Activity of mount Etna, 1977–1983: Volcanic phenomena and accompanying seismic tremor

A period of exceptional eruptive activity for both size and frequency of lateral eruptions, and violence of paroxysms at the summit craters characterized Etna from 1977 to 1983.The complex fissure eruption of 1971 and the eccentric eruption of 1974 on the W flank appear to be precursors of the present activity, which began in July 1977 with the change in style of summit eruptions from moderate persistent activity to intermittent paroxysms. The NE Crater produced a score of such unusual eruptions up to March 1978, lasting a few days or even a few hours with powerful lava fountaining and flows up to 7 km long with high effusion rates. Other solely explosive paroxysms occurred in April 1980 in the Chasm (Central Crater) and later at the SE Crater. A return to a period of gentle persistent activity (May–August 1980) at the latter vent was interrupted by the recommencement of violent explosive and effusive events at the NE Crater in September 1980 and February 1981.Particularly remarkable lateral (flank) eruptions occurred in April–June 1978 (fracturing of the SE slope from 3000 to 2600 m altitude), August 1978 (SE, ENE, 3000–2300 m), November 1978 (SE, 3000–1650 m), August 1979 (SE, E, NE, 3000–1600 m), March 1981 (NNW, 2600–1120 m) and March–August 1983 (S, 2700–2260 m). The first four of these eruptions were preceded and accompanied by violent lava fountaining at the SE Crater. All were accompanied and/or followed by phreatic explosions, principally from the Bocca Nuova (or W Central Crater). The flow emitted on 4th August 1979 from the eastern flank reached next to the village of Fornazzo in half a day. That of 17 March 1981 — the most destructive — cut all communications (roads and railways) round the northern foot of the mountain in the 14 hours following its appearance. It was in places 800 m wide, and in less than 5 days, 18 × 10⁶ m³ of lava had been emitted, covering 6 km² of largely agricultural land. From 28th March to 6th August 1983, the slow but sustained emission of lava gradually covered and destroyed several tourist installations between 2300 and 1100 m altitude.Each of these eruptive paroxysms was marked by a substantial increase in the trace amplitude of harmonic seismic tremor, the intensity of which being not directly proportional to the observed activity. It is likely that turbulence caused by the rising of magma in the main conduits had an important effect in the energy of the tremor: this is considerably reduced after the initial paroxysmal phase (e.g. in 1983), yet the lava effusion may continue.Tremor energy attains relatively high levels from 1 to 5 months before eruptions. This may be caused by the recharging of the system of dykes and fissures, leading up to an eruptive event after a variable period. Several distinct periods of recharging may precede one eruption (there were three before the 1983 eruption).In the few days preceding the start of some of the eruptions (Aug. 1979, Sep. 1980, Feb. and Mar. 1981), a rapid diminution in the amplitude of tremor occurred. This may be associated with changes in the stress field caused by the opening of new fractures or the closing/opening of pre-existing ones.

