Eruption Of Mount Etna Research Articles

Health Effects of Environmental Contamination due to Volcanic Ash from Mount Etna (Sicily, Italy) in Autumn 2002

MM4-PD-08 Introduction: During autumn 2002, a large eruption of Mount Etna (Sicily, Italy) occurred. Ash fell over the city of Catania (about 400,000 inhabitants) and the resident population experienced a public health emergency for several days. Unusually high levels of suspended particulate matter, PM10, (over 100–200 μg/m3) were recorded. The local population was alerted and the Department of Civil Protection issued emergency preventive measures. The aim of the study was to evaluate the acute health effects on mortality and hospital admissions in the area around the volcano. Methods: A time-series approach was adopted for the analysis of data (time unit = day). Health outcomes during the eruption period were compared with those from the same period of the previous year (1-day shift forward to take into account the day of the week effect). Relative risks (RR) and their 95% confidence intervals (CI) were computed. Poisson regression was used to evaluate the association between daily average PM10 and daily counts of hospital admissions for cardiovascular diseases. Results: The study observed a total of 106 days of observation for each year, corresponding to 59 days of eruption and 47 days of noneruption. No effects on overall and cause-specific mortality were observed during the eruption period. Mortality for respiratory diseases (RR = 0.46; 95% CI = 0.26–0.82) as well as hospital admissions for trauma (RR = 0.77; 95% CI = 0.67–0.88) was significantly decreased. Increases in hospital admissions for cardiovascular diseases were observed: ischemic heart diseases, RR = 1.31; 95% CI = 1.10–1.56; myocardial infarction, RR = 1.34; 95% CI = 1.02–1.76, and cerebrovascular diseases, RR = 1.24; 95% CI = 1.05–1.47. The excesses were stronger among the elderly. Daily admissions for cardiovascular diseases were not associated with PM10 levels. Discussion and Conclusions: The effects of the eruption were limited to a temporary increase in cardiovascular morbidity, especially among the elderly, possibly as a consequence of in acute stress. This phenomenon has been reported following other natural disasters. The decrease in mortality for respiratory diseases and the decrease in hospital admissions for trauma were probably a result of the precautionary measures taken during the emergency period. When planning public health measures during natural disasters, special attention should be given to risk communication.

New insights into magma dynamics during last two eruptions of Mount Etna as inferred by geochemical monitoring from 2002 to 2005

Two distinct eruptive events characterize the volcanic activity at Mount Etna during the 2002 to 2005 period. We identified signals of magma ascent preceding these eruptions by geochemical monitoring of both chemical composition and He‐isotope ratio of gas emissions from five locations in the peripheral area of the volcano. The geochemical signals are interpreted using the models proposed by Caracausi et al. (2003a, 2003b) and allow identification of episodes of magma ascent and estimation of the pressures of degassing magma. As observed for the 2001 eruption (Caracausi et al., 2003b), magma ascent probably triggered the onset of the 2002–2003 eruption, and minor events of magma ascent were observed between May and December 2003. In contrast to the previous two eruptions, the 2004–2005 eruption was not preceded by significant geochemical signals of volcanic unrest, suggesting that this eruption was mainly triggered by the failure of the upper portion of the volcanic edifice under the magmatic hydrostatic pressure in the conduits. High 3He/4He ratio revealed new volatile‐rich magma accumulation. The 2002–2003 eruption was preceded by a much shorter period of new magma accumulation from deep levels of the feeding system. Few minor signals of magma migration were detected at some of the sites during the months preceding the 2004–2005 eruption, suggesting that the degassed 3He‐depleted magma resident in the volcanic conduits was not replaced by new volatile‐rich magma. This is in agreement with the lack of explosive activity during the 2004–2005 eruption and with petrologic observations that the parent magma probably erupted in 2000 and 2001. New geochemical signals of magma ascent from the deep reservoir have been identified since June 2005, indicating that the volcanic activity of Mount Etna is evolving toward new pre‐eruptive conditions.

