Plinian eruptions and their impact on human settlements: stratigraphy of the 79 AD Vesuvius fall deposits and detailed study of their downwind and substrate-induced variations inside the archaeological excavations of Pompeii and Stabiae (southern Italy)

<p>Plinian eruptions are highly energetic events that release cubic kilometres of magma in the form of pyroclastic material (pumice, lithic clasts and ash). These products tend to accumulate near the vent with considerable thickness. The rapid burial of the territory around the eruptive centre makes these eruptions extremely dangerous. For this purpose, the renowned 79 AD Vesuvius eruption, which destroyed the ancient cities of Pompeii and Stabiae (where Pliny the Elder founds his death) located respectively 10 and 15 km from the vent, was studied in detailed. The recent excavations carried out in collaboration with the Archaeological Park of Pompeii, both in Pompeii and in the Stabian villas, have shown the complete sequence of products of the 79 AD eruption that destroyed and covered these Roman cities. The discovery of thick sequences of reworked material accumulated during previous excavations, testifies for the presence of underground tunnels dug for the Royal House of Bourbon. Fall products of the 79 AD eruptive sequence, accumulated during the main Plinian phase and the successive sustained column phases, were studied in detail to investigate their sedimentological characteristics and how these were influenced by anthropic structures. Results from field investigation show that in both archaeological sites, fall deposits consist of white and grey pumice lapilli in the lower part of the eruptive sequence (units A and B), and of thin, lithic-rich layers interstratified to ash products emplaced by pyroclastic currents, in the highest part of the pyroclastic deposit (units D, G1, G3, I). A new thin lithic-rich layer (X2) has been observed near the top of the sequence at Stabiae. The internal structure of the Plinian pumice lapilli deposit appears weakly stratified in open areas, while it is strongly stratified near steep roofs (e.g., impluvium areas), where the deposit thickens. The observed stratification is confirmed by a significant variation of sedimentological parameters with the stratigraphic height (e.g., median ranging from -3.5 to -0.1), possibly related to fluctuations in the eruptive parameters. Locally, rolling of pyroclastic clasts on sloped roofs produced a well-stratified deposit with laterally discontinuous layers and rounded clasts. Several roofing-tiles, either intact or in fragments, were recovered at various stratigraphic heights in the pumice lapilli deposit both at Pompeii and Stabiae.  These tiles testify for the progressive collapse of the roofs under the increasing load of the falling lapilli clasts.</p>

Constraints on the pre-eruption thermal and fO2 conditions in the magma reservoir of Ciomadul (SE Carpathians, Romania) based on Fe-Ti oxide geochemistry

<p>Ciomadul is the southernmost eruptive centre of the post-collisional Călimani-Gurghiu-Harghita andesitic-dacitic volcanic chain (SE Carpathians, Romania) and represents the latest manifestation of the Neogene to Quaternary volcanism in the Carpathian-Pannonian Region. Ciomadul consists of older, peripheral shoshonitic to dacitic lava domes formed episodically between 1 Ma and 300 ka and a voluminous, central volcanic complex developed within the last 200 ka. Although several lines of evidence (based on petrology, geophysics and gas monitoring) suggest a long-lived magmatic plumbing system holding a potentially active magma storage (“PAMS” volcano) beneath Ciomadul, the pre-eruptive conditions of the upper crustal magma reservoir (including temperature, oxygen fugacity and TiO<sub>2</sub> activity) are not completely explored so far. In this study 23 rock samples, representing the whole volcanic activity of Ciomadul in time, were involved. Fe-Ti oxide (magnetite-ilmenite) grains were selected from magnetic heavy minerals, but only a few of the samples contained both magnetite and ilmenite crystals. Equilibrium between Ti-magnetite and ilmenite was tested by their chemical composition (Mg/Mn ratios).</p><p>Various geothermobarometer calibrations, including Andersen and Lindsley (1985, 1988) as well as Ghiorso and Evans (2008), were applied to calculate temperature and oxygen fugacity from Fe-Ti oxide compositions. Our results show that, in case of dacitic pyroclastic rocks, temperature values gained by the method of Ghiorso and Evans are significantly lower (640–780 °C) than those obtained by the geothermometers of Andersen and Lindsley (1985, 1988), showing 750–830 and 710–790°C temperatures, respectively. On the other hand, andesitic lava dome rocks of Dealul Mare show higher, 800–900 °C temperature according to all of these methods. The obtained temperature was compared with amphibole-plagioclase thermometry results and this shows a better agreement with the values yielded by the Andersen and Lindsley (1985) Fe-Ti oxide thermometry, particularly for the pumice samples.</p><p>In case of oxygen fugacity, the Ghiorso and Evans (2008) and Andersen and Lindsley (1985) methods showed fairly similar values (fO<sub>2</sub>=0.9–1.8) whereas the Andersen and Lindsley (1988) calculations gave higher oxygen fugacity (fO<sub>2</sub>=1.1–2.5). Nevertheless, these results, irrespective the applied calculation methods, suggest relatively oxidized conditions (ΔNNO>1) what is comparable with many other andesitic to dacitic volcanic systems (e.g. Mount St. Helens, Mount Unzen, Santorini). Values of TiO<sub>2</sub> activity was calculated and obtained a range between 0.76 and 0.98 what is consistent with the common presence of titanite.</p><p> </p><p>This study was financed by NKFIH K135179 project.</p><p> </p><p>Andersen, D.J. & Lindsley, D.H. (1985). EOS Transactions of the American Geophysical Union, 66, 416.</p><p>Andersen, D.J. & Lindsley, D.H. (1988). Amer Miner 73:714–726.</p><p>Ghiorso, M.S. & Evans, B.W. (2008). Amer J Sci 308:957–1039.</p>