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Resume L'Etna a connu, de 1977 à 1983, une période d'activité exceptionnelle, tant par la fréquence et l'extension des fracturations latérales de l'édifice que par la violence et la répétition des paroxysmes aux cratères centraux.L'éruption multifissurale de 1971 et l'éruption excentrique de 1974 sur le flanc Ouest apparaissent comme les prodromes de l'activité actuelle. Celle-ci a débuté en juillet 1977 par l'exacerbation de l'activité sommitale qui, de modérée persistante, est devenue paroxysmique et intermittente. Jusqu'en mars 1978, le Cratère NE a eu ainsi une vingtaine d'éruptions tout à fait inusitées, ne durant que quelques jours ou même quelques heures, avec puissantes fontaines de lave et coulées rapides atteignant jusqu'à 5 km de long. D'autres paroxysmes uniquement explosifs ont eu lieu en avril 1980 au Cratère Central, puis au Cratère SE. Un début d'activité persistante (mai-août 1980) dans cette dernière bouche a été interrompu par la reprise de violentes manifestations explosivo-effusives au Cratère NE en septembre 1980 et février 1981.Les éruptions latérales surtout ont été remarquables: en avril-juin 1978 (fracturation du versant SE, de 3000 à 2600 m d'altitude), août 1978 (SE, ENE, 3000–2300 m), novembre 1978 (SE, 3000–1650 m), août 1979 (SE, E, NE, 3000–1600 m), mars 1981 (NNW, 2600–1120 m), mars-août 1983 (S, 2700–2260 m). Les 4 premières de ces éruptions ont été précédées et accompagnées de violentes fontaines de lave au Cratère SE. Toutes ont été accompagnées ou suivies d'explosions phréatiques, principalement à la bouche Ouest du Cratère Central. La coulée du 4 août 1979 sur le flanc oriental est descendue en une demi-journée près du village de Fornazzo. Celle du 17 mars 1981 — la plus désastreuse — a, dans les 14 h qui ont suivi son apparition, coupé toutes les communications terrestres au pied Nord de l'Etna, sur un front par endroits large de 800 m: en moins de 5 jours, 18 × 10⁶ m³ de lave ont été émis, recouvrant 6 km² de terres en grande partie cultivables. Du 28 mars au 8 août 1983, les laves s'épanchant de façon tranquille, mais à un rythme soutenu, ont lentement enseveli plusieurs propriétés et implantations touristiques du versant Sud, entre 2300 et 1100 m d'altitude.Chacun de ces paroxysmes éruptifs se signale par des augmentations considérables de l'amplitude du tremor séismique, dont l'intensité n'est cependant pas directement liée à l'importance des phénomènes observés. Il est probable que la turbulence due à la montée du magma dans les conduits principaux influe notablement sur l'énergie du tremor: de fait, celui-ci est très réduit après la phase paroxysmique initiale (par exemple 1983), bien que l'effusion de lave persiste.Avant les éruptions, l'énergie du tremor atteint des niveaux relativement élévés pendant des intervalles de temps qui durent de 1 à 5 mois. Ce phénomène peut résulter d'un mécanisme de recharge du système de fractures et de dykes conduisant, à plus ou moins brève échéance, à l'événement éruptif. Plusieurs périodes de recharge peuvent se succéder avant une même éruption (3 avant celle de 1983).Dans les quelques jours qui précèdent certains paroxysmes (août 1979, sept. 1980, févr. et mars 1981), on constate une rapide diminution de l'amplitude du tremor, qui peut être associée à des variations du champ de contrainte déterminant, localement, la genèse de fractures nouvelles ou la fermeture/ouverture de fractures pré-existantes.

     

Marble-hosted ruby deposits from Central and Southeast Asia: Towards a new genetic model

Marble-hosted ruby deposits represent the most important source of colored gemstones from Central and South East Asia. These deposits are located in the Himalayan mountain belt which developed during Tertiary collision of the Indian plate northward into the Eurasian plate. They are spatially related to granitoid intrusions and are contained in platform carbonates series that underwent high-grade metamorphism. All occurrences are located close to major tectonic features formed during Himalayan orogenesis, directly in suture zones in the Himalayas, or in shear zones that guided extrusion of the Indochina block after the collision in South East Asia. Ar–Ar dating of micas syngenetic with ruby and U–Pb dating of zircon included in ruby gives evidence that these deposits formed during Himalayan orogenesis, and the ages document the extensional tectonics that were active, from Afghanistan to Vietnam, between the Oligocene and the Pliocene.The petrography shows that ruby-bearing marbles formed in the amphibolite facies (T = 610 to 790 °C and P ~ 6 kbar). A fluid inclusion study defines the conditions of gem ruby formation during the retrograde metamorphic path (620 < T < 670 °C and 2.6 < P < 3.3 kbar) for the deposits of Jegdalek, Hunza and northern Vietnam.Whole rock analyses of non-ruby-bearing marbles indicate that they contain enough aluminum and chromiferous elements to produce all the ruby crystals that they contain. In addition, (C, O)-isotopic analyses of carbonates from the marbles lead to the conclusion that the marbles acted as a metamorphic closed fluid system that were not infiltrated by externally-derived fluids. The carbon isotopic composition of graphite in marbles reveals that it is of organic origin and that it exchanged C-isotopes with the carbonates during metamorphism. Moreover, the O-isotopic composition of ruby was buffered by metamorphic CO₂ released during devolatilisation of marble and the H-isotopic composition of mica is consistent with a metamorphic origin for water in equilibrium with the micas. The (C, O, H)-isotopic compositions of minerals associated with marble-hosted ruby are all in agreement with the hypothesis, drawn from the unusual chemistry of CO₂–H₂S–COS–S₈–AlO(OH)-bearing fluids contained in fluid inclusions, that gem ruby formed at P ~ 3 kbar and 620 < T < 670 °C, during thermal reduction of evaporite by organic matter, at high temperature-medium pressure metamorphism of platform carbonates during the Tertiary India–Asia collision. The carbonates were enriched in Al- and chromiferous-bearing detrital minerals, such as clay minerals that were deposited on the platform with the carbonates, and in organic matter. Ruby formed during the retrograde metamorphic path, mainly by destabilization of muscovite or spinel. The metamorphic fluid system was rich in CO₂ released from devolatilisation of carbonates, and in fluorine, chlorine and boron released by molten salts (NaCl, KCl, CaSO₄). Evaporites are key to explaining the formation of these deposits. Molten salts mobilized in situ Al and metal transition elements contained in marbles, leading to crystallization of ruby.     

