Istituto di Geologia Ambientale e Geoingegneria, CNR. (**) Dipartimento di Scienze della .... Instituto Geológico y Minero de España, IGME. Tres Cantos 28760,.
GS5 - Sedimentary and Biological Processes
TS5.3 Mediterranean Sea as natural laboratory for active processes at seabed (fluid, mass waiting, seismicity)
CONVENERS
Jean Mascle (Geoazur, Observatoire de la Côte d’ Azur, Nice, France) Silvia Ceramicola (OGS Trieste)
Rend. Online Soc. Geol. It., Vol. 21 (2012), pp. 946-947,1 fig. © Società Geologica Italiana, Roma 2012
Recent mass-wasting processes and related geohazard at Stromboli and Vulcano (Italy) DANIELE CASALBORE (*), CLAUDIA ROMAGNOLI (**), ALESSANDRO BOSMAN (*), FRANCESCO LATINO CHIOCCI (°)
Key words: submarine landslide, multibeam, La Fossa caldera, Sciara del Fuoco, Aeolian Islands.
INTRODUZIONE Stromboli and Vulcano islands are two active volcanoes located in the Aeolian Arc (Southern Tyrrhenian sea). Their submarine portions account for about 98% and 80% of the whole
extent of volcanic edifice, respectively (BOSMAN et alii, 2009; ROMAGNOLI et alii, 2012). The flanks of these volcanic edifices are very steep and covered by volcaniclastic sediments due to a large spectrum of mass-wasting processes, ranging from largescale sector collapses to small landslides (CASALBORE et alii, 2011; ROMAGNOLI et alii, 2012). The geohazard related to these processes is very high, as demonstrated by the occurrence of a medium-scale tsunamigenic landslide on 30 December 2002 at Stromboli (Fig 1a; CHIOCCI et alii., 2008).
Fig. 1 – Residual map (scale bar units are in meters) obtained as difference between pre- and post-“2002 Stromboli landslide” draped over the shaded relief of Sciara del Fuoco slope at Stromboli volcano; the red dashed line indicates the limit of the subaerial landslides; three pre- and post-landslide cross-section of 2002 landslide scar are also shown (modified from Casalbore et alii, 2012). b) La Fossa Caldera emerged and submerged sectors, with the indication of the 1988 tsunamigenic landslide and erosive gullies (white arrows, modified from Romagnoli et alii, 2012); the location maps of the Fig. 1a and b are reported in the inset
_________________________ (*) Istituto di Geologia Ambientale e Geoingegneria, CNR (**) Dipartimento di Scienze della Terra e Geologico-Ambientali, Università Alma Mater di Bologna (o) Dipartimento di Scienze della Terra, Università Sapienza di Roma This reseach has been partially funded by MaGIC (Marine Geohazard along the Italian Coast) project
The aim of this work is to depict recent mass-wasting and erosive processes that affect the submarine flank of these volcanic edifices, with particular reference to the areas offshore two very active sectors, i.e. the Sciara del Fuoco at Stromboli (Fig. 1a) and La Fossa caldera at Vulcano, where a small tsunamigenic landslide occurred in April 1988 (Fig. 1b; TINTI et alii, 1999). This task has been realized through the integration of multibeam, long-range side scan sonar and seismic data collected in the last 20 years from IGAG-CNR of Rome and the Universities of Rome (Sapienza) and Bologna. 946
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REFERENCES BOSMAN, A., CHIOCCI, F.L., ROMAGNOLI, C., (2009) - Morphostructural setting of Stromboli volcano, revealed by highresolution bathymetry and backscatter data of its submarine portions. Bullettin of Volcanology, 71, 1007-1019. CASALBORE, D., ROMAGNOLI, C., BOSMAN, A., CHIOCCI, F.L. (2011) - Potential tsunamigenic landslides at Stromboli Volcano (Italy): Insights from marine DEM analysis. Geomorphology, 126, 42-50. CASALBORE D., BOSMAN A., CHIOCCI F.L. (2012) - Study of recent small-scale landslides in geologically active marine areas through repeated multibeam surveys: examples from the Southern Italy. In: Y. Yamada, et alii (Eds.) - Submarine
Mass Movement and Their Consequences, "Advances in Natural and Technological Hazards Research" Series, 31, 573-582. Doi: 10.1007/978-94-007-2162-3_51. CHIOCCI, F.L., ROMAGNOLI, C., TOMMASI, P., BOSMAN, A., (2008) - The Stromboli 2002 tsunamigenic submarine slide: characteristics and possible failure mechanisms. Journal of Geophysical Research, 113, B10102. ROMAGNOLI C., CASALBORE D., CHIOCCI F.L (2012) - La Fossa Caldera breaching and submarine erosion (Vulcano Island, Italy). Marine Geology, 303-306, 87-98. TINTI, S., BORTOLUCCI, E., ARMIGLIATO, A., (1999) - Numerical simulation of the landslide induced tsunami of 1988 on Vulcano Island, Italy. Bullettin of Volcanology, 61, 121-137.
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Size Distribution of Submarine Landslides along the Gioia Basin. Tyrrhenian Sea (Italy) D. CASAS (*), F. CHIOCCI, D. CASALBORE (**) & G. ERCILLA (°)
Key words: Geohazard, Gioia Basin, Statistical distribution, Submarine slides .