A complex study of Etna's volcanic plume from ground‐based, in situ and space‐borne observations

Two periods of transboundary transport of volcanic aerosols and debris following recent eruptions of Mount Etna, Italy, were examined using ground‐based and satellite spectrophotometric measurements together with Light Detection And Ranging (LiDAR) and aerosol filter observations in Athens and Thessaloniki, Greece. Independent columnar SO2 measurements from ground and space identified peaks at Greek sites after the volcanic eruptions. LiDAR measurements of the aerosol extinction at Thessaloniki and Athens performed in July 2001 have shown the height of the volcanic plume to be about 3.5 km asl and the optical thickness of the dust layer to be of the order of 3×10−3 at 532 nm. Strong ozone depletion observed at the volcano plume level by using ozonesonde ascents may be attributed to the in‐plume processes that generate reactive halogens, which in turn destroy ozone. The chemical and elemental composition of aerosol samples, taken at the Earth's surface, was analysed and confirmed the volcanic origin of the dust.

Melt inclusion record of the conditions of ascent, degassing, and extrusion of volatile‐rich alkali basalt during the powerful 2002 flank eruption of Mount Etna (Italy)

Two unusual, highly explosive flank eruptions succeeded on Mount Etna in July August 2001 and in October 2002 to January 2003, raising the possibility of changing magmatic conditions. Here we decipher the origin and mechanisms of the second eruption from the composition and volatile (H2O, CO2, S, Cl) content of olivine‐hosted melt inclusions in explosive products from its south flank vents. Our results demonstrate that powerful lava fountains and ash columns at the eruption onset were sustained by closed system ascent of a batch of primitive, volatile‐rich (≥4 wt %) basaltic magma that rose from ≥10 km depth below sea level (bsl) and suddenly extruded through 2001 fractures maintained opened by eastward flank spreading. This magma, the most primitive for 240 years, probably represents the alkali‐rich parental end‐member responsible for Etna lavas' evolution since the early 1970s. Few of it was directly extruded at the eruption onset, but its input likely pressurized the shallow plumbing system several weeks before the eruption. This latter was subsequently fed by the extrusion and degassing of larger amounts of the same, but slightly more evolved, magma that were ponding at 6–4 km bsl, in agreement with seismic data and with the lack of preeruptive SO2 accumulation above the initial depth of sulphur exsolution (∼3 km bsl). We find that while ponding, this magma was flushed and dehydrated by a CO2‐rich gas phase of deeper derivation, a process that may commonly affect the plumbing system of Etna and other alkali basaltic volcanoes.

Estimation of dispersion coefficient in the troposphere from satellite images of volcanic plumes: Application to Mt. Etna, Italy

The lateral dispersion of volcanic plumes in the troposphere is investigated using satellite images. Two plume images have been selected from the Mount Etna eruption that occurred in October/November 2002. To reproduce the satellite images two modelling approaches are presented. The first one uses deterministic trajectories released from a line source extending over a range of altitudes chosen from direct observations. The second uses stochastic trajectories from an area source located at a fixed height, where the source size and the effective diffusion coefficient are determined by data analysis. The meteorological model BOLAM (Bologna Limited Area Model) supplies the atmospheric dynamics. Both approaches reproduce the main features of the observed plumes, with differences in the cross section distribution of the density.

Feedback processes between magmatic events and flank movement at Mount Etna (Italy) during the 2002–2003 eruption

The 2002–2003 Mount Etna eruption and the associated deformation provide a unique possibility to study the relationships between volcanism and volcano instability. The sequence started with movement of the eastern volcano flank and was associated with earthquakes and the formation of surface ruptures. Then the eruption occurred from fissures at the north and south rift zones and was followed by additional flank movement, seismic swarms, and surface ruptures. The overall area of flank movement implicated more than 700 km2. In this paper we investigate how episodes of magmatic events (eruptions and intrusions) and flank movement interact. In three‐dimensional numerical models we simulate the volcano‐tectonic events and calculate changes in the static stress field. The models suggest that the 2002–2003 events are the result of interrelated processes consisting of (1) the preeruptive intrusion of magma and inflation of the volcano, which induced (2) the movement of the volcano east flank, (3) facilitated the eruption, and (4) led to the slip of a much larger part of the eastern and southeastern flanks. Understanding the precise interconnectivity of these processes may help to forecast the behavior during future volcanic crisis at Mount Etna, which is crucial in minimizing volcanic and seismic hazards on the highly populated eastern sector of the volcano.

