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Volcanoes produce probably the most spectacular geological phenomena on Earth. Any of their eruptions can have a strong consequence on the surrounding environment, often captured in great detail in the sedimentary records of volcanically active regions. In addition, flank landslides and background erosive processes affecting volcanic sequences release volcanic particles that circulate within sedimentary environments up to billions of years after their generation. Therefore, exploring volcanically influenced sedimentary environments is an exciting and challenging scientific exercise requiring insights across multiple geological disciplines, drawing upon an increasing varied range of expertise and analytical approaches from across the geoscientific community. This book aims to provide an updated collection of works that illustrate the state-of-the-art in this topic, and to define the future directions of the geological sciences in utilizing and interpreting sedimentary records of volcanism.

The genesis of particles and their transport mechanisms are the two fundamental factors driving the accumulation of sediments associated with volcanism or derived from volcanic sources. These factors are therefore the most important criteria on which to base a useful classification of sediments in such environments. However, the relative significance of the nature of particles v. the transporting mechanism forming a deposit varies in existing terminological schemes: those schemes applied where volcanological contextual information is available tend to give precedence to the transportation process; whereas sedimentological schemes examining ancient deposits tend to focus principally on the nature of particles. Here, we provide an outline of the challenges in classifying volcanically derived sediments and put forward a scheme that aims to bridge current terminological differences and accommodate variable levels of uncertainty. This work defines three endmembers ( primary volcaniclastic , secondary volcaniclastic , volcanic epiclastic ) that correspond to (a) deposits whose particles are produced, transported and emplaced directly by volcanic mechanisms; (b) deposits whose particles are produced directly by volcanic events but transported and accumulated by non-volcanic mechanisms, either in continuum with the events or after interim storage; (c) deposits whose particles are produced by weathering/erosion of volcanic terrains and transportation of derived material by non-volcanic mechanisms. When the complex combination of genetic and transportation processes accumulating volcaniclastic sequences is not clear, but a strong relationship between an eruptive event and the studied volcaniclastic deposit can still be demonstrated, a further category ( volcanogenic ) has been introduced.

Evacuation planning and management represents a key aspect of volcanic crises because it can increase people protection as well as minimize the potential impact on the economy, properties, and infrastructure of the affected area. Assessment of evacuation scenarios that consider human and economic impact is best done in a pre-disaster context as it helps authorities develop evacuation plans and make informed decisions outside the highly stressful time period that characterizes crises. We present an agent-based simulation tool that assesses the effectiveness of different evacuation scenarios using Vulcano island (Italy) as a case study. Simulation results show that the overall time needed to evacuate people should be analysed together with the percentage of people evacuated as a function of time and that a simultaneous evacuation on Vulcano is more efficient than a staged evacuation. We also present a model to assess the economic impact of evacuation as a function of evacuation duration and starting period that reveals that an evacuation of Vulcano would cause significant economic impact to the tourism industry if lasting more than 3 months (in case it was initiated at the beginning of the visitor season) to 1 year (in case it was initiated at the end of the visitor season).

The youngest (last 1500 years) volcanic eruptions of Lipari, within the Aeolian Archipelago, produced the prominent pumice cone of Monte Pilato and the obsidian lava flows of Rocche Rosse and Forgia Vecchia, concentrated in the north-eastern sector of the island as well as highly dispersed white-coloured, fine-grained tephra layers of rhyolitic composition in terrestrial and marine settings on the regional scale. Here we describe in detail the stratigraphy of pyroclastic successions and lava flows erupted by different vents - Monte Pilato, Forgia Vecchia, Lami, and Rocche Rosse - combining field observations, sedimentological characteristics of the tephra deposits, and major and trace element compositions of the volcanic glass. All the pyroclastic materials consist of aphyric pumice lapilli and ash with a largely homogeneous rhyolitic composition. The Monte Pilato and Forgia Vecchia deposits primarily consist of highly vesicular pumice fragments and subordinate obsidian clasts, whilst Rocche Rosse and Lami are characterized by moderately vesicular juvenile fragments with a more significant fraction of obsidian. The Lami tephra also contains peculiar pumice clasts with a fibrous texture and breadcrust bombs. Stratigraphic relationships, and paleomagnetic and 14C ages of the lava and pyroclastic deposits are combined with the archaeological information and historical reports, enabling us to provide an accurate chrono-stratigraphic framework for the youngest eruptions of Lipari. Following the 8th century CE eruption of Monte Pilato, which produced a pumice cone and a obsidian lava flow, activity resumed in the second half of 13th century CE with the explosive eruption of Forgia Vecchia that culminated in the emission of a bilobate obsidian lava flow. This eruption was shortly followed by the explosive eruptions of Lami and Rocche Rosse, the latter concluded with the emission of the widely renowned obsidian lava flow. By integrating stratigraphy and geochemistry of tephra deposits with a new chronological scheme, our work facilitates the refinement of proximal-to-distal correlation of Lipari's rhyolitic tephra in continental marine environments of the central Mediterranean area in the last 1500 years. A fine-grained, rhyolitic ash found on Stromboli (~40 km NE from Lipari) has an origin from the Monte Pilato and thus, constrains tephra dispersion towards the NE. Very similar ash beds dispersed southwards and interlayered within the near-source deposits of La Fossa, Vulcano island (~10 km from Lipari) exhibit features that are consistent with the younger activities of the Rocche Rosse eruption. A possible link between previously identified rhyolitic ash layers identified in marine cores of the Ionian Sea and the Forgia Vecchia eruption are postulated, although the age and textural characteristics of these distal tephra are not univocal in indicating a correlation to either Monte Pilato or Forgia Vecchia.

During continental rifting, strain and magmatism are believed to localize to narrow magmatic segments, while the rift margin is progressively abandoned. We integrate volcanological, geochemical, petrological and seismic data from the Ma’Alalta volcanic field (MVF) near the western margin of Afar, to show that the MVF is an active magmatic segment. Magmatism in MVF initiated with lava flows and large-volume, caldera-forming ignimbrites from a central edifice. However, the most recent magmatic activity shifted towards mafic lava fields, cinder cones and obsidian-rich silicic domes erupted from vents aligned NNW-SSE, defining a ~ 35-km-long magmatic segment. Along the same area, a NNW-SSE alignment of earthquakes was recorded by two local seismic networks (2005–2009 and 2011–2013). The geochemistry of the mafic rocks is similar to those of nearby axial volcanoes. Inferred magma storage depth from mineral geobarometry shows that a shallow, silicic chamber existed at ~ 5-km depth below the stratovolcano, while a stacked plumbing system with at least three magma storage levels between 9 and 24 km depth fed the recent basalts. We interpret the wide set of observations from the MVF as evidence that the area is an active magmatic segment, showing that localised axial extension can be heavily offset towards the rift margin.

