DTM-based morphometry of the Palinuro seamount (Eastern Tyrrhenian Sea): Geomorphological and volcanological implications
Introduction
Although about 60% of the Earth's volcanoes is located in the marine environment, detailed morphological data are still poorly available, because of the intrinsic difficulties of marine remote sensing. Nonetheless, detailed side-scan sonar imaging and swath bathymetry are useful tools in the analysis of guyots (Smoot, 1995), shoaling volcanoes (McPhie, 1995) and seamounts (Smith et al., 1997), and allow us to understand constructional and erosional processes and active structural and volcanic processes (Moore and Mark, 1992, Rowland and Garbeil 2000, Johnson et al., 2008). For example, the drainage pattern of volcanoes is often controlled by the presence of faults and dikes which, in turn, are responsible for and/or control collapse and spreading processes. In addition, reciprocal relations occur between the morphology of volcanic edifices, their substratum and the magmatic system (Thouret, 1999, and references therein).
In the last years, high resolution morphobathymetry (Mark et al., 1991, Gamberi et al., 1997, Marani et al., 2004, Gamberi et al., 2006 has been carried out in the Tyrrhenian Sea; the extensional back-arc basin located in the Central Mediterranean Sea. The recent multibeam bathymetric data acquired in the south-eastern Tyrrhenian Sea (Marani and Trua, 2002) has improved the knowledge on the Marsili Seamount, the largest ones in the Tyrrhenian Sea. This seamount, an almost linear edifice extending for about 55 km in the N15°E direction and characterized by a wide bathymetric range (3000–500 m), occupies the central sector of the Marsili ocean-like basin, the younger one of the Tyrrhenian Sea. The shape of this ocean-like basin is roughly circular and covers an area of ~ 8000 km2 with a flat seafloor located at 3500 m bsl depth on average. The location of the Marsili Seamount, its relief and morphological characteristics have been explained in term of a super-inflated spreading ridge (Marani and Trua, 2002). A few kilometres northeastward from the Marsili Seamount is the Palinuro Seamount, which is also one of the largest in the Tyrrhenian Sea (Fig. 1). Despite its location, at the transition zone between the Aeolian volcanic arc (considered to be the arc system of the Ionian subduction in the Central Mediterranean Sea), the Marsili back-arc oceanic volcanism and the Southern Italy passive continental margin, and notwithstanding its length (about 50 km along the E–W direction), this seamount has not been subject to intensive geophysical exploration and is the least known volcanic complex of the southeastern Tyrrhenian Sea. Specifically, although recent high resolution morphobathymetric surveys were performed in the Eastern Tyrrhenian Margin (Gamberi et al., 1997, Marani et al., 2004, Gamberi et al., 2006), high resolution DTM and morphological analysis of the Palinuro Seamount have not been undertaken.
During the geophysical survey carried out by IAMC-CNR in the southeastern Tyrrhenian Sea on board of the R/V Urania on November 2007, whose aim was to identify potential active volcanic and/or hydrothermal vents, high resolution multibeam swath bathymetry was performed on the Palinuro Seamount. Here, we present a new, high resolution Digital Terrain Model (DTM) of the Palinuro Seamount built from the acquired data. On the basis of this dataset coupled with geomorphological and morphometric analyses of the volcano complex, we provide new insight on the role of the Palinuro Seamount in the context of the eastern Tyrrhenian Margin. In particular, we focus on: a) the relations between different volcanic landform and depth variations and b) the structural features. Due to its particular location at the transition zone between different crustal provinces bordered by major faults and deformation zones, we believe that the morphological analysis of the Palinuro Seamount may offer new significant elements for a better understanding of the regional volcanism and geodynamic processes in the southeastern Tyrrhenian Sea.
Section snippets
Geological setting of the Palinuro Seamount
The Palinuro Seamount (0.8–0.3 Ma; Beccaluva et al., 1982, Beccaluva et al., 1985, Savelli, 2002; hereafter PS) is a volcanic complex located in the Tyrrhenian Sea (Fig. 1), a small extensional back-arc basin in the Central Mediterranean related to the subduction of the Ionian lithosphere below the Calabrian Arc in the context of the Africa–Eurasia convergence (Maliverno and Ryan, 1986). The opening of the Tyrrhenian Sea started about 11 My ago with an E–W-directed extension. This stage of
Data and methods
The geophysical survey for the present study was performed during the second leg of the “Aeolian_2007” cruise by the IAMC-CNR research institute (Naples, Italy) onboard the Urania oceanographic vessel in November, 2007. Multibeam data acquisition was carried out with the use of the Reson Seabat 8160 multibeam sonar system, which works well in the 50–3500 m depth range. The system, interfaced with a Differential Global Positioning System, is mounted on keel of the R/V Urania and is composed of a
Morphostructural features
The DTM of PS, with a depth range that covers the 3200–84 m below sea level (bsl) interval, is shown in Fig. 2, where a shaded relief image is reported. The DTM evidences a roughly elliptical shape extending about 55 km along N100°E and 25 km in the N–S direction. The morphology reveals a very articulated summit, characterized by different cone-like, flat and amphitheatre-like structures rather than a single volcanic edifice. Due to the structural complexity of the summit, we divide and separately
Morphological features and interpretation
The processed bathymetric data reveal previously unreported topographic features of PS both below 1000 m bsl and for the summit. The summit is very articulated and characterized by the presence of distinct volcanic structures. Unlike other seamounts that show almost continuous summit regions along their main axis (e.g. Marsili; Marani and Trua, 2002). The most important topographic features are found in WZ. The general shape of A and B, marked by a flat-topped surface and steep slopes of the
Morphometry and volcano-tectonic features
Unlike the Aeolian seamounts, PS has a very asymmetrical and elongated shape. In order to define properly its regional trends, we built a stack of profiles perpendicular (Fig. 5A) and parallel (Fig. 5B) to the main N100°E elongation of PS. The plot of results shows different erosional base level values both for E and W (1592 and 2750 m bsl, respectively) and for N and S (1872 and 2530 m bsl). This evidence can be easily interpreted taking into account that the wider PS structure is emplaced at
Discussion
According to McPhie, 1995, Head and Wilson, 2003, marine volcano products, variations in the eruption and fragmentation processes are influenced by water depth. The comparison between DTM, stack of profiles and a profile extracted over the ridge of DTM may clarify some aspects of the evolution of PS (Fig. 9). Differently from other sectors, WZ is characterized by concave profiles and strongly dissected morphologies bounded by ridges (caldera and craters) and volcano-tectonic depressions (Fig. 4
Concluding remarks
More than 1000 km2 of new multibeam sonar data have been processed and interpreted. Data interpretation has been coupled with morphometric analysis of a DTM. The main results of the work can be summarized as follows:
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PS is characterized by a roughly elliptical shape extending for about 55 km along E–W and 25 km in N–S directions. Its summit is very articulated and consists of a group of overlapped and/or coalescent volcanic edifices, that we have interpreted as a sequence of volcanic cones inside
Acknowledgments
We sincerely thank Guido Ventura and an anonymous reviewer for their helpful comments and suggestions and Andrew Plater, Editor, for the precious editorial handling.
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