ORIGINAL RESEARCH PAPER
Submarine canyon morphologies in the Gulf of Palermo (SouthernTyrrhenian Sea) and possible implications for geo-hazard
Claudio Lo Iacono • Attilio Sulli • Mauro Agate •
Valeria Lo Presti • Fabrizio Pepe • Raimondo Catalano
Received: 9 April 2010 / Accepted: 18 February 2011 / Published online: 25 March 2011
� Springer Science+Business Media B.V. 2011
Abstract The continental shelf and the upper slope of the
Gulf of Palermo (Southern Tyrrhenian Sea) in the depth
interval ranging from 50 to 1,500 m were mapped for the
first time with Multi Beam echosounder and high resolu-
tion seismic. Seven submarine canyons are confined to the
upper slope or indent the shelf-edge and enter the Palermo
intraslope basin at a depth of around 1,300 m. The canyons
evolved through concurrent top-down turbiditic processes
and bottom-up retrogressive mass failures. Most of the
mass failure features of the area are related to canyon-
shaping processes and only few of them are not confined to
the upper slope. In general, these features probably do not
represent a significant tsunami hazard along the coast. The
geological element that controls the evolution of the can-
yons and induces sediment instability corresponds to the
steep slope gradient, especially in the western sector of the
Gulf, where the steepest canyons are located. The structural
features mapped in the Palermo offshore contributed to the
regulation of mass failure processes in the area, with direct
faults and antiform structures coinciding with some of the
canyon heads. Furthermore, the occurrence of pockmarks
and highs that probably consist of authigenic carbonates
above faulted and folded strata suggests a local relationship
between structural control, fluid escape processes and mass
failure. This paper presents a valuable high-resolution
morphologic dataset of the Gulf of Palermo, which con-
stitutes a reliable base for evaluating the geo-hazard
potential related to slope failure in the area.
Keywords Submarine canyons � Mass failure processes �Geo-hazard � Swath mapping � Southern Mediterranean
Introduction
In recent years, the analysis of high resolution swath map-
ping methods and shallow seismics have provided valuable
insights into Quaternary mass failure processes along sev-
eral continental margins around the world (McAdoo et al.
2000; Canals et al. 2004; Urgeles et al. 2006; Lo Iacono et al.
2008; Chaytor et al. 2009; Leynaud et al. 2009). The sci-
entific community has endeavoured to better assess the geo-
hazard due to submarine mass failure processes (McAdoo
and Watts 2004; Ten Brink et al. 2009; Waythomas et al.
2009). Apart from the tectonic processes, submarine land-
slides are one of the most common mechanisms associated
with geo-hazards, with a recognized potential for tsunami
generation (Canals et al. 2004; Ten Brink et al. 2009). Large
magnitude tsunamis, such as the 1998 Sissano Tsunami in
Papua New Guinea (Tappin et al. 2001), the 1929 Grand
Banks Tsunami in Newfoundland (Piper et al. 1999), and the
Storegga Slide of 7,950 yr BP (Bondevik et al. 1997) have
been attributed to submarine landslides.
In the Mediterranean Sea, landslide-generated tsunamis
can have a strong geo-hazard impact owing to the more
enclosed and shallow setting in which they propagate.
Well-known examples of both ancient and recent Medi-
terranean tsunamigenic landslides are the 2002 Sciara del
Fuoco landslide on the flank of Stromboli (Northeastern
Sicilian offshore) (Bonaccorso et al. 2003), the 1908
Submitted to Marine Geophysical Researches.
C. Lo Iacono (&)
Unidad de Tecnologıa Marina, UTM, CSIC, Paseo Marıtimo
de la Barceloneta 37–49, 08003 Barcelona, Spain
e-mail: [email protected]
A. Sulli � M. Agate � V. Lo Presti � F. Pepe � R. Catalano
Dipartimento di Geologia e Geodesia dell’Universita
di Palermo, Via Archirafi, 22, 90123 Palermo, Italy
123
Mar Geophys Res (2011) 32:127–138
DOI 10.1007/s11001-011-9118-0
Messina landslide (Northeastern Sicily), which generated a
tsunami that caused more than 6,000 casualties (Billi et al.