Lahars are rapid flows composed of water and volcaniclastic sediments, which have the potential to impact residential buildings and critical infrastructure as well as to disrupt critical services, especially in absence of a hazard-based land-use planning. Their destructive power is mostly associated with their velocity (related to flow rheology and surrounding topography) and to their ability to bury buildings and structures (related to the deposit thickness). The distance reached by lahars depends on their volume, on sediments/water ratio, as well as on the overall characteristics of the path where they propagate. Here we present a novel strategy for the assessment of risk associated with lahar inundation related both to flow velocity and deposit thickness using Vulcano island (Italy) as a case study. First, a range of hazard scenarios has been identified that are related to the mobilization by intense rain events of tephra fallout deposited on the slopes of the La Fossa cone by a future Vulcanian eruption. Second, a numerical model has been used to identify the potential lahar impact areas on the northern sector of Vulcano, where both residential and touristic facilities are present. In this specific case we have used the Smoothed Particle Hydrodynamic (SPH) model that provides information on both flow velocity and deposit thickness. Finally, exposure and vulnerability surveys were carried out in order to compile risk maps for both lahar-flow velocity and final lahar-deposit thickness. Our analyses show the importance of carrying out accurate and detailed risk assessments exploring a variety of initial conditions in order to best quantify the potential damage and identify suitable mitigation strategies.

I convegni sull’ambiente di Villa Bertelli a Forte dei Marmi, si pongono l’obiettivo di fare dialogare scienza, rappresentanti del territorio e mondo della scuola per analizzare le sfide ambientali del comprensorio Apuo-Versiliese. Il fine ultimo di questi eventi è quello di mettere a disposizione degli organi di governo e gestionali del territorio e professionisti, elementi conoscitivi rigorosi ed oggettivi necessari a indentificare i problemi e le possibili soluzioni e a guidare le strategie di medio e lungo periodo [...].

Growth of rift segments and development of crustal magmatic systems in continental rifts remain debated issues. We integrate volcanological, geochemical, petrological and seismic data from the Ma’alalta stratovolcano near the western rift margin of Afar to show that active magmatic rifting occurs there. Growth of Ma’alalta started around 0.55 ± 0.05 Ma (Barberi et al. 1972) with the age of the youngest flows unknown. Ma’alalta produced lava flows but also large-volume, caldera-forming ignimbrites, as well as silicic intracaldera domes. The products are mainly trachytic and some are slightly peralkaline. The most recent magmatic activity of Ma’alalta consists of mafic lava fields, scoria cones and peralkaline obsidianaceous silicic domes produced along the ~40 km long magmatic segment and erupted from several vents aligned NNW-SSE rather than from central volcanic activity. Local seismicity (2005-2009 and 2011-2013) also shows a NNW-SSE-trending alignment of earthquakes with good correlation to where the recent magmatic products were erupted. The geochemical features of the mafic rocks (e.g., Ba/La, Rb/Ta and Zr/Ta) as well as the petrogenesis of the recent NNW-SSE-trending silicic domes are similar to the nearby on-rift Dabbahu and Durrie volcanoes. Inferred magma storage depth from mineral geobarometry show that a shallow, silicic chamber existed at ~4-5 km depth below the stratovolcano, while a stacked plumbing system with at least two magma storage levels at ~14 and ~24 km of depth fed the recent basalts. We interpret the wide set of observations from Ma’alalta as evidences that the area is an active rift segment, showing that localised axial extension can be heavily offset towards the rift margin.

Devastation associated with tsunamis is well known on the global scale. Flank collapse at volcanic islands is among the mechanisms triggering tsunamis, but very few examples document interaction between landslides and volcanic activity. The study of three well-preserved medieval tsunami deposits recently discovered along the coast of Stromboli volcano (Aeolian Islands, southern Italy) enabled a detailed characterization of the tsunami sequences intercalated with volcaniclastic deposits and primary tephra and allowed reconstruction of the likely sequence of volcanic events. In one case, a violent explosion possibly preceded the tsunami, whereas in the youngest event, the lateral collapse of the volcano flank triggered a tsunami wave that was rapidly followed by sustained explosive magmatic activity and ensuing prolonged ash venting. The hypothesized tsunami-triggering dynamics suggests a close link between volcanic activity and flank collapse, further confirming that the persistent activity at Stromboli makes the volcano particularly susceptible to tsunami generation.

T The paper addresses the long-lasting human presence on the island of Stromboli, an active volcano at the northern edge of the Aeolian archipelago, in the Southern Tyrrhenian sea, Italy. A conceptual model has been built to explore the phenomenon, it takes into account a series of aspects comparing Stromboli to other islands: their morphology, natural resources and geography along with the archaeological and historical data and, further, human attitude to volcanic environments, to risk and to insularity has been deeply explored. We propose a complex narrative where a combination of geological, socio-economic, historical, and psychological factors influenced people’s choices and that human presence is related more to the volcanic (and island) environment (and opportunities) than to volcanic activity.

In 79 A.D. Vesuvius buried entire cities in a few days under a blanket of pumice and ashes. It was a sudden event, which occurred after centuries of inactivity, heralded only by earthquakes that repeated periodically, for many years, creating addiction rather than alarm. After the event, the vegetation covered the volcanic products, and the memory of the disaster was lost. The first excavations began in Herculaneum in 1738 and in Pompeii ten years later, in times when archeology still did not exist. Much was destroyed, given away, thrown away. Almost intact buildings emerged, with all their contents, with many inhabitants caught on the run. The arduous process of recovering the sites has had important and not always happy stages, accompanied by continuous progress in the excavation methods. Volcanology has drawn from those experiences as much as it could, setting itself the goal of reconstructing the story of an explosive eruption, the first in the world to be described, by Pliny the Younger, the one that most left its mark on buildings, vegetation, animals and humans. Without the eruption, Pompeii and Herculaneum would have disappeared. The details on how the romans lost their lives in the tragedy is an important component to be offered to Pompeii’s visitors and that is at present largely imperfect. Knowing it and reconstructing its impact on people and the territory, going beyond the archaeological site, is an experience of the past and a warning for today and for the future.

