Geodetic techniques applied to the study of the Etna volcano area (Italy)

Volcanic behaviour of Mt. Etna is due to the complex interaction between both the local and the regional stress field involving the eastern Sicily. Eruptions could trigger (be triggered?) during crust extension and/or compression, which are strictly linked with the dynamics of the lower mantle. In this study, very long baseline interferometry (VLBI) space geodesy technique has been used in order to study Etna volcano's activity by means of the crustal deformations between Noto and Matera (located on the African and the Eurasian Plates, respectively). By analysing VLBI data, we obtained the behaviour of the baseline which crosses the Etnean area, from 1990 December to 2003 March, representing the time variations of the distance between the two geodetic stations; the linear trend of the baseline shows a general increasing, pointing out an extension of the crust between them. A detailed analysis of the Noto-Matera baseline allows the identification of three parts of the VLBI curve in the considered period. In the first part of the curve (from 20/12/90 to 09/02/94), VLBI data are rather poor and therefore no reliable consideration about correlation between crust movements and volcanic and seismicity activity has been made. In the second part of the curve (from 09/02/94 to 04/09/00), VLBI data are more frequent and show slightly fluctuations in the distance. Increasing in the extension and compression were observed in the central and in the final part of this period. In the third period (from 04/09/00 to 25/03/03), VLBI data are very sparse even if the time series was quite long; therefore, to fill gaps in the information, we analysed global positioning system (GPS) data. GPS technique performs continuous observations, and we were able to highlight both extensions and compressions in detail. Comparisons between the trend of Noto-Matera baseline length variations, volcanic activity and seismicity in the Etna area show the complexity of the development over time and space of the phenomenology determined by a deep cause which can be traced, in our opinion, to the interaction between the asthenospheric mantle, deep crust and surface crust. Therefore, we state that crustal distension and compression are determined by the lower pulsating mantle

Radionuclide measurements as tool for geophysical studies on Mt. Etna Volcano (Sicily)

Radionuclide measurements as tool for geophysical studies on Mt. Etna Volcano (Sicily

A multidisciplinary study of the volcanoclastic deposit named "Chiancone", inland and offshore, in the frame of the evolution of volcanism in the Etna area

International audience► In the CH's pyroclasts there are various lithological facies which were generated 50-40 Ky B.P., in particular violent geodynamic manifestations of the volcano (various opening episodes of the Valle del Bove, strong hydromagmatic, strombolian explosions, etc.). ► In various phases, the CH's volcaniclasts have occupied some Grabens of the pyroclastic body C, which is in southern zone of the area studied (La Delfa et al., 2007). In the northern zone, a tectonic depression as deep as 400 m and oriented WNW-ESE (Fig. 9:3), accommodated most of the pyroclastic flows. The North face of this ditch, towards Giarre-Riposto seems to be made up of non-volcanic sedimentary rocks, while the South face is formed by the pyroclasts from the geological body C, as the offshore multibeam surveys show (Fig. 11). ► The CH's pyroclasts poured into the sea reaching a maximum depth of 100 m b.s.l. (surveys by the "Istituto Idrografico della Marina", 1993), near Torre Archirafi, overcoming two morpho-tectonic steps: the sedimentary one North of Torre Archirafi (Fig. 9:3; Fig. 10,E) and the pyroclastic one (body C), South of Torre Archirafi, near Praiola Piccola (Fig. 4). In accordance with our results, Loddo et al. (1989) using deep dipole measurements found a rise in the non-eruptive substratum in the same area along the coast. ► Considering the presence of morpho-structural steps near the coast and the different depth of the base of the CH to the west (about 300 m, below the sea level) and to the east, off the coast line (at about 100 m below the sea level) of these steps, the possibility that the impact of the mass of the detritus, although quite modest, falling into the Ionian Sea may have caused a tsunami wave (Pareschi et al., 2006) big enough to affect the central-eastern Mediterranean about 8 000 years B.P. is excluded, in our opinion. Indeed, as is known, the CH's pyroclasts were deposited in various successive episodes, over quite a long time frame (40-50 ky) and considering the particular morphology of the conductive substratum in the area under study, they mostly filled the various existing depressions to the west of these steps, interacting only a bit with the waters of the Ionian Sea

Volcanism and mantle–crust evolution: The Etna case

International audienceMount Etna is located in a particular region of convergence of African and Eurasian plates where intense post-collisional tectonics caused considerable uplift. However we present arguments supporting the hypothesis that volcanism and associated seismic activity would result from a local mantle uprise leading to a “horst”, probably linked to a deep-rooted hot spot. It ensued deformation and fracturing of the overlying crust with emission of aphyric tholeiitic basalts directly from their mantle source, and subsequent development of a “deep reservoir” (or complex of intrusions) at the top of a mantle diapir near 30 km depth. This is advocated by the appearance of porphyritic alkaline lavas whose mineral equilibria and differentiation processes are consistent with an 8–10 kbar pressure, and by the development of central volcanoes. The horst itself appears to have begun in the SW sector of the present volcanic area. Its uplift was greater westward, as seen from the trend of the terraces along the Simeto river, and became later obvious toward the SE. These differential movements produced fractures and faults which are to day evident in the southern area of Mt Etna. The growth of the horst then proceeded in a NE direction, following the regional tectonic lines and with a greater intensity along the side facing SE, crossed by the regional NNW–SSE line (Aeolian–Maltese escarpment). The seismicity and ground deformation registered over the last twenty years support the proposed model. Earthquakes are unfrequent in the lower southern and western areas of the volcano, whereas they are numerous and stronger to the north-east, in the summit area above 1600 m a.s.l., and in the eastern sector along the NW–SE faults and fractures. Finally, a digital elevation model recently published reveals the existence of two tectonic domains. The first one is associated with the horst and contains prevalently NE–SW oriented faults, whereas the second is mainly linked to regional tectonics with NNW–SSE and NW–SE faults and fractures

New archeomagnetic and Ra-226-Th-230 dating of recent lavas for the Geological map of Etna volcano

This work deals with the dating of Mount Etna lava flows and eruptive fissure deposits to the last four millennia following field investigations and stratigraphic data (BRANCA et alii, 2011a). We have studied 24 of these volcanic products, including 301 large samples, through high precision archeomagnetic dating checked by 226Ra-230Th radiochronology, thus providing additional material to the previous paper by TANGUY et alii (2007). In most cases our results allow attributing ages to the historical period, although two flows are shown to be prehistoric. For the historic lavas, archeoma - gnetic ages can be defined within decades, except for three of them that erupted during a time span (Greco-Roman epoch) when the geomagnetic field underwent little variation. Although 60% of these volcanics exhibit ages comprised between 700 AD and 1850, only one (1285) is mentioned by contemporary written accounts. We conclude that i) historical documents alone are insufficient to reconstruct a coherent sequence of eruptions, and ii) a multidisciplinary approach is necessary to obtain a comprehensive eruptive history of such a very active volcano, useful for both scientific and civil protection purposes, even for such a geologically recent period as that of the last 10 or 20 centuries. Thanks to these new archeomagnetic and 226Ra-230Th data coupled with stratigraphic data, a comprehensive volcanic history of the still-outcropping Mount Etna volcanics is now available for the last 2,400 years. KEY WORDS: Etna volcano, archeomagnetic dating, 226Ra- 230Th dating, stratigraphy, historical account

Mount Etna eruptions of the last 2,750 years: revised chronology and location through archeomagnetic and 226Ra-230Th dating

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