Contrasting triggering mechanisms of the 2001 and 2002–2003 eruptions of Mount Etna (Italy)

Mount Etna produced two significant eruptions in 2001 and 2002–2003, which we have analysed using geological, seismic and deformation data. These eruptions showed some similarities, such as the activating of two magmatic plumbing systems (central–lateral and eccentric), but they differed in their triggering mechanisms. While the 2001 eruption was largely the result of the emplacement of a N–S eccentric dike (independent from the central conduits) consistent with E–W regional extension, the 2002–2003 eruption occurred in response to a major flank slip on the eastern and southeastern sides of the volcano. This is demonstrated by the spatial and temporal distribution of seismicity and deformation preceding and accompanying the two eruptions. During the months prior to the 2001 eruption, most epicenters were concentrated on the southern flank, at depths of 5–15 km below sea level. During the 4 days before the eruption, earthquake hypocenters migrated to shallower levels (from 5 km bsl. upward) indicating the emplacement of the eccentric dike. This is confirmed by the patterns of ground fracturing observed in the field and deformation documented by electronic distance measurements (EDM). In contrast, the months before the 2002–2003 eruption were characterised by shallower seismicity, mainly concentrated along the active faults bordering the slipping flank sector. Flank slip accelerated in September 2002 and a second, more vigorous acceleration of flank slip occurred on 26–27 October 2002, accompanying the opening of eruptive vents. The very short (2 h) seismic crisis preceding the onset of eruptive activity stands in neat contrast with the 4 days of intense seismicity before the 2001 eruption. Subsequently, flank slip-deformation extended all over the eastern and southeastern flanks of the volcano, causing serious damage in this sector. The events of 2001–2003 can be seen as a continuous chain of intimately interacting processes including regional tectonics, magma accumulation and eruption, and flank instability. In this scenario the 2001 eruption led to increased flank instability that subsequently accelerated and culminated with the massive flank slip, which in turn facilitated the 2002–2003 eruption. This sequence of events points to a long-term feedback mechanism between magmatism and flank instability at Etna.

Experimental and analytical modeling of basaltic ash explosions at Mount Etna, Italy, 2001

The summer 2001 flank eruption of Mount Etna ended with repeated basaltic ash explosions. The explosions were similar to small‐scale Vulcanian blasts and probably originated when a plug of magma at the top of the conduit became overpressurized. We use three independent methods to estimate the overpressure in the plug: (1) To determine the pressure differential required to fragment the plug, we use a shock tube apparatus to heat and pressurize ballistic blocks at temperature T up to 900°C and pressure P up to 25 MPa and rapidly decompress them to ambient conditions; (2) we apply a model to determine the overpressure generated by microlite growth at depth because pyroclasts from the explosions have 35 vol % more microlites than preceding Strombolian product; and (3) we relate the range of ballistic blocks to their exit velocity and, with models for Vulcanian eruptions, the exit velocity to pressure in the conduit. Experiments and ejecta range bracket the overpressure driving the explosions between ∼3 and ∼5 MPa: below 2.5 MPa the blocks would not reach the observed range, but above 5 MPa the existing blocks with 20% porosity would not survive the explosions. Crystallization of 35 vol % microlites at a depth of ∼100 m increases the pressure in the plug to ∼6 MPa above atmospheric, enough to drive the explosions, with a possible contribution from deeper volatiles. Combining the different methods, we also constrain the exsolved water at fragmentation at ∼0.05 wt % and provide inferences on how the explosions came to an end.