The lava platform and the three pyroclastic cones of Vulcanello constitute the northernmost volcanic structure of the island of Vulcano (Aeolian Islands). The sandy isthmus connecting the platform to the main island was definitively formed in the first half of the 1500s; before then, Vulcano and Vulcanello were two close but separate islands. For a long time, the interpretation of the sources of the II-I century BC, had considered the islet as built up about 2200 years ago. This belief, which proliferated among naturalists from the 17th century, is not confirmed in the ancient texts or even in the geographical documents of the time, which do not indicate the presence of Vulcanello as a new and stable island near Vulcano. The islet would only be mentioned at the dawn of the second millennium, and named in Arabic “Gabal’ al Burkān”, meaning Mount of Vulcano; shortly thereafter the toponym changed to the Latin “Insulam Vulcanelli” and then, towards the 15th century, finally to Vulcanello. Since the creation of a volcanic island certainly occurred in the Aeolian Islands in the classical era, but traces of it were quickly lost, the most plausible hypothesis is that it was formed in the area of the current Vulcanello, to be subsequently erased by the sea. The shallow, flat seabed, likely remaining as a result of sea abrasion, might have represented the morphological element on which the circular lava platform we know today was formed sometime between 950 and 1000 AD.

Large-scale landslides at volcanic islands are one of the most dangerous geological phenomena, able to generate tsunamis whose effects can propagate far from the source. However, related deposits are scarcely preserved on-land in the geologic records, and are often difficult to be interpreted. Here we show the discovery of three unprecedented well-preserved tsunami deposits related to repeated flank collapses of the volcanic island of Stromboli (Southern Italy) occurred during the Late Middle Ages. Based on carbon datings, on stratigraphic, volcanological and archaeological evidence, we link the oldest, highest-magnitude investigated tsunami to the following rapid abandonment of the island which was inhabited at that time, contrary than previously thought. The destructive power of this event is also possibly related to a huge marine storm that devastated the ports of Naples in 1343 (200 km north of Stromboli) described by the famous writer Petrarch. The portrayed devastation can be potentially attributed to the arrival of multiple tsunami waves generated by a major landslide in Stromboli island, confirming the hypothetical hazard of these phenomena at a regional scale.

Understanding the dynamics and effects of hydrothermal eruptions is crucial to the hazard assessment in both volcanic and geothermal areas. Eruptions from hydrothermal centres may occur associated with magmatic phases, but also as isolated events without magmatic input, with the most recent examples being those of Te Maari (Tongariro, New Zealand) in 2012 and Ontake (Japan) in 2014. The most recent caldera of the Island of Vulcano (southern Italy) hosts in its centre the La Fossa cone, active since 5.5 ka and now characterised by continuous fumarolic degassing. In historical times, La Fossa cone has experienced several hydrothermal eruptions, with the most violent event being the Breccia di Commenda eruption that occurred during the thirteenth century ad. Based on analysis of 170 stratigraphic logs, we show that the Breccia di Commenda eruption occurred in three main phases. After an opening, low-intensity ash emission phase (phase 1), the eruption energy climaxed during phase 2, when a series of violent explosions produced an asymmetric shower of ballistic blocks and the contemporaneous emplacement of highly dispersed, lithic-rich, blast-like pyroclastic density currents (PDCs). The tephra units emplaced during phase 2, ranging in volume from 0.2 to 2.7 × 105 m3, were covered in turn by thin ash fall deposits (phase 3). The dynamics of the most violent and intense stage of the eruption (phase 2) was investigated by numerical simulations. A three-dimensional numerical model was applied, describing the eruptive mixture as a Eulerian–Eulerian, two-phase, non-equilibrium gas-particle fluid (plus a one-way coupled Lagrangian ballistic block fraction). At the initial simulation time, a mass of about 109 kg, with initial overpressure above 10 MPa, and a temperature of 250 °C, was suddenly ejected from a 200-m-long, eastward inclined, NNE–SSW trending fissure. The mass release formed blast-like PDCs on both sides of the fissure and launched ballistic blocks eastwards. Field investigations and numerical simulations confirm that hydrothermal explosions at La Fossa cone include intense ballistic fallout of blocks, emission of PDCs potentially travelling beyond the La Fossa caldera and significant ash fallout. The hazard associated with both ballistic impact and PDC ingress, as associated with hydrothermal eruption, is significantly larger with respect to that associated with Vulcanian-type events of La Fossa.

The timing of the Holocene volcanic activity of Tenerife (Canary Islands) is poorly constrained and the volcanological framework for this area is still incomplete. Most of the eruptions are dated only by a single 14C dating, or the ages are simply stratigraphically determined. We apply palaeomagnetism, increasingly used in the last years to date Holocene volcanism, to improve the knowledge of Tenerife volcanic history. We report on the palaeomagnetic dating, using the SHA.DIF.14K global model, of nine Holocene eruptions that produced scoria cones and major lava flows, and we compare our results with those previously obtained by 14C method. Four of the studied eruptions were previously dated by 14C, four were stratigraphically constrained, and one was never dated so far. Concerning the first group, for Boca Cangrejo and Mna Reventada eruptions, palaeomagnetic and 14C ages agree, while for the others we obtained older or younger ages than radiocarbon data. For the second group, one or more age ranges smaller than stratigraphic intervals were found. Finally, we provided the first dating (790–723 BCE) of the Mna Grande eruption. We confirm that palaeomagnetism can be considered an excellent complement to the radiocarbon method, because it is applicable on volcanics with nearly all compositions and provides higher resolution dating, at least where reliable geomagnetic reference curves are available. The improved framework of the Holocene volcanic activity of Tenerife shows alternating periods characterized by low and high eruptive frequencies, with the last 3 kyr characterized by high eruptive frequency and dominated by basaltic eruptions.

The increasing application of cryptotephra studies is leading the identification of new tephra marker layers the sources of which in many cases may not be known or may be ambiguous. In this contribution, we discuss the controls on tephra geochemistry in the context of establishing the provenance of an unknown tephra layer. We use the RESET database ( https://c14.arch.ox.ac.uk ), which contains major and trace element data for a number of European silicic tephra erupted in the period 100 ka to ca 10 ka, to define new and modify existing tectonic setting discrimination diagrams for use with volcanic glass analyses. Bivariate plots of the elements Rb, Nb, Ta, Y and Th and K 2 O, SiO 2 , FeO and MgO can be used to identify tephra from different tectonic settings. New, detailed glass chemistry shows that tephra from the productive Neapolitan volcanic centres, Somma-Vesuvius (22–4 ka activity), Campi Flegrei (60–15 ka) and Ischia (75–20 ka), can be separated using major elements, CaO–SiO 2 , Na 2 O/K 2 O–CaO and CaO–MgO. In each of these centres, the tephrostratigraphic record is characterized by the repeated occurrence of similar glass compositions, punctuated by significant changes in magma chemistry. The glass compositions of successive eruptions from Campi Flegrei are similar but there is a significant change in the composition following the Campanian Ignimbrite, and there are comparable compositional changes at Ischia following the Monte Epomeo Green Tuff eruption and at Somma-Vesuvius following the Verdoline event. Distinguishing different tephras from a single volcanic centre is more problematic, and in some instances even impossible, without good chronological and stratigraphic control and/or high-resolution trace element glass data. At Somma-Vesuvius certain major elements can be used to separate glasses from the major chronological phases (Group 1 – Pomici di Base and Verdoline; Group 2 – Mercato and Avellino), but separating tephras within a single group on the basis of glass composition can be problematic.