2008) or the Big 95 landslide, which occurred up to 10 kyr
BP in the Ebro margin (Northwestern Mediterranean) and
which generated a tsunami using theoretical models (Igle-
sias et al. 2011).
The type and frequency of mass failure processes are
commonly controlled by the interplay of different factors
such as tectonic activity (Hampton et al. 1996; McHugh
et al. 1998; Le Dantec et al. 2010), gas and fluid escape
(Bondevik et al. 1997; Greene et al. 2002, Popescu et al.
2004; Fuh et al. 2009) and slope undercutting (Pratson and
Coakley 1996; Baztan et al. 2005; Laberg et al. 2007).
Thus, the interpretation of the physical processes that
regulate mass failures constitutes the basis for the assess-
ment and monitoring of the geo-hazard potential in coastal
regions.
In the Gulf of Palermo (Northwestern Sicily, Central
Mediterranean), the application of swath-bathymetry and
high-resolution seismic profiles revealed the presence of
some submarine canyons. The main aims of this work are:
(1) to outline the morphology of the submarine canyons
and of the related mass failure features mapped in the
Gulf of Palermo, (2) to describe the main geological
processes that control mass failure and (3) highlight their
potential implications for the geo-hazard of the Gulf of
Palermo.
Geological setting
The Palermo Basin forms part of the northern Sicilian
continental margin (Fig. 1), in the transitional area between
the thick continental crust of the Sicilian-Maghrebian
Chain to the south and the thin, transitional-oceanic crust
of the Tyrrhenian Sea to the north (Nicolich 1985; Scar-
ascia et al. 1994). Following the deformation and thrusting
of the Kabilian-Calabrian tectonic units over the Sicilian-
Maghrebian tectonic units during the Miocene (Catalano
et al. 1985; Pepe et al. 2005), the opening of the Tyrrhenian
Sea led to the subsidence of the northern Sicilian margin in
the Late Tortonian (Bacini Sedimentari 1980; Fabbri et al.
1981). Extensional intra-slope basins, termed peri-Tyrrhe-
nian basins by Selli (1970), originated as a consequence of
crustal thinning. The Cefalu Basin is the largest of the peri-
Tyrrhenian basins, displaying a complex structural setting
(Wezel et al. 1981; Trincardi and Zitellini 1987). Bigi et al.
(1991) divided the Cefalu basin into an eastern sector
(Alicudi Basin) and a western sector (Palermo Basin). The
peri-Tyrrhenian basins were filled with Late Neogene to
Quaternary evaporitic, hemipelagic, siliciclastic and vol-
caniclastic deposits, with a maximum thickness of 1, 5 s t.
w. t. (Bacini Sedimentari 1980).
The Palermo basin has subsequently undergone com-
pressive/transpressive tectonic activity since the Late Pli-
ocene (Trincardi and Zitellini 1987; Agate et al. 1993;
Nigro and Sulli 1995; Del Ben and Guarnieri 2000). Tec-
tonic activity persists today with the occurrence of shallow
(\25 km) seismic events of low to moderate magnitude
(max Md 5.6 on September 2002; www.ingv.it; Gueguen
et al. 2002; Giunta et al. 2004) along an E-W trending belt
located northward of the study area. The focal mechanisms
related to the main seismic shocks are in agreement with a
dominant NE–SW fault trend coupled with a NW–SE
compressive offset direction (Agate et al. 2000; Lavecchia
et al. 2007; Giunta et al. 2009) (Fig. 1).