The influence of conduit processes on changes in style of basaltic Plinian eruptions: Tarawera 1886 and Etna 122 BC

Basaltic volcanism is most typically thought to produce effusion of lava, with the most explosive manifestations ranging from mild Strombolian activity to more energetic fire fountain eruptions. However, some basaltic eruptions are now recognized as extremely violent, i.e., generating widespread phreatomagmatic, subplinian and Plinian fall deposits. We focus here on the influence of conduit processes, especially partial open-system degassing, in triggering abrupt changes in style and intensity that occurred during two examples of basaltic Plinian volcanism. We use the 1886 eruption of Tarawera, New Zealand, the youngest known basaltic Plinian eruption and the only one for which there are detailed written eyewitness accounts, and the well-documented 122 BC eruption of Mount Etna, Italy, and present new grain size and vesicularity data from the proximal deposits. These data show that even during extremely powerful basaltic eruptions, conduit processes play a critical role in modifying the form of the eruptions. Even with very high discharge, and presumably ascent, rates, partial open-system behaviour of basaltic melts becomes a critical factor that leads to development of domains of largely stagnant and outgassed melt that restricts the effective radius of the conduit. The exact path taken in the waning stages of the eruptions varied, in response to factors which included conduit geometry, efficiency and extent of outgassing and availability of ground water, but a relatively abrupt cessation to sustained high-intensity discharge was an inevitable consequence of the degassing processes.

Rapid morphological changes at the summit of an active volcano: reappraisal of the poorly documented 1964 eruption of Mount Etna (Italy)

While the eruptive record of Mount Etna is reasonably complete for the past 400 years, the activity of the early and late 1960s, which took place at the summit, is poorly documented in the scientific literature. From 1955 to 1971, the Central and Northeast Craters were the sites of long-lived mild Strombolian and effusive activity, and numerous brief episodes of vigorous eruptive activity, which led to repeated overflows of lava onto the external flanks of the volcano. A reconstruction of the sequence of the more important of these events based on research in largely obscure and nearly inaccessible sources permits a better understanding of the eruption dynamics and rough estimates of erupted volumes and of the changes to the morphology of the summit area. During the first half of 1964, the activity culminated in a series of highly dynamic events at the Central Crater including the opening of a fissure on the E flank of the central summit cone, lava fountains, voluminous tephra emission, prolonged strong activity with continuous lava overflows, and growth of large pyroclastic intracrater cones. Among the most notable processes during this eruption was the breaching of a section of the crater wall, which was caused by lateral pressure of lava ponding within the crater. Comparison with the apparently similar summit activity of 1999 allows us to state that (a) lava overflows from large pit craters at the summit are often accompanied by breaching of the crater walls, which represents a significant hazard to nearby observers, and that (b) eruptive activity in 1999 was much more complex and voluminous than in 1964. For 1960s standards however, the 1964 activity was the most important summit eruption in terms of intensity and output rates for about 100 years, causing profound changes to the summit morphology and obliterating definitively the former Central Crater.

Plume chemistry provides insights into mechanisms of sulfur and halogen degassing in basaltic volcanoes

This paper deals with sulfur, chlorine and fluorine abundances in the eruptive volcanic plume of the huge October 2002–January 2003 eruption of Mount Etna, aiming at relating the relevant compositional variations observed throughout with changes in eruption dynamics and degassing mechanisms. The recurrent sampling of plume acidic volatiles by filter-pack methodology revealed that, during the study period, S/Cl and Cl/F ratios ranged from 0.1–6.8 and 0.9–5.6, respectively. Plume S/Cl ratios increased by a factor of ∼10 as volcanic activity drifted from paroxysmal lava fountaining (mid- and late November) to passive degassing and minor effusion (early January), and then decreased to the low values (S/Cl=0.1) typical of the final stages of the eruption. Parallel variations in chlorine to fluorine ratios were also observed. A theoretical model is proposed for quantitative interpretation of these changes in plume composition. The model calculates the composition of a volatile phase exsolving from an ascending Etna magma, based on knowledge of solubilities and abundances in the undegassed melt of sulfur and halogens [T.M. Gerlach, EOS 72 (1991), 249, 254–255]. According to this model, degassing of Etnean basaltic melt at high pressures and depths (>100 MPa, 3 km) is likely to release a CO2+H2O-rich vapor phase with S/Cl molar ratios ∼1. Extensive sulfur and chlorine degassing from the melt would take place at shallower depth (P<20 MPa, 0.6 km), with S/Cl ratios in the vapor phase increasing as pressure drops to 0.1 MPa. Comparisons between model compositions and volcanic plume data demonstrate that the chemical trends observed during the eruption may be explained by increased degassing due to depressurization of a basaltic magma batch ascending toward the surface.