Campi Flegrei is an active volcanic area situated in the Campanian Plain (Italy) and dominated by a resurgent caldera. The great majority of past eruptions have been explosive, variable in magnitude, intensity, and in their vent locations. In this hazard assessment study we present a probabilistic analysis using a variety of volcanological data sets to map the background spatial probability of vent opening conditional on the occurrence of an event in the foreseeable future. The analysis focuses on the reconstruction of the location of past eruptive vents in the last 15 ka, including the distribution of faults and surface fractures as being representative of areas of crustal weakness. One of our key objectives was to incorporate some of the main sources of epistemic uncertainty about the volcanic system through a structured expert elicitation, thereby quantifying uncertainties for certain important model parameters and allowing outcomes from different expert weighting models to be evaluated. Results indicate that past vent locations are the most informative factors governing the probabilities of vent opening, followed by the locations of faults and then fractures. Our vent opening probability maps highlight the presence of a sizeable region in the central eastern part of the caldera where the likelihood of new vent opening per kilometer squared is about 6 times higher than the baseline value for the whole caldera. While these probability values have substantial uncertainties associated with them, our findings provide a rational basis for hazard mapping of the next eruption at Campi Flegrei caldera.

Campi Flegrei (CF) is an example of an active caldera containing densely populated settlements at very high risk of pyroclastic density currents (PDCs). We present here an innovative method for assessing background spatial PDC hazard in a caldera setting with probabilistic invasion maps conditional on the occurrence of an explosive event. The method encompasses the probabilistic assessment of potential vent opening positions, derived in the companion paper, combined with inferences about the spatial density distribution of PDC invasion areas from a simplified flow model, informed by reconstruction of deposits from eruptions in the last 15 ka. The flow model describes the PDC kinematics and accounts for main effects of topography on flow propagation. Structured expert elicitation is used to incorporate certain sources of epistemic uncertainty, and a Monte Carlo approach is adopted to produce a set of probabilistic hazard maps for the whole CF area. Our findings show that, in case of eruption, almost the entire caldera is exposed to invasion with a mean probability of at least 5%, with peaks greater than 50% in some central areas. Some areas outside the caldera are also exposed to this danger, with mean probabilities of invasion of the order of 5–10%. Our analysis suggests that these probability estimates have location-specific uncertainties which can be substantial. The results prove to be robust with respect to alternative elicitation models and allow the influence on hazard mapping of different sources of uncertainty, and of theoretical and numerical assumptions, to be quantified.

Stromboli is a persistently active, open-vent basaltic volcano whose activity is controlled by the balance between magma supply, outgassing, and eruptive rates, and is characterized by low-intensity, regular Strombolian explosions. However, two types of large, transient, violent explosive eruptions suddenly occur with no clear precursory activity. These explosions, called “major” and “paroxysmal” depending on size, cover a large variability in intensity and mag- nitude, but are all marked by short duration. Paroxysms have significantly larger intensities (>106 kg/s) than major explosions (104 kg/s) and fundamental differences in the characteris- tics (composition, crystallinity, vesicularity) of the erupted tephra, suggesting that different sources feed these two eruption types. Paroxysms are generated by the explosive fragmen- tation of low-porphyricity (LP) magma mingled with high-porphyricity resident magma in the shallow reservoir, whereas major eruptions are likely associated with destabilization of the lower portion of the shallow magmatic system, continuously hybridized by the arrival of LP magma. In general, the intensity of these explosions is related to the amount of the LP magma erupted (>107 kg in paroxysms and 104–105 kg in major explosions), suggesting that the magma plays a major role in the fragmentation mechanism. Despite its primary impor- tance in the hazards of Stromboli, the total amount of magma erupted in these events in the past 10 years is less than 1% of the total mass erupted by the volcano.

This study presents a new method for producing long-term hazard maps for pyroclastic density currents (PDC) originating at Campi Flegrei caldera. Such method is based on a doubly stochastic approach and is able to combine the uncertainty assessments on the spatial location of the volcanic vent, the size of the flow and the expected time of such an event. The results are obtained by using a Monte Carlo approach and adopting a simplified invasion model based on the box model integral approximation. Temporal assessments are modelled through a Cox-type process including self-excitement effects, based on the eruptive record of the last 15 kyr. Mean and percentile maps of PDC invasion probability are produced, exploring their sensitivity to some sources of uncertainty and to the effects of the dependence between PDC scales and the caldera sector where they originated. Conditional maps representative of PDC originating inside limited zones of the caldera, or of PDC with a limited range of scales are also produced. Finally, the effect of assuming different time windows for the hazard estimates is explored, also including the potential occurrence of a sequence of multiple events. Assuming that the last eruption of Monte Nuovo (A.D. 1538) marked the beginning of a new epoch of activity similar to the previous ones, results of the statistical analysis indicate a mean probability of PDC invasion above 5% in the next 50 years on almost the entire caldera (with a probability peak of ~25% in the central part of the caldera). In contrast, probability values reduce by a factor of about 3 if the entire eruptive record is considered over the last 15 kyr, i.e. including both eruptive epochs and quiescent periods.

Volcanic ash (1000 analyses) provides a basis for proximal-distal and distal-distal tephra correlations. Tephra deposits from the different Aeolian Islands are geochemically diverse; with some individual eruptions showing diagnostic geochemical heterogeneity recognised both stratigraphically and/or spatially. Major element glass analyses reveal that Vulcano (0-21ka) and Stromboli (4-13ka) have erupted potassic (shoshonitic and K-series) tephra with broadly overlapping compositions, but data presented here demonstrates that their eruptive products can be distinguished using either TiO2 contents or their HFSE/Th ratios. Whilst individual volcanic sources often produce successive tephra deposits with near identical major and minor element compositions through time (i.e., Lipari, Vulcano), trace element glass data can help to decipher successive eruptions. Changes in LREE and Th concentrations of volcanic glasses erupted spanning approximately the last 50ka greatly enhance the potential to discriminate successive eruptive units on Lipari. The new proximal glass database has been used to verify new (Ionian Sea; core M25/4-12) and existing distal occurrences of Aeolian Island derived tephra enabling the reassessments of past ash dispersals. Finally, proximal and distal data have been used to establish an integrated proximal-distal eruptive event stratigraphy for the Aeolian Islands.

