 -0.476 47.243 10 27 70 3 coarse silt 1.578 1 -0.538 39.5 11 1.97 84.99 12.81 medium silt 1.305 1.078 -0.146 54.078 12 8.08 86.19 5.59 medium silt 1.331 1.68 -0.447 58.676 13 1.26 97.55 0.57 medium silt 0.653 1.136 0.019 61.202 14 7 92.48 0.5 fine silt 0.881 2.957 -0.264 59.817 15 8.18 88.34 1.98 coarse silt 0.823 1.386 0.196 32.335 16 8.6 88.65 2.69 medium silt 0.844 1.309 0.056 30.153 17 9 90.53 0.41 medium silt 0.859 1.132 -0.111 39.97 18 1.73 93.8 3.23 medium silt 0.631 2.357 0.165 35.65 19 5.42 93.89 0.69 medium silt 0.873 0.81 -0.305 46.121 20 2.53 89.92 5.44 medium silt 1.097 1.864 0.313 46.837 21 6.48 91.61 1.36 coarse silt 0.781 1.502 -0.212 40.699 22 4.6 90.78 2.76 medium silt 0.985 1.882 0.158 36.764 23 13.58 82.02 2.79 coarse silt 1.047 1.701 0.264 22.664

Tab. 1 - Textural and physical characteristics of bottom sediments collected from the Gulf of Gaeta; SI: standard deviation; KG: kurtosis; SKI: skewness. headland located to the S of the Gaeta Promontory. is also influenced by the effect of the Gulf of Gaeta and However, currents in coastal areas are less intense than the protection operated by the Gaeta Promontory. in the offshore when they are interested by the northern branch of the southern Tyrrhenian Sea circulation. Secondary cell circulations form on the continental VOLTURNO RIVER MOUTH shelf, whereas the flow of the Tyrrhenian cyclonic vor- A morpho-sedimentary study was carried out in corre- tex mainly acts on the slope. The latter changes direction spondence to the Volturno River delta by bathymetric near the terraced surface to the S of the promontory, survey and sampling of bottom sediments. The morpho- forming a secondary cell. This circulation amplifies the logical trend of the sea bottom (Fig. 4) indicates the erosive processes near the shelf break, mainly on the presence of two orders of submarine sand bars in the northernmost transverse profiles. The sediments show northern area of the mouth. A -5 m deep trough divides characteristics related to sandy deposits (high percent- the outer bars, situated parallel to the coastline, from the ages of sand and CaCO3), in accordance with literature. more irregular inner ones, located transversally to the The present-day reduced thickness of the mud in the shoreline (Cocco & De Pippo, 1988). Only a single area near the shelf break favoured the partial removal order of bars is present to the S of the mouth, extending and reworking of the relict transgressive sediments with a regular trend in an arrangement parallel to the caused by the hydrodynamic forces. At greater depth, the shore, with a ridge generally located at -3 m depth and offshore flow contributes to the shifting of finest fraction separated from the shoreline by a trough about -5 m from the slope sediments, negative-skewed. deep. The study of the variations in textural characteristics In correspondence to the mouth there is a very wide enabled to individualise a proximal sector, -10/-50 m bar that could be linked to the outer bars, although its deep, and a distal one at a major depth (>-50 m), both section presents an asymmetry of the flanks much less dominated by coarser sediments. Between the two, marked than the other bars. In addition, the irregular another sector dominated by the finest fractions with trend of the bathymetric lines indicates a rather distinct transitional features is present (Pennetta et al., 1998). submerged river mouth complex, with some weak inci- The dynamics down to -50 m depth is related to the sions in the flanks, located in correspondence to the flat or gently inclined morphology of the continental slight depression of the outer bar ridges and in axis with shelf and to the secondary cell circulations. It shows a the greatest depth points of the troughs. sediment distribution with finest fractions seaward, in a The right bank of the mouth is characterised by the sector of the continental shelf bounded by the Gaeta presence of a deep channel longitudinally arranged to Promontory. This dynamics is controlled by the interac- the river, while the left bank by a bar at -1.5 m depth. In tion of the fluvial processes and the swell. Moreover, it accordance with the technique tested by Aguado (1973), MORPHOLOGICAL CONTROL ON SEDIMENT ... Geologica Romana 37 (2003-2004), 113-121 119

Fig. 4 - The Volturno River mouth, located to the S of the Gulf of Gaeta. The sea bottom, in front of the present-day delta, is characterised by two orders of sand bars along the inner and flat platform dominated by waves, longshore and rip currents. The bars are parallel to the coastline and cut transversal- ly by channels.