The continental margin is composed of: (1) a narrow
(\8 km) and moderately steep (1–2�) continental shelf, (2)
a very steep (7–8�) upper continental slope ranging in
depth from 150 to 1,000 m, (3) a flat intra-slope basin plain
at a depth of 1,500 m, (4) a lower continental slope that is
wider and gentler than the upper slope and (5) a bathyal
plain that starts from a depth of 3,000 m. The Gulf of
Palermo encompasses the shelf, the upper slope and intra-
slope basin and is enclosed between Cape Gallo to the
northwest and Cape Mongerbino to the East (Figs. 1, 2). To
the north, the basin is bounded by the La Barra spur, a
prominent morphostructural high made up of meso-
Fig. 1 Bathymetric map and on-land tectonic features of the Gulf of
Palermo (tectonic features modified from Abate et al. 1978; Avellone
et al. 2010). The upper left inset shows the location of the study area
within the Mediterranean Sea (red rectangle). The upper right inset
shows the earthquake epicentres mapped in the northwestern Sicilian
offshore (modified from Azzaro et al. 2004)
128 Mar Geophys Res (2011) 32:127–138
123
cenozoic carbonate rocks and topped by an irregular sur-
face at a depth of 65 m (D’Argenio 1999) (Fig. 2).
Seismic reflection data show a Plio–Quaternary suc-
cession of the Gulf of Palermo consisting of seawards
dipping clastic sediments, unconformably lying on a wide
erosional surface formed during the Messinian Mediterra-
nean desiccation (Fabbri and Curzi 1979; Pepe et al. 2003).
Seismostratigraphic data and cores collected in the Palermo
Basin and in the adjacent Cefalu Basin reveal a Plio-
Quaternary succession consisting of an alternation of
hemipelagic deposits with terrigenous turbiditic sediments
coming from the northern Sicilian margin (Fabbri et al.
1981; Pepe et al. 2003; Sbaffi et al. 2001, 2004). In the
continental shelf, the Pleistocene deposits are truncated by
an erosional surface formed during the last glacio-eustatic
sea-level oscillation above which lies a thin (\8 m) layer
of Holocene sediments (Agate et al. 1998; Pepe et al.
2003). Prograding sedimentary wedges of coastal deposits
formed during the Last Glacial Maximum (LGM) (*18 ky
BP) are present along the shelf margin (Pepe et al. 2003).
The prograding wedges are absent where the heads of the
canyons or landslide scars have indented the outer shelf
(Lo Iacono et al. 2005).
A ‘‘block faulted’’ structural setting has been recognized
on-land, where a morpho-structural depression filled with
Quaternary marine and continental deposits is bounded by
two prominent Meso-Cenozoic carbonate promontories,
Mount Pellegrino and Mount Catalfano (Abate et al. 1978)
(Figs. 1, 2). Normal and strike slip faults with main NE-
SW and N–S directions have been recognized in the area in
some cases cutting the Quaternary deposits (Avellone et al.
2010) (Fig. 1). Two long NNE-SSW trending rivers, the
Oreto and the Eleuterio, cross the Palermo coastal plain
(Figs. 1, 2). The orientation of these two rivers is struc-
turally controlled by NE-SW trending normal faults
(Figs. 1, 3b).
Materials and methods
Multi Beam data were acquired in the course of three
different oceanographic cruises in 2001, 2004 (CARG
cruises) and 2009 (MaGIC cruise) (Fig. 3a). During the
2001 cruise on board the R/V ‘‘Tethis’’, we used a Reson
SeaBat 8111 Multi Beam Echosounder (MBES). The
SeaBat 8111 generates 105 beams at a frequency of
Fig. 2 3-D shaded relief bathymetric map of the Palermo Gulf showing the main submarine canyons and morphostructures of the slope region.
The figure shows the correspondence between the Oreto River and the Oreto Canyon and the Eleuterio River and the Eleuterio Canyon
Mar Geophys Res (2011) 32:127–138 129
123
100 kHz for an operational depth range of 35–800 m.