This article presents the UNESCO Creative Cities Network (UCCN) and illustrates the theoretical and practical reasons underpinning its creation, based on the assumption that culture should be a strong component of effective development strategies. It then describes the effective functioning of the Network, and highlights two main tendencies resulting from diverse interpretations of what membership and participation should imply: on one side, the propensity to use the UUCCN membership as a branding tool used in the framework of local communication strategies to attract investors and tourists; on the other side, the tendency to effectively work jointly with the cities of the network to build a stronger identity based of effective results through cooperation activities. The article underlines how the tendency to use the membership as classic branding tool has been so far very strong within the Network, and points out some implications and consequences of this trend. But it also underlines the existence of a strong trend towards more effective collaboration and joint implementation of activities. The article finally shows that an interaction between these two tendencies emerges. The possibility to reinforce the cities’ image and brand through effective joint action and not self-referential communication is then highlighted, as a synthesis that use cooperation to build internationally acknowledged excellence.

The ice-capped Cotopaxi volcano is known worldwide for the large-scale, catastrophic lahars that have occurred in connection with historical explosive eruptions. The most recent large-scale lahar event occurred in 1877 when scoria flows partially melted ice and snow of the summit glacier, generating debris flows that severely impacted all the river valleys originating from the volcano. The 1877 lahars have been considered in the recent years as a maximum expected event to define the hazard associated to lahar generation at Cotopaxi. Conversely, recent field-based studies have shown that such debris flows have occurred several times during the last 800 years of activity at Cotopaxi, and that the scale of lahars has been variable, including events much larger than that of 1877. Despite a rapid retreat of the summit ice cap over the past century, in fact, there are no data clearly suggesting that future events will be smaller than those observed in the deposits of the last 800 years of activity. In addition, geological field data prove that the lahar triggering mechanism also has to be considered as a key input parameter and, under appropriate eruptive mechanisms, a hazard scenario of a lahar with a volume 3-times larger than the 1877 event is likely. In order to analyze the impact scenarios in the southern drainage system of the volcano, simulations of inundation areas were performed with a semi-empirical model (LAHARZ), using input parameters including variable water volume. Results indicate that a lahar 3-times larger than the 1877 event would invade much wider areas than those flooded by the 1877 lahars along the southern valley system, eventually impacting highly-urbanized areas such as the city of Latacunga.

The Island of Vulcano (Aeolian Islands, Southern Italy) consists of several volcanic edifices whose formation overlapped in time and space beginning 120 ka ago. The most recent volcano is the La Fossa cone, a 391 m-high active composite cone that began to erupt 5.5 ka ago. Eruptive activity at the La Fossa cone occurred in several cyclic phases separated by prolonged periods of erosion. The last 1000 years of eruptive activity and morphological variations in the cone and its surrounding area were investigated through a stratigraphic reconstruction. This was based on 139 natural cuts, 26 machine-excavated and 5 hand-dug trenches in the volcaniclastic succession. The revised stratigraphy of the volcanic and volcaniclastic sequence was compared with geological maps based on the Unconformity-bounded Stratigraphic Units criteria compiled in 2006–2010. It was found that the last 1000-year period can be divided into (in hierarchical order) Eruptive Clusters and Units. Several unconformities of different hierarchical order were also identified (erosional surfaces and/or palaeosols). Stratigraphic relationships with the Vulcanello products and with rhyolitic tephras related to the eruptions of Mt. Pilato (the last-formed volcanic edifice of the Island of Lipari) were fundamental in assigning a calendar age to most of the tephra units in the studied sequence. The morphological evolution of the upper part of the cone was also reconstructed in order to assess the average cone growth rate. This work suggests a new stratigraphic and chronological interpretation of the evolution and “cyclic” activity of the La Fossa cone in the last 1000 years. Several eruptions occurred in two main clusters. The stratigraphic record and morphological features reveal that the areas around the cone were affected by the deposition of reworked materials, with large amounts of tephra deposited on the steep slopes and within the major streams.

Textural and mineralogical study of high-temperature, angular blocks erupted during the Stromboli explosion of 15 March 2007 was used to make inferences on the nature and thermal state of rocks forming the subsurface of the volcano' summit crater terrace. The studied ejecta consist of lapilli tuff that formed as a result of the transformation and high temperature induration (sintering) of the basaltic scoriae, lapilli and ash originally accumulated as loose tephra during the current activity of the volcano. The main processes leading to the tephra transformation were investigated through microstructural observations, mineral and glass analyses (SEM-EDS and EMP analyses). Investigations revealed that subsolidus reactions and partial melting of the tephra occurred, at temperatures higher than 600 °C and under variable fO 2 conditions from QFM to HM buffering curves. In some blocks, evidence of high-T reheating and partial melting at the expense of secondary hydrothermal minerals was also observed. In order to track the subsolidus reheating history of the basaltic pyroclasts, a detailed study of the pseudomorphic phases and reactions after olivine, driven by iron oxidation under high-T conditions, was performed. The observed mineralogical transformation suggests that the lapilli tuff material, originating from the burial of tephra routinely accumulated by persistent Strombolian explosions within the crater terrace, were in some cases altered by the circulation of acidic fluids and were in any case reheated due to isotherm rise forced by high heat flux and gas streaming delivered by the underlying magma system. It is worth noting that the ejection of these unusual volcanic lithotypes was possible because a few days before the 15 March 2007 event, the craters were clogged with lapilli tuff material that slid into the crater bottom between 7 and 9 March. Findings of this study suggest that the scattered permanently active vents and shallow conduits of Stromboli are surrounded sideways and underneath the crater terrace, by a fairly large volume of high temperature rocks with variable degree of compaction, sintering up to partially melted. Such a spectrum of rock types is in good agreement with the conceptual model of prominent thermal zoning all around (sideway and upwards) the active magmatic system. We speculate that continuous migration upwards of isotherms led to transformation and partial melting of the normal Strombolian tephra.

Stromboli, the northernmost island of the Aeolian archipelago, is known for its persistent volcanic activity over the last several centuries and for its cone which, on clear days, is surmounted by a gas plume rising from its summit. The island hosts two settled areas: the village of Stromboli ( c. 500 inhabitants) to the NE and that of Ginostra ( c. 40 inhabitants) to the SW, both situated along the coast. In summer the number of residents grows considerably, reaching c. 5000 people. This paper provides a description of the present activity and reassesses volcanic hazards on the basis of data from a new monitoring system and from studies on the 2002–2003 and 2007 crises. The normal activity, that of mild Strombolian explosions, is occasionally interrupted by violent eruptions of variable scale (paroxysmal events) and lava flows. Volcanic hazards directly generated by eruptive activity consist of ballistic and tephra fallout, pyroclastic flows, lava flows, wildfires and minor lahars, presenting serious problems to the settled areas only occasionally. In addition to hazards directly related to eruptive phenomena, the Sciara del Fuoco depression has been the site of landslides at various scales, sometimes accompanied by the formation of tsunamis.