Plume chemistry provides insights into mechanisms of sulfur and halogen degassing in basaltic volcanoes

This paper deals with sulfur, chlorine and fluorine abundances in the eruptive volcanic plume of the huge October 2002–January 2003 eruption of Mount Etna, aiming at relating the relevant compositional variations observed throughout with changes in eruption dynamics and degassing mechanisms. The recurrent sampling of plume acidic volatiles by filter-pack methodology revealed that, during the study period, S/Cl and Cl/F ratios ranged from 0.1–6.8 and 0.9–5.6, respectively. Plume S/Cl ratios increased by a factor of ∼10 as volcanic activity drifted from paroxysmal lava fountaining (mid- and late November) to passive degassing and minor effusion (early January), and then decreased to the low values (S/Cl=0.1) typical of the final stages of the eruption. Parallel variations in chlorine to fluorine ratios were also observed. A theoretical model is proposed for quantitative interpretation of these changes in plume composition. The model calculates the composition of a volatile phase exsolving from an ascending Etna magma, based on knowledge of solubilities and abundances in the undegassed melt of sulfur and halogens [T.M. Gerlach, EOS 72 (1991), 249, 254–255]. According to this model, degassing of Etnean basaltic melt at high pressures and depths (>100 MPa, 3 km) is likely to release a CO2+H2O-rich vapor phase with S/Cl molar ratios ∼1. Extensive sulfur and chlorine degassing from the melt would take place at shallower depth (P<20 MPa, 0.6 km), with S/Cl ratios in the vapor phase increasing as pressure drops to 0.1 MPa. Comparisons between model compositions and volcanic plume data demonstrate that the chemical trends observed during the eruption may be explained by increased degassing due to depressurization of a basaltic magma batch ascending toward the surface.

Differences in Landsat TM derived lava flow thermal structures during summit and flank eruption at Mount Etna

The simultaneous solution of the Planck equation (the so-called “dual-band” technique) for two shortwave infrared Landsat Thematic Mapper (TM) bands allows an estimate of the fractional area of the hottest part of an active flow and the temperature of the cooler crust. Here, the dual-band method has been applied to a time series of Mount Etna eruptions. The frequency distribution of the fractional area of the hottest component reveals specific differences between summit and flank lava flows. The shape of the density function shows a trend consistent with a Gaussian distribution and suggests a relationship between the moments of the distribution and the emplacement environment. Because flow composition of Etnean lavas generally remains constant during the duration of their emplacement, it appears that the shape of any particular frequency distribution is probably related to fluid mechanical aspects of flow emplacement that affect flow velocity and flow heat loss and thus the rate of formation of the surface crust. These factors include the influence of topographical features such as changes in slope gradient, changes in volume effusion rate, and progressive downflow increases in bulk or effective viscosity. A form of the general theoretical solution for the ‘dual-band’ system, which illustrates the relationship between radiance in TM bands 5 and 7, corresponding to hot fractional area and crust temperature, is presented. Generally speaking, it appears that for a given flow at any point in time, larger fractional areas of exposed hot material are correlated with higher temperatures and that, while the overall shape of that distribution is common for the flows studied, its amplitude and slope reflect individual flow rheological regimes.