During the 2004 and 2009 cruises on board the R/V
‘‘Universitatis’’, we used a Reson SeaBat 8160 MBES. The
SeaBat 8160 generates 126 beams at a frequency of 50 kHz
for an operational depth range of 30–3,000 m. Bathymetric
data were acquired and stored using the PDS2000 acqui-
sition software. Sound velocity profiles were collected with
the Navitronic Systems AS-SVP-25. Post-processing of
Multi Beam data was accomplished with the PDS-2000
system. Post-processing steps included the graphic removal
of erroneous beams, noise filtering, processing of naviga-
tion data and correction for sound velocity. Once cleaned,
gridding of the filtered soundings was carried out to obtain
the final Digital Terrain Model (DTM). DTM images were
produced with a footprint resolution of 15 m. The IVS
Fledermaus and the Golden Software Surfer 9 were used to
obtain 3D maps of the bathymetric data, shaded relief
maps, slope maps and bathymetric cross sections.
High resolution seismic profiles were acquired during
the 2004 CARG cruise (Fig. 3a) employing a multi-tip
sparker array, with a base frequency of around 600 Hz,
fired each 12.5 m. Data were received with a single-
channel streamer with an active section of 2.8 m, con-
taining seven high-resolution hydrophones recorded for
3.0 s two way time (TWT) at a 10 kHz (0.1 ms) sampling
rate. Data processing was performed using the Geo-Suite
software package running the following mathematical
operators: traces mixing, time variant filters, automatic
gain control, time variant gain and spherical divergence
correction. The resulting signal penetration exceeded
400 ms (TWT) and the vertical resolution reached 2.5 m at
the seafloor.
The seismic lines obtained were first interpreted using
seismic facies analysis tools and methods and then depth-
converted. We adopted an average velocity of 1,700 m/s
for the sedimentary units. This velocity was derived from
lithostratigraphy and sonic log data collected in the
southern and western Sicilian offshore. Landslide volume
was estimated by subtracting a pre-slide bathymetry from
the actual bathymetry. The pre-slide bathymetric model
was reconstructed by interpolating bathymetric nodes
along the scar edge.
Results
Geomorphology of the continental shelf
The continental shelf of the Gulf of Palermo occupies an
area of approximately 250 km2 and is on average 8 km
wide, narrowing to 2.5 km in front of the Mount Pellegrino
carbonate massif (Fig. 3b). The seafloor in the central part
Fig. 3 a Seismic grid and shaded relief bathymetric map of the Palermo Gulf based on data acquired during the CARG and MaGIC cruises
(2001, 2004, 2009). b Geomorphological map of the Gulf of Palermo. Bathymetric contours (in meters) every 50 m
130 Mar Geophys Res (2011) 32:127–138
123
of the shelf (between the city of Palermo and Mongerbino
Cape) is smooth and 1� steep, becoming steeper towards
the west (on average 5� steep, with maximum values of 8�)
(Fig. 3b). Along the western part of the shelf, a number of
N–S elongated highs rise 10 m from the surrounding sea-
floor ranging in depth between 60 m and 105 m (Fig. 3b).
The largest of these highs is 750 m long and 400 m wide.
The shelf-edge of the Gulf of Palermo, which is located at a
depth of 115–125 m, is indented by a number of canyons
and has a sinuous pattern (Fig. 3b). Two main canyons, the
Oreto Canyon and the Eleuterio Canyon, correspond to
the Oreto and Eleuterio rivers (Figs. 2, 3b). Offshore of the
Oreto River, seismostratigraphic data reveal the presence
of buried paleovalleys which in some cases are overlain by
sediments that dip beneath the Last Glacial Maximum
(LGM) deposits (Fig. 4).
