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CONTRIBUTION OF DISTAL ASH DEPOSITS TO THE KNOWLEDGE OF EXPLOSIVE ACTIVITY OF ITALIAN VOLCANOES INSIGHTS FOR HAZARD ZONATION.
Abstract
In addition to the destruction of the sites close to the volcanoes, the accumulation of volcanic ash in distal zones can cause serious damages but the evaluation of the related hazard is not fully addressed in present day mitigation plans. The dispersion study joined with the physical and geochemical characterization, of distal pyroclastics deposits produced by explosive eruption of Italian volcanoes during late Quaternary was the focus of this PhD project. The distal deposits were investigated through the tephrostratigraphic study of three lacustrine cores from Lake Shkodra and Lake Ohrid (Albania), and one marine core from the northern Ionian Sea. Seventeen tephra layers were correlated with explosive eruptions of A.D. 472, Avellino (3.9 cal. ka BP) from Somma-Vesuvius, Monte Pilato (A.D.1200), Gabellotto-Fiumebianco (8.6 cal ka BP) and Monte Guardia (22 ka BP) from Lipari Island, FL (3.4 cal. ka BP) from Mount Etna, Astroni (4.2 cal. ka BP), Agnano Monte Spina (4.5 cal. ka BP), Agnano Pomici Principali (12.3 cal. ka BP), SMP1-Y3 (31 ka) and Campanian Ignimbrite-Y5 (39 ka) from Phlegrean Fields, X6 (107 ka) from Campanian, P11 tephra layer (131 ka) from Pantelleria Island. Five other tephra layers have the Mercato deposit composition from Somma-Vesuvius. This suggests the occurrence of interplinian activity between the eruptions of Mercato (8.9 cal ka BP) and Avellino (3.9 cal ka BP). All the data were collated into a GIS and integrated with literature data. This data-base implemented in a GIS environment allows a significant improvement of the ash dispersal and represents an useful tool for the improvement of volcanic hazard mitigation in Central Mediterranean area.
... Significantly, over the last decades , marine tephra studies in this area have allowed to improve the reconstruction of the explosive activity of the Mediterranean volcanoes (e.g. Keller et al., 1978; Paterne et al., 1986 Paterne et al., , 1988 Paterne et al., , 1990 Paterne et al., , 2008 Siani et al., 2004; Lowe et al., 2007; Margari et al., 2007; Turney et al., 2008; Bourne et al., 2010; Caron, 2010; Caron et al., 2010). In addition to their interest for volcanology, the identification of tephra layers on land and/or in the marine sediments has supplied a significant stratigraphic support to paleoclimatic and paleoceanographic investigations in this basin, improving chronology and correlation of marine, continental, and cryospheric records at ultra-regional scale (e.g. ...
... Paterne et al., 1986; Siani et al., 2001; Caron et al., 2010; Lane et al., 2010; Sulpizio et al., 2010a Sulpizio et al., , 2010b Zanchetta et al., 2011). The Tyrrhenian, Adriatic and Ionian seas are the best studied basins of the Mediterranean because of the prevailing seasonal wind directions that mainly dispersed ash particles to the east and southeast, at least for the last 200 ka (Keller et al., 1978; Paterne et al., 1990 Paterne et al., , 2008 Siani et al., 2004; Bourne et al., 2010; Caron, 2010 ). However, the inspection of the location of the published cores shows an evident lack of data in the north part of the Ionian Sea. ...
... Tephra layers are then defined by the relative abundance of volcanic glass shards with respect to detrital crystals and lithics in the same fraction after counting of at least 400 particles under a stereo-microscope. Volcanic glass occurs throughout the core, and forms a background at about 4% of abundance for the 323 counted samples (Fig. 2; Appendix 1; Caron, 2010). Therefore, we considered only abundance peaks larger than two times the background as representative of tephra deposition and selected for laboratory analyses. ...
A detailed tephrostratigraphic study supported by stable isotope (δ18O) analyses and AMS 14C dating was carried out on a high sedimentation rate deep-sea core recovered in the northern Ionian Sea. Eight tephra layers were recognised, all originated from explosive eruptions of southern Italian volcanoes. These tephra layers are correlated with terrestrial proximal counterparts and with both marine and lacustrine tephra already known in the central Mediterranean area. The oldest tephra (dated at ca. 19.4 ka cal BP) is tentatively correlated to the Monte Guardia eruption from Lipari Island. Two other rhyolitic tephra layers were correlated with the explosive volcanic activity of Lipari Island: Gabellotto-Fiumebianco/E-1 (8.3 ka cal BP) located close to the interruption of Sapropel S1 deposit, and Monte Pilato (ca. AD 1335) in the uppermost part of the core. The Na-phonolitic composition of the other five recognised tephra layers indicates the Somma-Vesuvius as the source. The composition is quite homogeneous among the five tephra layers, and fits that of the Mercato proximal deposits. Beyond the striking chemical similarity with the Mercato eruption, these tephra layers span over ca. 2000 years, preventing correlation with the single well known Plinian eruption of the Somma-Vesuvius. Therefore, at least two of these tephra layers were assigned to an interplinian activity of the Somma-Vesuvius between the eruptions of Mercato and Avellino, even though these eruptions remains poorly constrained in the proximal area. By contrast, the most prominent tephra layer (2 mm white tephra visible at naked eyes) was found within the S1a Sapropel interval. Despite the possible complication for the presence of similar eruption with different ages we argue that Mercato is probably a very good marker for the onset of sapropelic condition in the Ionian Sea and can be used for land-sea correlations for this important climatic event. More in general, these data allow a significant update of the knowledge of the volcanic ash dispersal from Lipari and Somma-Vesuvius volcanoes.
... Much more information about distal ash deposits can be gained from the collection and collation of tephrostratigraphic data elaborated in sedimentary records for the Central Mediterranean area, which serve as archives of distal volcanic ash (Fig. 1). Tephrostratigraphic studies in the Central Mediterranean have been carried out at different times over the last 30 years (Keller et al. 1978; Paterne et al. 1988; Siani et al. 2004; Wulf et al. 2004; Lowe et al. 2007; Caron 2010; Sulpizio et al. 2010; Zanchetta et al. 2011). This large data set has not been well exploited from a volcanological point of view, and only recently has attention been given to the use of tephrostratigraphy for characterising distal ash deposits from past explosive eruptions of Italian volcanoes (Sulpizio et al. 2008) and for constraining numerical simulations of past events (Costa et al. 2012). ...
Volcanic ash produced during explosive eruptions can have very severe impacts on modern technological societies. Here, we use reconstructed patterns of fine ash dispersal recorded in terrestrial and marine geological archives to assess volcanic ash hazards. The ash-dispersal maps from nine Holocene explosive eruptions of Italian volcanoes have been used to construct frequency maps of distal ash deposition over a wide area, which encompasses central and southern Italy, the Adriatic and Tyrrhenian seas and the Balkans. The maps are presented as two cumulative-thickness isopach maps, one for nine eruptions from different volcanoes and one for six eruptions from Somma-Vesuvius. These maps represent the first use of distal ash layers to construct volcanic hazard maps, and the proposed methodology is easily applicable to other volcanic areas worldwide.
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