At Stromboli volcano (Southern Italy), only few minor precursors (gas output) have been identified for ‘major’ Strombolian explosions. We use ground-based interferometric synthetic aperture radar (GBInSAR) technology to monitor the displacement rate of the summit area of Stromboli. We analysed the 2009–2011 period. The analysis of the displacement rate has been performed by dividing the summit zone monitored by the GBInSAR into three regions, corresponding to the edge of the crater area (1 and 2), and to the slope of the NE crater (3). Pulses of rapid expansion of sector 3, of variable duration and amplitude, appear in coincidence with periods of intense activity that include lava flows and major explosions. We associate this expansion with the pressurization of the magma column that is recharged by deep-derived gas, promoting the onset of ‘major explosion-dominated’ activity.

We present a probabilistic approach to quantify the hazard posed by volcanic ballistic projectiles (VBP) and their potential impact on the built environment. A model named Great Balls of Fire (GBF) is introduced to describe ballistic trajectories of VBPs accounting for a variable drag coefficient and topography. It relies on input parameters easily identifiable in the field and is designed to model large numbers of VBPs stochastically. Associated functions come with the GBF code to post-process model outputs into a comprehensive probabilistic hazard assessment for VBP impacts. Outcomes include probability maps to exceed given thresholds of kinetic energies at impact, hazard curves and probabilistic isoenergy maps. Probabilities are calculated either on equally-sized pixels or zones of interest. The approach is calibrated, validated and applied to La Fossa volcano, Vulcano Island (Italy). We constructed a generic eruption scenario based on stratigraphic studies and numerical inversions of the 1888-1890 long-lasting Vulcanian cycle of La Fossa. Results suggest a similar to 10(-2)% probability of occurrence of VBP impacts with kinetic energies = 2.5 x 10(-3)% probability of roof perforation. (C) 2016 Elsevier B.V. All rights reserved.

Volcanic eruptions are typically characterized by the rise and discharge of magma at the surface through a single conduit/vent system. However, in some cases, the rise of magma can be triggered by the activation of eruptive fissures and/or vents located several kilometers apart. Simultaneous eruptions from multiple vents at calderas, not related to caldera collapse (e.g., ring faults) are traditionally regarded as an unusual phenomenon, the only historically reported examples occurring at Rabaul caldera, Papua New Guinea. Multiple venting within a caldera system is inherently difficult to demonstrate, owing partly to the infrequency of such eruptions and to the difficulty of documenting them in time and space. We present the first geological evidence that at 4.3 kyr ago the Solfatara and Averno vents, 5.4 km apart, erupted simultaneously in what is now the densely populated Campi Flegrei caldera (Southern Italy). Using tephrostratigraphy and geochemical fingerprinting of tephras, we demonstrate that the eruptions began almost at the same time and alternated with phases of variable intensity and magnitude. The results of this study demonstrate that multi-vent activity at calderas could be more frequent than previously thought and volcanic hazards could be greater than previously evaluated. More generally we infer that the simultaneous rise of magma and gas along different pathways (multiple decrepitation of chamber/s) could result in a sudden pressure rise within sub-caldera magmatic system.

Major, minor and trace element analysis of volcanic glass in proximal and distal ( It is evident that correlation of proximal continental and distal marine tephras, at a high level of confidence, requires a full complement of major, minor and trace element data. In conjunction with considerations of the mineralogy and morphology of juvenile deposits these data help define petrological lineages such that precise provenance can be established. Whilst a precise proximal–distal match must be based on identical major, minor and trace element concentrations it is clear that resurgent activity from a single volcano can produce magmas with identical compositions. In such cases stratigraphic relationships must complement any geochemical study. Occasionally proximal stratigraphies may be unrepresentative of the complete eruptive history because of a lack of exposure due to burial by more recent effusive and explosive activity, or sector collapse which can remove vital stratigraphy particularly on volcanic islands.

The 3.7 ka year-old Averno 2 eruption is one of the rare eruptions to have occurred in the northwest sector of the Phlegraean Fields caldera (PFc) over the past 5 ka. We focus here on the fallout deposits of the pyroclastic succession emplaced during this eruption. We present major and trace element data on the bulk pumices, along with major and volatile element data on clinopyroxene-hosted melt inclusions, in order to assess the conditions of storage, ascent, and eruption of the feeding trachytic magma. Crystal fractionation accounts for the evolution from trachyte to alkali-trachyte magmas; these were intimately mingled (at the micrometer scale) during the climactic phase of the eruption. The Averno 2 alkali trachyte represents one of the most evolved magmas erupted within the Phlegraean Fields area and belongs to the series of differentiated trachytic magmas erupted at different locations 5 ka ago. Melt inclusions record significant variations in H2O (from 0.4 to 5 wt%), S (from 0.01 to 0.06 wt%), Cl (from 0.75 up to 1 wt%), and F (from 0.20 to >0.50 wt%) during both magma crystallization and degassing. Unlike the eruptions occurring in the central part of the PFc, deep-derived input(s) of gas and/or magma are not required to explain the composition of melt inclusions and the mineralogy of Averno 2 pumices. Compositional data on bulk pumices, glassy matrices, and melt inclusions suggest that the Averno 2 eruption mainly resulted from successive extrusions of independent magma batches probably emplaced at depths of 2–4 km along regional fractures bordering the Neapolitan Yellow Tuff caldera.

The volcanic history of each active volcano is assembled through detailed field work that establishes stratigraphic position of the eruption deposits, radiometric ages and study of historical sources. The volcanic history is important for hazard assessment, thus the scientific community must validate the strength of conclusions. Fedele et al. (2011) propose a new reference chronostratigraphic framework for Holocene Phlegrean activity, and discuss the implications for the Campi Flegrei (CF) volcanic history and related volcanic hazards. In particular, the authors propose to amend the previously established Holocene chronostratigraphy of volcanic activity of Campi Flegrei caldera, presented in Di Vito et al. (1999), Orsi et al. (2004), Isaia et al. (2009). The proposed changes of Fedele et al. (2011) are based on new geochronologic data, a calibration of already existing C ages, and a stratigraphic survey (Perrotta et al. 2010). However, the new chronological data are limited and pre-existing stratigraphic studies have not been considered, and this yields an eruption chronology that is inconsistent with the actual stratigraphic framework.