Barusseau (1973), Pauc (1973) and Long (1975), the DISCUSSION AND CONCLUSIONS modal analysis carried out on the samples collected on Morphological research and analysis of textural charac- the sea bottom in front of Volturno delta complex teristics of bottom sediments carried out along three areas enabled to identify the presence of 5 granulometric sub- of the Tyrrhenian coast enabled to define the present-day populations and to define their participation degree in processes and their evolution in time and in space. the coastal dynamics, as well as to identify the sedimen- The relationship between such processes and seabed tary transit axes along the entire littoral. Only 4 of the 5 morphology were also identified, as well as the wave subpopulations are important in littoral dynamics: two formations which affect the coast and the complex sys- of medium sands, one of fine sands and a last one of tem of sediment transport. The interaction of coastal and very fine sands. Whereas the fifth, being quite absent, is submarine morphology with the hydrodynamic regimes not significant. determines a control on coastal dynamic processes, con- The analysis of modal isodensity curves (Cortemiglia, ditioning the dispersal of sediments in the three selected 1978) related to the materials which actively take part in areas. the littoral dynamics demonstrated that the medium Generally the hydrodynamic processes, under similar sands are essentially shifted by beach drift (Fig. 5a) morphological and hydrological conditions, produce sea and/or by longshore currents (Fig. 5b). bottom deposits with similar sedimentary features. Fine sands are moved by longshore currents parallel Whereas, in the three coastal zones under study, charac- to the coastline, to greater depths than medium sands terised by different sea bottom morphologies each one and sometimes shifted offshore by rip-currents (Fig. 5c). controlled by a specific coastal physiography, a different Whereas, very fine sands are exclusively carried off- response to sedimentary processes is observed. shore by rip-currents which move along directions Consequently, the evolution of submarine morpholo- defined by the morphological trend of the sea bottom gies like bars, structural highs, submarine ridges, (Fig. 5d). In fact, the shifting of very fine materials off- canyons and sea bottom depressions, is closely and shore occurs where troughs reach their greatest depth mutually controlled by the influence of these forms, both due to the deepening of the bar ridges. inherited and of new genesis, on sediment dispersal. Considering that the load transport of the Volturno In particular, within the submerged sector of the Gulf River has been estimated nearly non-existent because of of Policastro, still tectonically active and generally char- an artificial dam (Traversa di Ponte Annibale) close to acterised by a narrow and steep continental shelf, there the river mouth and that the littoral is in recession since are sediment groups strictly connected to the morpholo- 1909 at a medium rate of 19 m/year (Cocco & De Pippo, gies of the area, to the morphodynamic evolution of their 1988), it is presumed that the materials involved in this main submarine structures and to the presence of sec- movement are eroded exclusively from the beaches and ondary cell circulations. The coarser fraction is distrib- the sea bottom near the river mouth. uted parallel to the coastline in the high-energy, flat zone 120 Geologica Romana 37 (2003-2004), 113-121 DE PIPPO et al. ved by longshore currents parallel to the coastline, greater depths than medium sands rrents moving along directions defined by the morphological trend of sea bottom (d), sea bottom are based on the analysis of modal isodensity curves. Medium sands (0.461-0.346 mm) are shifted mostly by beach drift (a) and/or (0.344-0.250 longshore currents (b). Fine sands (0.248-0.128 mo by rip-cu fine sands (0.121-0.077 mm) are exclusively carried offshore Very by rip-currents (c). and sometimes carried offshore where troughs reach their greatest depth due to the deepening of bar ridges. Fig. 5 - Shoreface sampling points in front of the Volturno River mouth and littoral. Sediment drift patterns along the shallow Volturno Fig. 5 - Shoreface sampling points in front of the MORPHOLOGICAL CONTROL ON SEDIMENT ... Geologica Romana 37 (2003-2004), 113-121 121 of the inner platform, resulting mainly linked to fluvial both by coastal physiography and three seabed mor- supply mixed with marine sedimentation or occasional- phologies along the continental shelf: the headland of ly to biogenic sediments. These deposits and the related Gaeta, the structural high to the S of the headland and morphologies, sometimes associated to relict sediments, the area near the shelf break. are found both along the narrower and steeper zones and Finally, Volturno River mouth, characterised by a the deeper and wider shelf areas, where high-energy wide, shallow continental platform with a small present- processes due to waves and currents are observed. The day delta, a double sand bar strip and a reduced river fine fraction is frequently distributed both along the sediment supply, shows a littoral dynamics where medi- wider continental shelf and gently sloping areas, domi- um sands are moved by beach drift as well as by long- nated by currents, whereas the very fine sand fraction, shore currents. The latter also shift fine and sometimes found along the continental shelf and the submerged medium sands parallel to the coastline, whereas rip-cur- ridges, is related to massive flows. rents carry offshore exclusively very fine sands along The circulation in the Gulf of Gaeta, which controls directions defined by the sea bottom morphological the sediment distribution, shows two different regimes trend (bar channels). close to the shelf break. These are directly controlled

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