Geomorphology of the slope region
The slope of the Gulf of Palermo is incised by a number of
submarine canyons and small scale mass failure morphol-
ogies (Figs. 2, 3b). A detailed description of the main
morphometric characters of the canyons is presented in
Table 1. The Zafferano Canyon was only partially covered
by the bathymetric survey with the result that this canyon
was not considered in the morphometric characterization of
Table 1. The canyons have minimum depths of 112 m and
maximum depths of 1,388 m, and range in length from 4.4
to 12.4 km (Fig. 5, Table 1). Downslope gradients range
from 6 to 13�, with the steepest canyons along the north-
western sector of the slope (Table 1). All the canyons
Fig. 4 P9 high-resolution sparker seismic record displaying a buried valley in front of the Oreto Canyon head. M Multiple reflector
Table 1 Main morphological features of the canyons in the Gulf of Palermo
Canyon name Shelf indenting Slope confined
Eleuterio
canyon
Oreto
canyon
Addaura
canyon
Arenella canyon Mondello
canyon
Sperone
canyon
Mongerbino
tribal valley
Total length (km) 12.1 12.2 8.5 6.75 7.1 4.9 4.4
Minimum water depth (m) 120 120 123 112 356 364 288
Maximun water depth (m) 1,380 1,330 1,329 1,115 1,388 1,200 1,160
Maximum width (m) 4,490 2,157 3,510 1,930 2,228 1,050 1,360
Maximum incision (m) 425 299 297 113 298 104 271
Slope gradient (�) 7.5 6.27 9.8 7.7 13.13 11 11.3
Left wall gradient (�) 16–18 17–18 14–23 15–20 20 20–22 14–19
Right wall gradient (�) 10–12 15–18 18–22 19–20 15–25 14–19 19–21
Fig. 5 Longitudinal bathymetric profiles of the canyons in the Gulf
of Palermo. See text for discussion
Mar Geophys Res (2011) 32:127–138 131
123
display an incised thalweg, which starts to flatten and widen
from minimum depths of 250–500 m. Most of the canyons
breach the outer shelf whereas others are confined to the
upper slope (Figs. 2, 3b and 5, Table 1). The Oreto and
Eleuterio canyons along the central sector of the Palermo
Gulf follow a straight path in a SSW–NNE direction
(Fig. 3b). The two canyons indent the outer shelf and
incise the seafloor for more than 300 m. The Oreto Canyon
displays a sinuous path reaching a depth of 300 m. Its
thalweg has a V-shaped profile and widens to a maximum
of 270 m downslope from a 750 m deep morphologic
obstacle (Fig. 6a). The configuration of the Eleuterio
Canyon is more complicated than that of the Oreto Can-
yon. Its upper sector consists of a coalescent system
composed of five main crescent shape escarpments, from
500 to 1,500 m wide, which have depths between 110 and
450 m (Fig. 6b). The crescent-shaped escarpments repre-
sent the head of the Eleuterio Canyon and coincide with an
area where faults and an antiform structure affect the
lowest part of the Quaternary succession (Fig. 7a). The
same antiform structure is at the base of a rocky mor-
phologic high mapped at a depth of 96 m to the south of
the Eleuterio Canyon head. The rocky high is probably
made up of authigenic carbonate rocks (Fig. 7b).
As in the case of the Oreto canyon, a 20 m high
obstruction at a depth of 600 m acts as a dam across the
Eleuterio canyon which, for deeper depths displays an U
shaped profile (Fig. 6b). The walls of both the Oreto and
Eleuterio canyons are from 15 to 20� steep and are carved
by gullies headed by small scars that breach the wall edges
(Fig. 6). Near the Oreto and Eleuterio Canyons, the linear
Sperone Canyon and the Mongerbino tributary valley are
confined to the slope (Fig. 2). They have a gradient of 11�and their heads are constituted by 1 km wide headscarps
350 m deep (Figs. 2, 3b).
A pockmark train is present between the Oreto and
Eleuterio Canyons, ranging in depth between 260 and 375 m
(Fig. 8). The pockmarks display a diameter ranging from
100 to 240 m and are on average 15 m deep (Figs. 8, 9).
Landslide scars, from 500 to 800 m wide and up to 20 m
high, occur below the aforementioned pockmarks (Figs. 2,
3b and 8). Seismic records across this area show the presence
of normal faults (Fig. 3b) whose N–S direction probably
coincides with the alignment of the three pockmarks.
