View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Scientific Open-access Literature Archive and Repository GEOLOGICA CARPATHICA, FEBRUARY 2011, 62, 1, xx—yy doi: 10.2478/v10096-011-0005-z Gravity instabilities in the Dohrn Canyon (Bay of Naples, Southern Tyrrhenian Sea): potential wave and run-up (tsunami) reconstruction from a fossil submarine landslide VINCENZO DI FIORE, GEMMA AIELLO* and BRUNO D’ARGENIO Institute for Marine Coastal Environment (IAMC), National Research Council of Italy (CNR), Calata Porta di Massa, Porto di Napoli, 80133 Napoli, Italy; *[email protected] (Manuscript received June 30, 2010; accepted in revised form December 6, 2010) Abstract: We discuss a mathematical model for wave and run-up generated submarine landslides in the canyons of the Bay of Naples (Magnaghi-Dohrn canyon system). The morpho-bathymetry and submarine gravity instabilities of such incisions have been investigated through the interpretation of a high resolution DEM. The canyons are located in a sector of the bay where there is a variable interaction of volcanic activity (Phlegrean Fields and Ischia and Procida Islands) with sedimentary processes due to the Sarno-Sebeto rivers. At present the Naples canyon-system is inactive, as is shown by the Holocene sedimentary drapes deposited during the present sea-level highstand, but gravity instabilities occurred in the recent past at the canyons’ heads. In particular the Dohrn Canyon is characterized by a double regressive head, while the Magnaghi Canyon shows a trilobate head, formed by the junction of three main tributary channels and coincident with the retreat of the shelf break around the 140 m isobath. The results of a simulation of failures in the above source areas show that the amplitude of wave run-up, expressed in terms of the sea floor depth percentage, may range up to 2.5 % of the water depth at the sea bottom. Key words: Bay of Naples, tsunamigenic potential, run-up landslide, numerical modelling. Introduction on the study of tsunamis generated by landslides from Ischia’s slopes. The catastrophic collapse that formed the large scar in The aim of this paper is to study potential wave and run-up the southern flank of Ischia (the Ischia Debris Avalanche of events caused by submarine landslides located in the can- Chiocci & de Alteriis 2006) may be considered as the upper yons of the Bay of Naples. limit for tsunamigenic failures in the slopes of Ischia, even Tsunami waves, often caused by gravitative failures, may though the duplication of such an event does not appear prob- be generated by earthquakes and less frequently by volcanic able at the moment. In this study we selected an area of the eruptions. In the Bay of Naples all the above trigger factors Dohrn Canyon showing evidence of paleo-landslides and we are present. As a consequence, the continental slope off the applied a model to evaluate the wave run-up generated by an bay represents an appropriate natural laboratory to study estimated flow, using a recent theoretical model (Lynett & Liu geological events potentially leading to submarine slides 2002; Di Fiore et al. 2008). with their tsunamigenic potential. The geological setting of the bay has been studied in detail in the framework of research programmes for submarine geo- General setting of the area logical cartography (Aiello et al. 2001; Bruno et al. 2003; D’Argenio et al. 2004).Article In this gulf the continental slope and inThe eastern Proof margin of the Tyrrhenian Sea is characterized by the outer shelf are deeply incised by two submarine canyons of a number of basins formed during the latest Neogene-Quater- kilometric extent, namely the Dohrn and Magnaghi Canyons, nary across the structural boundary between the Apennine fold representing the drainage system of this active volcanic area and thrust belt and the Tyrrhenian back-arc extensional area during the Late Quaternary. Detailed mapping of the outer (Fig. 1). These basins, including the Bay of Naples and the shelf and slope morphology contributed to the understanding Bay of Salerno (Fig. 1) evolved as a consequence of the large- of erosional and depositional processes related to continental scale orogen-parallel extension and related transtensional tec- slope settings and allowed their geological interpretation to be tonics that accompanied the anti-clockwise rotation of the proposed (Aiello et al. 2001; D’Argenio et al. 2004). Apennine belt and lithospheric stretching in the central Several studies about tsunamis have recently been carried Tyrrhenian Basin (Sacchi et al. 1994; Ferranti et al. 1996; out in the Bay of Naples. Landslide-generated tsunamis in the D’Argenio et al. 2004). offshore of Ischia Island have been featured by Zaniboni et al. As a consequence, the Campania segment of the peri- (2007) in the framework of a project on the volcanic hazard Tyrrhenian structural belt displays the characteristics of a pas- and risk assessment of the island of Ischia, by the National sive continental margin, where Quaternary orogen-parallel Institute for Geophysics and Volcanology and the Italian extension caused the formation of half-graben systems (Gulf Department for Civil Protection. The above authors focussed of Gaeta, Bay of Naples, Bay of Salerno and intervening www.geologicacarpathica.sk 2 DI FIORE, AIELLO and D’ARGENIO Fig. 1. Tectonic sketch map of western Campania Apennines (modified after D’Argenio et al. 2004). 