Mauro Coltelli

Geological map of Etna volcano, 1:50,000 scale

The new geological map of Etna volcano at 1:50,000 scale represents a significant progress in the geological studies of this volcano over the last 30 years, coming after Waltershausen’s map published around the mid of 19th century, the first geological map of a large active volcano, and the [Romano et alii (1979)][1] map published about a century later, both at 1:50,000 scale. Lithostratigraphy was used for mapping volcanic units and then Unconformity Bounded Units were applied to group lithostratigraphic units into synthems. In addition, lithosomes were exploited to better represent the spatial localization of different eruptive centres according to their morphology. On the whole, we identified 27 lithostratigraphic units, grouped into 8 synthems, and 9 volcanoes. In detail, effusive and explosive deposits generated by each eruption of Mongibello and, partially, Ellittico volcanoes were mapped as flow rank. This stratigraphic framework represents the best synthesis of the geological evolution of Etna volcano using the main unconformities recognized within its complex volcanic succession. In addition, we constrain the Etna volcanic succession and its lithostratigraphic units chronologically by radioisotope age determinations. On the basis of the outlined synthemic units, it was possible to divide Etna’s volcanic succession into 4 supersynthems, which correspond to 4 well-defined and spatially localized phases. The detailed reconstruction of the past eruptive activity allowed compiling the most accurate dataset in particular of the Holocene eruptions of Etna volcano, which will enable significantly improving the volcanic hazard assessment, together with petrological interpretation of erupted magmas and geophysical modelling of the volcano plumbing system. [1]: #ref-67

Structural assessment of Mount Etna volcano from Permanent Scatterers analysis

A study of the deformation pattern of Mount Etna volcano based on the results from the Permanent Scatterers (PS) technique is reported. Ground motion data provided by the interferometric synthetic aperture radar (InSAR) PS technique from 1995 to 2000 are compared and validated by GPS data. An analysis of the ascending and descending line of sight (LOS) components of ground velocities has yielded detailed ground deformation maps and cross sections. This analysis allows detection and constraint of discontinuities in the surface velocity field. LOS velocities have then been combined to calculate the vertical and horizontal (E-W) ground velocities. A wide inflation of the edifice has been detected on the western and northern flanks (over an area of about 350 km2). A seaward motion of the eastern and southern flanks has also been measured. PS data allows the geometry and kinematics of the several blocks composing the unstable flanks to be defined even in the highly urbanized areas, and their displacement rates have been measured with millimeter precision. This analysis reveals the extension of some features beyond their field evidences and defines new important features. The results of this work depict a new comprehensive kinematic model of the volcano highlighting the gravitational reorganization of the unbuttressed volcanic pile on its slippery clay basement on the southern flank, but an additional drag force due to a strong subsidence of the continental margin facing the Etna volcano is necessary to explain the PS velocity field observed on the eastern flank.

Geological Evolution of Etna Volcano

New stratigraphic and structural data obtained during recent geological surveys have allowed us to subdivide the almost continuous evolution of Etnean volcanism into four main phases. The oldest phase (Basal Tholeiitic) corresponds to a long period of dispersed fissure-type volcanism with tholeiitic affinity, from about 580 up to 260 ka. This phase represents the northward extension of the Plio-Pleistocene Hyblean volcanism to the Etnean region. The second phase (Timpe) started about 220 ka when eruptive activity was mainly concentrated on the Ionian coast along the NNW-SSE oriented Timpe fault system. In this area the occurrence of fissure-type eruptions formed a small shield volcano and the passage between tholeiitic to alkaline volcanics occurred. The third phase (Valle del Bove Centers) is marked by a main westward shift of the feeding system in the Valle del Bove (VdB) area forming some nested volcanic centers. The earliest volcanic edifices recognized are Tarderia and Rocche. Afterward the volcanism was mainly concentrated on the southwestern side of the VdB with the formation ofTrifoglietto volcano. Local shifting of the feeder caused the formation of three different volcanic centers: Giannicola, Salifizio and Cuvigghiuni. Finally, in the fourth phase (Stratovolcano) the definitive stabilization of the plumbing system led to the construction of the main stratovolcano, Ellittico, which forms the bulk of the present edifice. Four caldera-forming Plinian eruptions, occurring at about 15 ka, marked the end of Ellittico activity. During the Holocene, persistent basaltic volcanic activity formed the Mongibello volcano, whose products cover at least 85% of the Mount Etna area.