Fig. 6 3-D shaded relief models of Oreto Canyon a and Eleuterio
Canyon b. Hs Headscarp, P Pockmark. Walls of the canyons are
carved by linear gullies headed by small scars that breach the wall
edges. The thalwegs have a V-shaped profile and widens downslope
from morphologic obstacles (label ‘‘obstruction’’ in the figure)
132 Mar Geophys Res (2011) 32:127–138
123
The western sector of the slope, adjacent to Mount
Pellegrino, presents a number of crescent-shaped escarp-
ments incised by gullies (Figs. 3b, 10). These features are
probably the headscarps of small dimension landslides
that breach the shelf-edge and form part of coalescent
systems ranging in width from 600 to 4,000 m. The
coalescent systems are the heads of three E–W oriented
straight and steep canyons: the Arenella, Addaura and
Mondello Canyons (Figs. 3b, 10). These canyons are
steeper than the Eleuterio and Oreto canyons, with slope
gradients of up to 13� for the Mondello Canyon (Table 1).
Their walls, which are 20� steep, are scoured by numer-
ous gullies with circular scarps at their heads (Fig. 10). In
contrast to the Arenella and Addaura Canyons, the
Mondello Canyon is slope confined, with its head con-
sisting of irregular shaped coalescent escarpments at a
depth between 300 and 400 m (Fig. 10).
A well preserved landslide scar, termed Priola Scar,
affects the uppermost sector of the slope, at a minimum
depth of 150 m, between the Addaura Canyon to the
North and the Arenella Canyon to the South (Figs. 10,
11). The scar, which is about 900 m wide and 100 m
high, displays a semicircular shape and a failure plan
flattening towards the toe of the detachment area, indi-
cating a rotational component in the translation mass
movement (Figs. 11, 12). The volume of the landslide has
been estimated at 24–28 9 106 m3. High resolution seis-
mics show no drapes by younger sediments, suggesting a
recent age of the failure (Fig. 12).
Discussion
Sedimentary style and processes of the Palermo
Gulf canyons
The morphologic and seismostratigraphic features of the
area suggest that a concurrence of processes contribute to
Fig. 7 a S11 high-resolution sparker seismic record displaying faults
and an antiform structure below one of the Eleuterio Canyon
headscarps. b S17 high-resolution sparker seismic record located to
the south of the Eleuterio Canyon head, displaying tectonic features
similar to those shown in Fig. 7a. The antiform structure in the record
S17 coincides with a rocky high, probably made up of authigenic
carbonatic rocks related to the escape of fluids through tectonic
lineaments. M Multiple reflector
Fig. 8 3-D shaded relief model of the pockmark field in the south-
eastern sector of the slope in the Gulf of Palermo. Note the corre-
spondence between the pockmarks and landslide scars below them
Mar Geophys Res (2011) 32:127–138 133
123
the evolution of the canyons and mass failure features that
shape the slope of the Gulf of Palermo. The axial incision
along the thalweg in most of the canyons demonstrates that
active or recent downslope sedimentary fluxes occur along
the slope (Baztan et al. 2005). Moreover, the buried valleys
in the Palermo shelf (Fig. 4) indicate a probable connection
between the Oreto River and the Oreto Canyon. Seismo-
stratigraphic data show that these valleys are older than the
LGM and that they were probably active since earlier
glacial periods. During the glacial periods the coast was
located near the shelf margin under high-energy hydrody-
namics, the fluvial sediment supply increased and valleys
channelled the sediments to the outer shelf (Field et al.
1999; Mulder et al. 2001; Hernandez-Molina et al. 2002).