Carbonic nanostructures in subsurface rocks: problem review Part II. Graphene, carbonic nanotubes, nanofibers

The paper reviews the publications on the search and exploration of carbonic nanotubes and other nanocarbonic structures in subsurface rocks. It is shown that the graphenes and carbonic nanotubes (CNT) exist in the composition of various magmatic and sedimentary rocks. They are formed in the graphite globules of volcanic rocks, as well as in the sediments, where the pressure, the particles of metallic catalysts, the tension stresses and time factors in million years compensate the absence of high temperatures. Experimental laboratory modeling of natural processes has been carried out and the reality of formation of carbonic nanostructures during the pyrolysis of volcanic gases on the lava catalysts, mechanical activation and processing of amorphous carbon or bituminous coal shown. Principal possibility of realization of technology of CNT mass production via pyrolysis of hydrocarbon crude material in the presence of different catalytically-active natural minerals has been reviewed and proven. The analysis of the aspects following the activity of mud volcanoes shows that there are all suppositions for the formation of carbonic nanostructures: the pressure bump of deep rocks out of the hot eruptive centre, methane as carbonic crude, catalytically-active breccias containing transition metals and their oxides, the process of methane burning in the medium poor of oxygen. However, it is not yet absolutely clear. As a working hypothesis we propose a model of formation of these structures due to the mud volcanism activity in the reactions of methane flow, the catalysts in which natural minerals exist. In such processes as a result of intensive methane flow, there occur negative pressure values and cavitation effects in the presence of which local temperature and pressure increase efficient for formation of adamantine and nanosize carbonic structures take place. In case if this mechanism is real, the studies point to a perspective of obtaining valuable products in conditions of natural geological processes. There are no messages or publications yet on the exploration of carbonic nanostructures in the rocks of mud volcanoes.

Post 3.9 Ma fault activity within the West Antarctic rift system: onshore evidence from Gandalf Ridge, Mount Morning eruptive centre, southern Victoria Land, Antarctica

A hawaiite dyke dated at 3.88 ± 0.05 Ma from the Mount Morning eruptive centre intrudes a diamictite deposit at Gandalf Ridge in the southern Ross Sea. The dyke has been dextrally offset up to 6 m horizontally by faults interpreted as the onshore continuation of the West Antarctic rift system (WARS) fault array. Felsic dykes emplaced during the Miocene are also present at Gandalf Ridge. The offset of the Miocene dykes is equivalent to the offset on the hawaiite dyke, suggesting that at this locality movement on faults within WARS has been restricted to a period more recent than c. 3.88 Ma. Over this period the minimum average rate of movement on these faults within WARS is 0.0015 mm yr-1.

Reassessment of the historical seismic activity with major impact on S. Miguel Island (Azores)

On account of its tectonic setting, both seismic and volcanic events are frequent in the Azores archipelago. During the historical period earthquakes and seismic swarms of tectonic and/or volcanic origin have struck S. Miguel Island causing a significant number of casualties and severe damages. The information present in historical records made possible a new macroseismic analysis of these major events using the European Macroseismic Scale-1998 (EMS-98). Among the strongest earthquakes of tectonic origin that affected S. Miguel Island, six events were selected for this study. The isoseismal maps drawn for these events enabled the identification of areas characterized by anomalous values of seismic intensity, either positive or negative, to constrain epicentre locations and to identify some new seismogenic areas. Regarding seismic activity associated with volcanic phenomena six cases were also selected. For each of the studied cases cumulative intensity values were assessed for each locality. The distribution of local intensity values shows that the effects are not homogeneous within a certain distance from the eruptive centre, the area of major impacts relates with the eruptive style and damages equivalent to high intensities may occur in Furnas and Sete Cidades calderas. Combining all the historical macroseismic data, a maximum intensity map was produced for S. Miguel Island.