Morphostructure of the Egyptian Continental Margin: Insights from Swath Bathymetry Surveys

In the Eastern Mediterranean, offshore Egypt, the Nile continental margin is characterized by a large deep water turbiditic system known as the Nile Deep Sea Fan. This post-Miocene terrigenous construction covers an approximately 10 km-thick sedimentary pile, including 1–3 km of Messinian salt layers. Systematically collected swath bathymetric data proved to be the most powerful tool to discover, describe and study many sea floor features of this sedimentary construction which reflects competition between active tectonic, sedimentary, and geochemical processes. Gravity tectonics, triggered by underlying mobile salt layers, construction of channel-levee systems, the passage of turbidite flows, sedimentary slope failures at various scales, massive mud expulsions and fluid seepages are all interfering to shape the Nile Deep Sea Fan seabed.     

Marine spatial planning in the high seas

Although high seas resources are being exploited, reciprocal legal obligations to protect its environment have not been met. Marine spatial planning (MSP) is clearly a practical way forward, particularly for the high seas, where non-spatial monitoring is difficult, and where data gaps obstruct conventional management approaches. To ensure the effective application of MSP in the high seas, however, some institutional reforms are necessary. This paper outlines the main hurdles, summarizes existing high seas spatial protections, presents an example of a high seas marine protected area that resulted through MSP, identifies three institutional priorities, and suggests three immediate steps.     

Beyond nationalism: Three visions of the European Union and their implications for the linguistic regime of its institutions

The linguistic diversity in the European Union is generally viewed as an essential component of the European identity, but the linguistic regime of the EU institutions (with eleven official and working languages) is not undisputed. In addition, the upcoming enlargements will complicate greatly the continuation of the present practices as new Member States bring new official languages. As a result, the debate about possible reforms is likely to be boosted by the necessity to prepare EU institutions for further enlargment. The present regime of institutional multilingualism is criticised from different angles, resulting in three options for the future. In this paper the linguistic regime of EU institutions is discussed in relation to general ideas about the nature of this supranational political system. Supranationalism is treated here as a program to supersede nationalism. Three variants are distinguished: pacified nationalism, neo-nationalism and post-nationalism. The paper examines how these different visions of Europe shed different lights on the issue of multilingualism (in terms of communication, identity and power) and its institutionalisation in the linguistic regime of the core instituions of the European Union. Although the three models are compatible with several arrangements, they support or oppose them for different reasons. Besides, they differ regarding the significance of the linguistic regime of the EU institutions for the whole polity and their ability to steer linguistic practices.     

Grid-group cultural theory: an introduction

This article offers an introduction to grid-group cultural theory (also known as grid-group analysis, Cultural Theory or theory of socio-cultural viability), an approach that has been developed over the past thirty years in the work of the British anthropologists Mary Douglas and Michael Thompson, the American political scientist Aaron Wildavsky, and many others. This assessment begins with a presentation of the main claims of the theory, distinguishing two characteristic breads of grid-group cultural theory, in the one it is conceived as a heuristic device, in the other it is seen as a full explanatory theory. This brief is followed by a discussion of the typology generated by the theory. This includes a presentation of the two dimensions of sociality it posits, the cultural map they produce, as well as the four (or five) cultural types derived from them and their designations. The article proceeds with a discussion of key issues including the incorporation of other typologies (such as the one developed to analyse myths of nature), the relations between cultures or rationalities and several methodological issues. Finally the article introduces the contributions to this special issue of the GeoJournal. This revised version was published online in August 2006 with corrections to the Cover Date.     

Behaviour of colloidal trace metals (Cu, Pb and Cd) in estuarine waters: An approach using frontal ultrafiltration (UF) and stripping chronopotentiometric methods (SCP)

The frontal cascade ultrafiltration (UF) technique in conjunction with stripping chronopotentiometry (SCP) has been evaluated for determining the colloidal distribution of Cu, Pb and Cd in estuarine waters. Metallic concentrations in seven size fractions (0.45 μm–0.22 μm; 0.22 μm–300 kDa; 300–50 kDa; 50–30 kDa; 30–10 kDa; 10–5 kDa; <5 kDa) were determined with the aim to investigate their changes along the salinity gradient of the Penzé system (NW France). These data, completed by analysis of the total dissolved metals at 10 stations over the whole freshwater–seawater mixing zone, provided some insights in the removal and addition processes that affect Cu, Pb and Cd in estuaries.