Under these conditions, turbidity and mass transport pro-
cesses were more frequent along the shelf margin, con-
tributing to the evolution of the submarine canyons
(Chiocci et al. 1997; Garcia et al. 2006). The obstructions
along the Oreto and Eleuterio Canyons, which are 600 m
and 750 m deep, respectively, hamper the downslope
sedimentary fluxes and interrupt the axial incision of the
canyons. The reduction in sedimentary fluxes is evidenced
by a significant change from a narrow V shaped profile to a
broad U shaped one for depths deeper than those of the
obstacles (Fig. 6). These obstructions are probably rocky
outcrops, which are harder to erode, although further
investigation is warranted to identify their nature.
Sediment failures such as slumps and landslides corre-
spond to another prominent process that is responsible for
the evolution of the Palermo slope. The gullies along the
canyon walls display circular scars at their heads, sug-
gesting retrogressive movements (Nelson and Maldonado
1988; Klaus and Taylor 1991; Greene et al. 2002; Mulder
et al. 2006). Retrogressive mass failure events along the
continental slope facilitate the upslope propagation of
embryonic canyons towards the shelf margin (Mitchell
2005). In line with this scenario, shelf-indenting, canyons
along the western sector of the Palermo slope may
represent an evolutionary stage that is more mature than
that of the juvenile canyons such as the Mondello and
Sperone Canyons which are still confined to the slope
(Figs. 3b, 5 and 10). Once the landward migrating canyons
indent the shelf-edge, they may intercept new sediment
sources such as fluvial or along-shore transported sedi-
ments. During the evolution of the canyons, the retro-
gressive mass failures probably trigger turbidity currents,
creating incisions along the thalweg. Axial incision would
provoke undercutting, oversteepening and consequent
instability of the canyon flanks, leading to further slum-
pings during a complex scenario of concurrent top-down
Fig. 10 3-D shaded relief model of the northwestern sector of the
slope in the Gulf of Palermo. The evolution of the submarine canyons
of this sector is mostly controlled by retrogressive upslope mecha-
nisms, with the mature canyons indenting the shelf-edge (Arenella
and Addaura Canyons) and the juvenile ones still confined to the
slope (Mondello Canyon)
Fig. 9 P18 high resolution sparker seismic record across the pockmark field shown in Fig. 8, the Eleuterio headscarps and the rocky high shown
in the Fig. 7b. M Multiple reflector
134 Mar Geophys Res (2011) 32:127–138
123
and bottom-up erosional mechanisms (Twichell and Rob-
erts 1982; Farre et al. 1983; Pratson and Coakley 1996;
Baztan et al. 2005). Retrogressive failures play a major role
in the evolution of the western canyons and the other slope
confined canyons in the study area. These dynamics are due
to steep gradients of the canyons (Table 1) and to their
limited connection with fluvial inputs. By contrast, the
Oreto and Eleuterio Canyons with a gentler slope (Table 1)
and a more evident connection with shelf sedimentary
inputs (Fig. 2) appear to be more controlled by downslope
turbidity currents.
Basis for a geo-hazard assessment in the Gulf
of Palermo
Most of the morphologies described in the slope of the Gulf
of Palermo appear to be related to canyon-shaping pro-
cesses, i.e. an axial erosion due to turbidity currents and
retrogressive slope failures. In general, the results show
that the mass failure features that occur on the canyon walls
are relatively small and confined. They therefore do not
pose a significant hazard to offshore infrastructures and do
not constitute a possible threat of tsunamis along the coast
(Driscoll et al. 2000). Nonetheless, some headscarps not
confined to canyons could be potentially dangerous. Based
on the morphometric analysis, the Priola Scar is the feature
that deserves most attention. Mass failures with similar
characteristics (3.5 km from the coast, 24–28 9 106 m3,
150 m depth) may constitute a potential of tsunami inun-
dation at local scale. The landslide that occurred on the
Nice outer shelf in 1979 is comparable to the Priola scar in
terms of depth and dimensions but involved a smaller
volume of sediments. The Nice landslide caused loss of life
and considerable damage to coastal infrastructures
(Gennesseaux et al. 1980; Dan et al. 2007).