Cotopaxi volcano, situated in the Eastern Cordillera of the Ecuadorian Andes, is one of the most active volcanoes on Earth. The volcano is well known for the magnificence of its almost perfectly symmetrical cone topped by ice and snow and for the destructive power of its large-scale, syneruptive lahars. This paper presents a stratigraphic study of the post–twelfth-century eruptive products that reveals the existence of 21 continuous tephra beds. Most of them were characterized from both a physical (dispersal areas, deposit volumes, peak Mass Discharge Rate [MDR] of the eruptions) and compositional point of view. New 14 C dates, linked with a new examination of historical chronicles, allow us to create a new chronostratigraphic scheme for this period of activity, which is bracketed by the emplacement of a regional tephra marker (A.D. 1140 ash bed from Quilotoa volcano) and the present day. The first period (A.D. 1150–1742) included only two moderate-intensity explosive eruptions, the oldest being possibly related to a dome disruption. In contrast, the period A.D. 1742–1880 started with two high-intensity, Plinian eruptions (maximum column heights of 25 and 29 km), followed by several short-lived but sustained, convective episodes. Deposits of pyroclastic surges and scoria flows were emplaced during some of these short-lived events and may have been related to column collapse and boiling over activity, respectively. Post-1880 activity, reported in 1904, 1906, and 1912, likely consisted of minor explosions that affected only the crater area. Our study of recent activity at Cotopaxi shows that high dispersive power (peak mass discharge rates from 1.1 to 9.3 × 10 7 kg/s) is associated with the eruption of only moderate amounts of magma (1.1 × 10 10 –6.0 × 10 11 kg, or ∼0.005–0.2 km 3 , Dense Rock Equivalent [DRE]). Additionally, al-though the past 2000 yr of activity at Cotopaxi have been interpreted to reflect a fairly uniform magma supply rate, detailed analysis of the past centuries, and a reanalysis of data from the past 2000 yr show that Cotopaxi9s eruptive activity is characterized by clusters of eruptive events that are separated by periods of long quiescence punctuated by isolated eruptions, often of slightly more evolved magma. No systematic variations in composition emerge in the time sequence. Although new magmatic phases commonly start with the eruption of mafic magma, this is not always observed. Additionally, eruption clusters may show either compositional trends of increasing SiO 2 content or abrupt compositional changes within a cluster. We interpret the temporal and compositional variations in eruptive activity to reflect the complex interplay of deep versus shallow magmatic processes. An important result from the perspective of volcanic hazards is our conclusion that, over the studied period, no clear relation exists among repose time, eruption magnitude, and magma composition. This conclusion contrasts with the periodic eruptive behavior that has been postulated at many central volcanoes worldwide, thus inviting a reexamination of other intermediate-composition volcanic systems and a reassessment of the assumption of periodic activity.

The determination of eruptive parameters is crucial in volcanology, not only to document past eruptions, but also for tephra fallout hazard assessments. In most tephra fallout studies, eruptive parameters have been determined either by empirical techniques or analytical models, but the uncertainty of such parameters is usually not well described. We have applied both empirical and analytical models to characterize the climactic phase of the 2450 BP Plinian eruption of Pululagua (BF2 layer) and explore the variations in the total erupted mass, column height and total grain size distribution. Both approaches yield comparable results in the total mass of tephra erupted (4.5 ± 1.5 × 1011 kg), while they show some discrepancies for the determination of the column height (36–20 km from empirical techniques and 30–20 km from analytical techniques). The total grain size distribution of the BF2 layers varies with the different techniques used for the calculation and significantly affects the outputs of analytical models. Furthermore, the determination of the total grain size distribution depends strongly on the number and spatial distribution of the sample location. Inverting tephra fallout deposits on the total accumulation (or thickness) gives a good constraint on the total mass erupted but not on the column height. However, inverting on individual grain size classes better constrains the possible range of column heights (but cannot resolve particle release height). Results from the inversion on individual grain size classes show that large diffusion coefficients are necessary to model the BF2 layer and might be required to model proximal tephra deposits in order not to overestimate the total erupted mass. Additionally, we used a statistical method (smoothed bootstrap approach) to quantify the uncertainty in eruptive parameters such as column height and total erupted mass. Our uncertainty analysis yields a mean total erupted mass of 4.5 ± 0.3 × 1011 kg and a mean column height of 30 ± 3 km. Results from the uncertainty analysis compare well with results from other approaches. Finally, although the climactic phase of the 2450 BP Plinian eruption of Pululagua occurred in relatively calm atmospheric conditions, our results show that the dispersion of the BF2 layer was influenced by slight northeasterly wind conditions.

On 27 February 2007, at 12.49 GMT, a new eruption of Stromboli took place with the effusion of a lava flow from a fracture cutting the flank of the NE cone, which rapidly reached the sea. The eruption had been heralded by an increase in the amplitude of tremor and flank movement since at least the 14th of February. Short-term precursors were an increase in the rate of occurrence of small landslides within the “Sciara del Fuoco” scar on the North-western flank of the volcano. A new effusive vent opened at 18.30 GMT on the Sciara del Fuoco at an height of 400 m asl. The new lava emission caused the sudden termination of the summit flow and initiated a period of non-stationary lava outpouring which ended on 2 April, 2007. The eruption has been characterized by a rapid decrease in the eruption rate after the first days and subsequently by episodic pulse increases. On the 15th of March, the increase in lava outpouring, monitored by a thermal camera, heralded by 9 min the occurrence of a violent paroxysmal explosion with the formation of an impulsive eruption column and the emission of small pumices mingled with black scoriae. The pumice had a bulk composition similar to that of the lava and of the black scoriae, but with a distinct lower content of phenocrysts. A similar feature has been repeatedly observed during the major explosive paroxysms of Stromboli. Short term precursors of the paroxysm were recorded by strainmeter and tiltmeter stations. The volcano monitoring activity has been made by a joint team of researchers from the INGV sections of Catania, Napoli, Palermo and Rome, along with researchers from the Universities of Florence, Pisa, Roma Tre, and Palermo. The scientific activity was coordinated by a Synthesis Group made up by scientists responsible for the different monitoring techniques of INGV and Universities and by the volcanic experts of Commissione Nazionale Grandi Rischi of the Prime Minister Office (Civil Protection Department). The group made a daily evaluation of the state of the volcano and transmitted its recommendations to the Civil Protection Department (DPC). Several prevention measures were adopted by DPC, the main of which were the evacuation of the coast zone when strong acceleration of the Sciara del Fuoco slope motion (occurred twice) could led to a dangerous tsunami by flank collapse (as last occurred on 30 December 2002) and four days before the 15 March paroxysm when access was prohibited to the part of the volcano above 290 m asl.