INTRODUCTION The magnitude-frequency relationship of sedimentary instabilities is essential for a proper hazard assessment at regional scale. The distribution of sedimentary instabilities, their recurrence of certain sizes, and triggering mechanisms are variables for determining their potential hazard. Regional inventories that incorporate these variables represent the first step to establish the probability of triggering a sedimentary instability, with certain dimensions, and during a period of time. For subaerial landslides, it has been suggested the cumulative number-area and cumulative number-volume relationships can be described by inverse power-law distributions based on the dimensions of the failure scar, slide deposits or headwall length (GUZZETTI et alii, 2002; DUSSAUGE et alii, 2003, Guthrie and Evans, 2004, MALAMUD et alii, 2004). In the marine environment, those relationships have resulted successful for a few studied cases (TEN BRINK et alii, 2006; MICALLEF et alii, 2008). In most of those studies the inverse power law distribution only explained a truncated portion of mapped inventories, and the size distribution appeared to fit a log-normal distribution. In these cases, normal distribution was often attributed to an undersampling of landslides with a given size range. The distribution based on the inverse power law results from a self-organized critical behavior. This implies that from equivalent initial conditions, a series of events resulting from additive processes can be generated. This is explained, in terms of instability processes, by the fact that the metastable region on which the instability is propagated once initiated, can grow by coalescence of smaller regions. By contrast a log-normal distribution implies that the metastable region is destabilized instantly. Then, the final size of a landslide depends on the characteristics of the trigger (e.g. magnitude) and adjusts for local variations such as slope, strength etc. _________________________ (*) Instituto Geológico y Minero de España, IGME. Tres Cantos 28760, Madrid (**)Universita de Roma “La Spienza”. Pz. Aldo Moro 5. 00185 Roma. (°)ICM-CSIC. P. Marítim de la Barceloneta 08003. Barcelona. This work has been developed in the framework of the MAGIC project and the “José Castillejo” program (JC010-134).
The work here presented is based on the analysis of geological and geomorphological characteristics of a large area of Gioia Basin, in the Tyrrhenian Sea (Fig. 1), in order to generate interpretive maps that allow the identification and characterization and spatial distribution of sedimentary instabilities.
GEOLOGICAL FRAMEWORK The Gioia Basin is an intra-slope basin located between the NE margin of Sicily and S Calabria, and is divided into two subbasins (N and S) by the Acquarone structural high. In the southern margin of Calabria, this structural high separates also another intra-slope basin called Palmi (Fig. 1). The continental shelf is practically absent along the margin of Calabria, although locally it is about 5 km wide along the northeast coast of Sicily, facing the structural high Acquarone. The N Gioia Basin (NGB), limited laterally by structural highs, shows as a main morphological feature the Gioia-Mesima canyon/channel system (GMS). This system is characterized by a double head defining the canyons Gioia and Mesima that evolve to channels with the same name beyond the foot of slope (COLANTONI et alii, 1992). The GMS system is tributary of Stromboli valley (CASALBORE, 2009, 2011).
METHODOLOGY The development of this work has been done on the basis of bathymetric data acquired in the framework of the MAGIC project (Map of Geohazard-related features of the seafloor of Italy) which aims to make the mapping of geological hazards along the Italian margins. The methodology for this study is based on the characterization and mapping of each of the instabilities as well as the definition of their headwalls. This has allowed calculating the position and length of the scars, their area, and the volume of sediment mobilized. The volume of sediment has been calculated using Digital Elevation Model and GIS tools. The protocol is based on 4 key steps: 1) definition of the boundaries of the headwalls, 2) export of those limits (x, y, z) for generation a surface simulating the initial seafloor conditions, 3) extraction of the surface that defines the post-slide area, and 4) calculation of volume by
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86° CONGRESSO SOCIETÀ GEOLOGICA ITALIANA 18-20 SETTEMBRE 2012, ARCAVACATA DI RENDE (CS)
Fig. 1 – Bathymetry of the study area (dashed line). (B) Detail of the instabilities mapped on the margins of Gioia and Mesima channels.
superimposing the two surfaces. The minimum size of an identifiable instability is a function of resolution bathymetric. This resolution is higher in shallow areas. For this reason the instabilities defined by a perimeter of less than 0.10 km have been dismissed.
the smallest one is located at 19 m depth, and has a scar of 50 m long. The headwall area covers 171 m2 and involves a sediment volume of 200 m3.
DISCUSSION AND CONCLUSIONS RESULTS
We have studied the geology and geomorphology characteristics of an area of about 3350 km2 in the Gioia Basin which has allowed the identification and characterization of 420 landslides. These landslides affect an area over 87 km2 and are responsible for the mobilization of about 1.5 km3 of sediment. The 59% of instabilities are located in the heads and sidewalls of the canyons and channels, like MSG and Acquarone (Fig. 1). The remaining 41% are located in the open slope and the walls of structural highs bounding the the Gioia Basin. The largest landslide occurs in the slope at 1500 m water depth and is defined by a scar of 7 km long. The headwall area covers 11 km2 and involves a sediment volume of 0.4 km3. By contrast,
Bibliographic compilation about the Mediterranean Sea published by CAMERLENGHI et alii, 2010, indicates that the mapped instabilities in this sea are relatively small in size with respect others, for example from N Atlantic. That inventory identifies a total of 532 sedimentary instabilities. Most of them (419) have a size between 10 and 103 km2 and only 77 display sizes less than 10 km2. However that inventory lacks of observations of smaller sedimentary instabilities. By contrast, the inventory carried out in this work represents an opportunity to improve the statistical significance of the frequency distribution at different spatial scales. This is because it incorporates a large number of measurements in small landslides (