Based on the available data, the main pre-conditioning
geological factor which could have induced sediment
instability in the Gulf of Palermo is the steep gradient of
the slope. The average slope gradient of 20� registered on
the canyon walls and canyon heads may have favoured the
Fig. 12 P13 high resolution sparker seismic record across the northwestern sector of the Palermo Gulf slope. Folded and faulted deposits are
evident at the base of the Arenella Canyon head. M Multiple reflector
Fig. 11 3-D model a and bathymetric contours b of the Priola Scar. The dashed square on the 3-D model corresponds to the area covered by the
bathymetric contours
Mar Geophys Res (2011) 32:127–138 135
123
occurrence of frequent mass failure events. The steep
slopes of the canyon axes in the western sector (Table 1)
could have provoked a deep undercutting of the canyon
heads and bring about headward migration by mass failure
inside the narrow shelf. As this sector is most sensitive to
slope instabilities, it has important geo-hazard implica-
tions. The structural setting of the Gulf of Palermo could
also have contributed to the evolution of the submarine
canyons and the mass failure processes of the area. Some
evidence of this control was found in the faults and anti-
form structures mapped along the heads of the Eleuterio
and Arenella Canyons (Figs. 7a, 12), suggesting a corre-
lation between structural features, mass failures and fluid
escapes. Some of these tectonic features could have rep-
resented a preferential escape route for fluids as evidenced
by the pockmarks and by the morphologic high that coin-
cides with the apex of an antiform structure (Fig. 7b).
Pockmarks may in turn trigger mass failures as evidenced
by the headscarps observed below them. The aforemen-
tioned offshore structural features are possibly associated
with the recent tectonics mapped on-land, where N–S and
NW–SE Pleistocene faults have been mapped (Abate et al.
1978; Avellone et al. 2010) (Figs. 1, 3b).
Most of the observed mass failure features were prob-
ably generated or were more active during the glacial
periods when the coast was closer to the slope and when
the shelf margin constituted a shallow and more dynamic
setting (Burger et al. 2003; Puig et al. 2004; Garcia et al.
2006). One important aim of future research could be to
ascertain whether these features are active and whether
they pose a risk today. This would entail the identification
of the main triggering mechanisms and the evaluation of
the threat to coastal populations.
Conclusions
The application of Multi Beam and high resolution seis-
mics revealed for the first time the presence of seven
submarine canyons and mass failure features in the Gulf of
Palermo (Southern Mediterranean). The morphologies
suggest that downslope turbiditic currents and concurrent
up-slope retrogressive mass failures contribute to the
shaping of the Gulf of Palermo slope. The Oreto and
Eleuterio Canyons seem to be more controlled by turbiditic
currents whereas the canyons of the steeper western slope
are more dominated by retrogressive mass failure events.
The most prominent pre-conditioning factor in control-
ling the evolution of the canyons and in inducing the mass
failures is the steep gradient of the seafloor, especially
along the western sector of the slope. The tectonic con-
figuration of the area and punctual fluid escape processes
may have contributed to slope instability.
In the light of our findings, most of the mass failures are
small and enclosed in canyon systems, representing on the
whole a low geo-hazard. However, the northwestern sector
of the Gulf of Palermo appears to be the region that is most
prone to geo-hazard due to mass failures. Further research
such as geotechnical tests and high resolution bathymetric
surveys will yield valuable information for a reliable geo-
hazard assessment of the Gulf of Palermo.
Acknowledgments We gratefully acknowledge the Italian National
Research Projects MaGIC (Marine Geological Hazard along the
Italian Coast) funded by the Italian Civil Protection Department and
CARG (Geological Maps of Italy) funded by the Italian Geological
Survey. We thank the captains and the crews of the R/V ‘‘Thetis’’ and
R/V ‘‘Universitatis’’ for their kind assistance during the surveys. We
also acknowledge the Grup de Recerca de la Generalitat deCatalunya B-CSI (2009 SGR 146).
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