Geological evolution of a complex basaltic stratovolcano: Mount Etna, Italy

An updated geological evolution model is presented for the composite basaltic stratovolcano of Mount Etna. It was developed on the basis of the stratigraphic setting proposed in the new geological map that was constrained by 40Ar/39Ar age determinations. Unconformity bounded stratigraphy allows highlighting four main evolutionary phases of eruptive activity in the Etna region. The Basal Tholeiitic Supersynthem corresponds to a period, from about 500 to 330 ka, of scattered fissure-type eruptions occurring initially in the foredeep basin and then in a subaerial environment. From about 220 ka, an increase in the eruptive activity built a lava-shield during the Timpe Supersynthem. The central-type activity occurred at least 110 ka ago through the Valle del Bove Supersynthem. The earliest volcanic centres recognized are Tarderia, Rocche and Trifoglietto and later Monte Cerasa, Giannicola, Salifizio and Cuvigghiuni. During the Stratovolcano Supersynthem, from about 57 ka ago, the intense eruptive activity of Ellittico volcano formed a roughly 3600 m-high stratocone that expanded laterally, filling the Alcantara and Simeto paleovalleys.Finally, effusive activity of the last 15 ka built the Mongibello volcano. Its eruptive activity is mainly concentrated in three weakness zones in which the recurrent magma intrusion generates flank eruptions down to low altitude. The four main evolutionary phases may furnish constraints to future models on the origin of Etna volcano and help unravel the geodynamic puzzle of eastern Sicily.

SIR‐C/X‐SAR multifrequency multipass interferometry: A new tool for geological interpretation

Radar remote sensing is a tool of increasing importance in the study of volcanic sites. Synthetic aperture radar (SAR) is a high-resolution imaging tool used to survey areas which are not practical or safe to be directly inspected. With the introduction of the across-track SAR interferometry (IFSAR) technique, digital elevation models (DEM) can be produced. The usefulness of such interferometric products depends on the ability to extract information that can be used for geological interpretation. We analyzed the shuttle imaging radar C (SIR-C)/X-SAR multifrequency multipass interferometry mission over Mount Etna, Sicily, and we performed a supervised geological interpretation of the coherence maps and a fractal-based analysis of the IFSAR DEMs. The first permits us to recognize different volcanic terrain and to distinguish between vegetated and unvegetated areas, while the second allows us to validate the IFSAR DEMs and to detect large-scale geological features. This latter analysis, performed over the photogrammetric DEM, enabled us to recognize artifacts caused by digitizing and resampling. Obviously, IFSAR DEMs are not affected by these problems. As a consequence, IFSAR products are a valuable aid in geological interpretation.

The volcano-tectonic map of Etna volcano, 1:100.000 scale: an integrated approach based on a morphotectonic analysisfrom high-resolution DEM constrained by geologic, active faulting and seismotectonic data

A new volcano-tectonic map of Etna volcano has been compiled through a morphotectonic analysis performed with detailed field mapping, high-resolution DEM and orthoimages, constrained by seismotectonic data. In this study, we present a homogeneous mapping of the volcano-tectonic and tectonic elements on the whole volcano, consistent with the updated knowledge on the geology and active tectonics observed in historical times. Details of the tectonic features occurring in the lower-middle part of the volcanic edifice, namely the more densely urbanized areas, are described; volcanic elements such as eruptive fissures, caldera and flank collapse rims affecting the upper sectors, are also reported. All the volcanic landforms of Etna edifice have been generated by constructive and destructive volcanic processes largely during the last 15 ka activity of Mongibello volcano. DEM-derived images (e.g. slope and aspect maps) were produced and interpreted in order to identify faultrelated surface features based on an explicit list of well-known elements of tectonic geomorphology. Subsequently, the morphotectonic mapping has been compared with field data on geologic marker offsets, as well as evidence of surface faulting, including coseismic displacements and creeping of historical and recent events. This combined approach has enabled classifying each element reported in the map as (i) exposed faults, (ii) buried faults and (iii) hidden faults. The analysis of slip-rates confirms the exceptional dynamics of the Pernicana fault, which is characterised by an almost constant slip-rate of 20-36 mm/a over the last 1000 years, while the Timpe fault zone and the structural system in the southern flank accommodate a relevant amount of deformation with slip-rates reported to range of ca. 2-4 mm/a. Finally, a seismotectonic model summarises the information regarding seismic hazard, with reference to the additional, potentially severe effects induced by surface faulting.