1 – Shallow- water carbonate and deep basinal units (Mesozoic); 2 – Piggy-back siliciclastic units (Tertiary); 3 – Pyroclastic depos- its and lavas (Quaternary); 4 – Conti- nental and marine deposits (Quaternary); 5 – Normal fault; 6 – Detachment faults (barbs indicate downthrown side). structural highs (e.g. Sorrento Peninsula, Mt Massico), acoustic basement of the coastal basins and are composed either trending perpendicularly to the main axis of the Apennine of terrigenous-shaly basinal sequences or of thick platform and thrust belt (Mariani & Prato 1988; Sacchi et al. 1994; Milia basinal Mesozoic-Cenozoic carbonates (Fig. 1). Extensional & Torrente 1999; Aiello et al. 2000). tectonics accompanying the uplift of the southern Apennines Off the Campania coasts the peri-Tyrrhenian basins often begin in the Early Pliocene and continue up to the Middle—Late form the seaward extension of the coastal plains, whose for- Pleistocene, playing a major role in controlling the present-day mation was controlled by extensional tectonics during the physiography of the Campania Region. Indeed, Quaternary ma- Plio-Quaternary (Mariani & Prato 1988; Brancaccio et al. rine and continental sediments of the Campania coastal plains 1991). Their tectono-sedimentary evolution is connected reach a thickness of up to 3000 m in the Volturno Plain and of with the Neogene evolution of the Apenninic chain (Royden 1500 m in the Sele Plain (Ortolani & Torre 1981). et al. 1987; Patacca & Scandone 1989). In particular, the de- NW-SE, NE-SW and E trending post-orogenic structures formational history of the peri-Tyrrhenian basins is charac- (mainly extensional faults) have been previously recognized terized by alternating compressional and extensional tectonic under the sea near the Campania Region (Bartole et al. 1983). phases during Plio-Quaternary times (Bartole 1984; Argnani While the Apenninic (NW-SE) trending structures character- & Trincardi 1990; Agate et al. 1993; Sacchi et al. 1994). ize the continental slope areas between the Pontine Islands and The Neogene evolution of the south-eastern peri-Tyrrhe- the Cilento Promontory, the Anti-Apenninic (NE-SW) ones nian basins was controlled by large-scale extensional tecton- often occur under the sea near the Bay of Salerno and the ics, responsible for the thinning of the western sectors of the structural high of the Sorrento Peninsula. southern Apenninic chain and dating back to the Late Mio- In turn, the Quaternary extension along the Campania seg- cene. Thinning due to extension was not homogeneously ment of the Southern Apennine—Eastern Tyrrhenian hinge distributed along the overthrust belt, but rather localized in zone caused the onset of intense volcanism. It was responsible discrete hyper-extensionArticle domains (Ferranti et al. 1996), infor the creation Proof of both single large volcanoes (Roccamonfina where the thrust pile was locally reduced to about one half of and Somma-Vesuvius – Principe et al. 1987: fig. 1) and vol- its original thickness. canic complexes (Ischia, Procida and Phlegrean Fields – Modes of extension along the peri-Tyrrhenian basins are Rosi & Sbrana 1987: fig. 1). In the Phlegrean area a thermo- often characterized by listric normal faults and associated metamorphic basement about 1500 m deep has been inferred antithetic faults, which generated SW-NE trending half-gra- (Rosi & Sbrana 1987), whereas in the Volturno Plain the “Vil- ben systems along the Tyrrhenian Basin-southern Apennines la-Literno” 1 and “Parete” 1 wells drilled into thick basaltic system. Most of them extend landward to the E-NE. This and andesitic lavas (Ortolani & Aprile 1978). causes a typical coastal landscape made of alternating trans- versal mountain ridges and intervening coastal plains. In the Campania Region Quaternary basin fillings overlie Morpho-bathymetry and sea bottom instability of submerged “internal” (western) tectonic structures of the Apen- the Naples bay canyons ninic chain, resulting from the seawards extension of the tecton- ic units cropping out in the coastal belt of the southern An extensive, high resolution bathymetric survey of the Apennines (D’Argenio et al. 1973: fig. 1). These units form the continental shelf/slope system of Campania, Southern Italy GRAVITY INSTABILITIES IN CANYON, POTENTIAL WAVE AND TSUNAMI RECONSTRUCTION (BAY OF NAPLES) 3 has recently been carried out. The relative bathymetric data sea-level eustatic fall, inducing a seaward migration of the riv- were acquired during the years 1997 and 2002, using Multi- er systems of the Late Pleistocene and the formation of the beam systems with an average vertical resolution of ≤0.25 % valleys, coupled with a fault block rotation, responsible for the water depth and a position accuracy of ≤10 m.