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: loiacono@cmima.csic.es

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

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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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