40Ar/39Ar isotopic dating of Etna volcanic succession

Since the 1970s, about 50 radio-isotopic ages have been determined on Etna volcanics using different techniques: Th-U and K/Ar.Unfortunately, these ages cannot be readily used to constrain the new stratigraphic setting of the volcano, because of the uncertainty in sample locations or, sometimes, the large errors affecting the calculated ages. For this reason a program of radio-isotopic dating applying the 40Ar/39Ar incremental heating technique to date the groundmass of basaltic samples has been carried out from 2002.Forty samples (22 of which are of new publication) were collected from key outcrops on Etna volcano, selected on the basis of their stratigraphic position, while one sample was collected from the Hyblean plateau volcanics. We have obtained reliable results from all volcanics analysed from 542 ka up to 10 ka with the MSWDs (Mean Square of Weighted Deviates) ranging from 0.03 up to 1.7 excluding IS sample (MSWD = 6.28). These new results allow us to: i) assign an age to 19 of the 25 lithostratigraphic units defined in the new geological map of Etna volcano; ii) clarify the uncertain stratigraphic position of isolated volcanic units; iii) constraint the temporal hiatus that matches the main unconformities; iv) outline the lapse of time between the end of the Hyblean volcanism and the beginning of eruptive activity in the Etna region.

The Landslide Sequence Induced by the 2002 Eruption at Stromboli Volcano

The complex sequence of large-scale tsunamogenic instability phenomena occurred on the subaerial and submarine NW flank of the Stromboli Volcano soon after the beginning of the December 2002 eruption is reconstructed and its relationship with volcanic activity is evidenced. After a brief description of slope morphology and stratigraphy, geometry and kinematics of the landslides are described. Finally, instability mechanisms that controlled the subaerial and submarine slope failures are proposed with reference to the different geotechnical, hydraulic, and loading/strain conditions that characterized the different stages of the slope evolution.

The morphological evolution of the Sciara del Fuoco since 1868: reconstructing the effusive activity at Stromboli volcano

The morphological evolution of the Sciara del Fuoco, Stromboli, is described from a time series dataset formed by Digital Elevation Models and orthophotos derived by digitising historical contour maps compiled in 1868 and 1937 and by processing data from aerial surveys carried out between 1954 and 2009. All maps were co-registered in the same reference system and used to build a quantitative reconstruction of the morphological changes of the Sciara del Fuoco slope. The changes mainly relate to the emplacement of many lava flows and their successive erosion. A comparative quantitative analysis yields estimates of areas and volumes of the lava fields formed on the sub-aerial part of the Sciara del Fuoco during a number of effusive events between 1937 and 2001, some of them never assessed before. The results of the analysis constrain the interpretation of the evolution and the magnitude of the recent effusive activity at the Stromboli volcano. Despite some uncertainties due to widely spaced observation periods, the results integrate all available topographic knowledge and contribute to an understanding of the main characteristics of the recent effusive eruptive styles at Stromboli volcano.

Last 100 Ka Tephrostratigraphic Record of Mount Etna

The tephro- and chrono-stratigraphic synthesis of Etna pyroclastic deposits of the last 100 ka is presented here. Deposits correlation over the whole volcanic edifice allows the reconstruction of a continuous pyroclastic succession from about 100 ka to the Present. Tephra layers are composed of scoria or pumice lapilli and ash, representing pyroclastic fall or flow deposits interbedded with continental volcanogenic sedimentary deposits. They are grouped into five stratigraphic units corresponding to main periods of explosive activity. On the basis of the tephro- and chrono-stratigraphic data they are: (A) about 100 ka basaltic strombolian activity; (B) 80-100 ka benmoreitic plinian eruption that ends the activity of the Trifoglietto volcano; (C) 16-80 ka strombolian to subplinian eruptions, basaltic to mugearitic in composition, of the post-Trifoglietto (Giannicola, Salifizio and Cuvigghiuni and Ellittico) volcanoes; (D) 15-15.5 ka benmoreitic-trachitic caldera-forming plinian eruptions that end the activity of the Ellittico volcano; and (E) the last 12 ka basaltic subplinian eruptions and the 122 BC plinian eruption of the Mongibello volcano. The tephrostratigraphic reconstruction indicates that the explosive activity presented different features during the history of Etna. Eruptive styles cover a range from strombolian to plinian, producing some marker beds that have a great importance in the new geological reconstruction of Etna. High volatile content of Etna magmas seems to be the key factor for the origin of this strong explosive activity. The characterization of Etna explosive activity has given this kind of activity a new relevance and important implications for the volcanic hazard assessment at Etna, a volcano commonly considered, before these studies, just effusive.