Stromboli, one of the very few tourist volcanic islands in the world in permanent state of activity, has been the site of two important volcanic crises coupled with slope failure episodes in 2002–2003 and 2007. Due to the lucky circumstance that both crises have occurred in winter, the actual consequences on people were moderate. Nevertheless, the first crisis caused a few injuries, threatened the local population and caused relevant economic losses. The emotional impact on public opinion of the 30th December 2002 tsunami acted, in particular, as a trigger for civil protection initiatives aimed at structurally improving the standard volcano safety and preparedness measures to effectively deal with future crises. The main initiatives carried out during the 2003 crisis consisted in the setting up of: 1) new geophysical and geochemical volcano surveillance networks and 2) a local, permanent scientific/civil protection structure (COA, Centro Operativo Avanzato), where signals from volcano monitoring are visualized in real time and eventually used by the personnel of the Department of Civil Protection (DPC) for immediate activation of response procedures. This was followed by the setting up, in 2005, at the (DPC) in Rome, of a centre named “Centro Funzionale Centrale Rischio Vulcanico” (CFCRV), where the most relevant monitoring signals of Italian active volcanoes are visualized in real time and where activities of simple elaboration, for hazard assessment purpose are daily carried out and data sharing within the scientific community is coordinated by civil protection personnel with training in volcanic problems. The response effectiveness of the new system was tested on February–March 2007 when a new volcanic crisis occurred. An internal DPC “state of attention” was declared by the CF 15 days before the eruption onset when seismic and deformation parameters showed an abrupt increase up to values much higher than background. On February 27th the sudden onset of explosive activity outside the main craters and the occurrence of a small landslide down slope of the active craters were detected in real time on the screens of the CFCRV and by monitoring centres of the National Institute of Geophysics and Volcanology (INGV) and University of Florence (UNIFI). This enabled the DPC to immediately activate emergency crisis procedures and start a coordinated management of the crisis between civil protection personnel in Rome and COA. As accelerating slope movements were detected by ground deformation monitoring of UNIFI, a tsunami warning was launched shortly afterward. Warnings were also declared on 8th March and 15th March when slope movements resumed and a large explosion at the central craters occurred, respectively. From the end of February to May 2007 a scientific committee named “Scientific Synthesis Group” (SSG), appointed by the DPC, made daily evaluations of impending hazards in cooperation with CFCRV. During the crisis the DPC coordinated information activities with the media and island residents. The successful managing of the crisis consisted in minimizing risk for people and meanwhile facilitating normal activities and regular access to island.

Probabilistic characterizations of possible future eruptive scenarios at Vesuvius volcano are elaborated and organized within a risk-based framework. In the EXPLORIS project, a wide variety of topics relating to this basic problem have been pursued: updates of historical data, reinterpretation of previous geological field data and the collection of new fieldwork results, the development of novel numerical modelling codes and of risk assessment techniques have all been completed. To achieve coherence, many diverse strands of evidence had to be unified within a formalised structure, and linked together by expert knowledge. For this purpose, a Vesuvius ‘Event Tree’ (ET) was created to summarise in a numerical-graphical form, at different levels of detail, all the relative likelihoods relating to the genesis and style of eruption, development and nature of volcanic hazards, and the probabilities of occurrence of different volcanic risks in the next eruption crisis. The Event Tree formulation provides a logical pathway connecting generic probabilistic hazard assessment to quantitative risk evaluation. In order to achieve a complete parameterization for this all-inclusive approach, exhaustive hazard and risk models were needed, quantified with comprehensive uncertainty distributions for all factors involved, rather than simple ‘best-estimate’ or nominal values. Thus, a structured expert elicitation procedure was implemented to complement more traditional data analysis and interpretative approaches. The structure of the Vesuvius Event Tree is presented, and some of the data analysis findings and elicitation outcomes that have provided initial indicative probability distributions to be associated with each of its branches are summarized. The Event Tree extends from initiating volcanic eruption events and hazards right through to human impact and infrastructure consequences, with the complete tree and its parameterisation forming a quantitative synoptic framework for comprehensive hazard evaluation and mapping of risk impacts. The organization of the Event Tree allows easy updating, as and when new information becomes available.

For more than sixty years languages and multilingualism have constituted essential aspects of UNESCO’s programme and this remains true today. This is due, on the one hand, to the fact that we are witnessing an unprecedented valorisation of intangible cultural heritage in all its forms, and on the other, to the fear that globalization will cause an acceleration in the disappearance of a large number of languages. In this context, UNESCO has opted in favour of languages and multilingualism, by creating a normative tool and specialized and multidisciplinary programmes.

Les langues et le multilinguisme sont depuis plus de soixante ans au cœur de la vie de l’UNESCO. Ils le sont encore aujourd’hui et plus que jamais, d’une part parce que l’on assiste a une valorisation sans precedent du patrimoine culturel immateriel sous toutes ses formes, d’autre part, du fait de la crainte de voir la mondialisation accelerer le rythme de disparition d’un grand nombre de langues. Portee par un contexte general exigeant, l’UNESCO s’est engagee en faveur des langues et du multilinguisme en elaborant un outil normatif et en mettant sur pied des programmes operationnels tant specialises que multidisciplinaires.

Impact of large-scale explosive eruptions largely depends on the dynamics of transport, dispersal and deposition of ash by the convective system. In fully convective eruptive columns, ejected gases and particles emitted at the vent are vertically injected into the atmosphere by a narrow, buoyant column and then dispersed by atmosphere dynamics on a regional scale. In fully collapsing explosive eruptions, ash partly generated by secondary fragmentation is carried and dispersed by broad co-ignimbrite columns ascending above pyroclastic currents. In this paper, we investigate the transport and dispersion dynamics of ash and lapillis during a transitional plinian eruption in which both plinian and co-ignimbrite columns coexisted and interacted. The 800 BP eruptive cycle of Quilotoa volcano (Ecuador) produced a well-exposed tephra sequence. Our study shows that the sequence was accumulated by a variety of eruptive dynamics, ranging from early small phreatic explosions, to sustained magmatic plinian eruptions, to late phreatomagmatic explosive pulses. The eruptive style of the main 800 BP plinian eruption (U1) progressively evolved from an early fully convective column (plinian fall bed), to a late fully collapsing fountain (dense density currents) passing through an intermediate transitional eruptive phase (fall + syn-plinian dilute density currents). In the transitional U1 regime, height of the convective plinian column and volume and runout of the contemporaneous pyroclastic density currents generated by partial collapses were inversely correlated. The convective system originated from merging of co-plinian and co-surge contributions. This hybrid column dispersed a bimodal lapilli and ash-fall bed whose grain size markedly differs from that of classic fall deposits accumulated by fully convective plinian columns. Sedimentological analysis suggests that ash dispersion during transitional eruptions is affected by early aggregation of dry particle clusters.