The application of AVHRR data for the detection of volcanic ash in a Volcanic Ash Advisory Centre

AbstractA volcanic ash detection product using AVHRR data has been developed for use in the London Volcanic Ash Advisory Centre, operated by forecasters at the Met Office. The product is an image that shows the brightness temperature difference between two infrared channels, which can be used to discriminate between clouds containing volcanic ash particles and those containing water droplets or ice crystals. Factors such as water vapour, water droplet and ice crystal content, opacity, cloud top temperature, ash particle size, surface emissivity properties and instrumental effects all have an effect on the spectral signal represented in the image. AVHRR imagery has been used to study the volcanic clouds ejected from eruptions of Mount Etna (Italy) in July 2001, Hekla (Iceland) in February 2000 and Mount Spurr (USA) in September 1992 to demonstrate the application of this product during volcanic events. The volcanic ash detection product provides essential information that can help forecasters locate volcanic ash and give appropriate guidance through advisory statements to the aviation industry and thus help avoid dangerous and expensive encounters between aircraft and volcanic ash. Copyright © 2003 Royal Meteorological Society.

Bulk processes prior to the 2001 Mount Etna eruption, highlighted through microgravity studies

Discrete gravity data were acquired at Mount Etna over a period lasting more than a year and spanning the July–August 2001 flank eruption. The gravity measurements were made using a Scintrex CG‐3M gravimeter along two profiles of Etna's gravity network. The gravity data indicate that during the second half of 2000, a mass increase of 2 × 1010 kg took place about 1.5 km below the summit craters zone. It is thought to be due to a magma accumulation. A comparable mass decrease was detected during a 4‐month period encompassing the eruption which is thought to be the result of withdrawal of the same magma. The gravity data also show that a mass decrease of 2.5 × 1011 kg occurred between January and 19 July 2001 (2 days after the start of the eruption), below the southeastern sector of the volcano, within a volume around 2.5 km below sea level. This decrease was followed by a sudden increase that, in 14 days, partially compensated the previous variation. Since many tensional earthquakes took place during the first half of 2001, within the same source volume of the inferred mass decrease, it is reasonable to assume that the variation observed before the eruption reflects the formation of new voids by tectonic tensile stresses below the volcano edifice. Magma was emplaced along the new formed path from a deep storage to higher levels of Etna's plumbing system, setting off the eruption and causing the gravity increase observed soon after its start. Vulcanological, petrological, and ground deformation studies agree with the assumption of a batch of magma coming directly from a deep storage to have supplied most material extruded during the eruption.

Estimation of the 2002 Mount Etna eruption cloud radiative forcing from Meteosat-7 data

On 27th October 2002, after 15 months of small activity, the Mount Etna located on the island of Sicily, Italy (37.73°N, 15.00°E) erupted undergoing one of its most vigorous eruptions in years. During a few days, Europe's highest and most active volcano hurled lava and spewed significant amounts of ash and trace gases into the atmosphere. The smoke and ash plume originating from the volcano stretched from the Sicily to the north African coast. The plume from the volcano has been identified and tracked using half-hourly Meteosat-7 visible, infrared, and water vapor imagery in order to estimate the radiative forcing produced by the introduction of the volcanic cloud in a previously clear sky. Our results indicate that, while the volcanic cloud has introduced a well-discernable radiative perturbation, the magnitude of the shortwave volcanic forcing appears in the range of the one introduced by large clouds above the Mediterranean Sea. By contrast, the perturbation generated in the longwave spectrum at the top of the atmosphere is larger than the one introduced by large meteorological clouds.

Structural features of the July–August 2001 Mount Etna eruption: evidence for a complex magma supply system

We describe the evolution of the volcanic activity and deformation patterns observed at Mount Etna during the July–August 2001 eruption. Seismicity started at 3000 m below sea level on 13 July, accompanied by moderate ground swelling. Ground deformation culminated on 16 July with the development of a NE–SW graben c . 500 m wide and c . 1 m deep in the Cisternazza area at 2600–2500 m above sea level on the southern slope of the volcano. On 17 July, the eruption started at the summit of Mount Etna from the SE Crater (central–lateral eruptive system), from which two radial, c . 30 m wide, c . 3000 m long fracture zones, associated with eruptive fissures, propagated both southward (17 July) and northeastward (20 July). On 18 July, a new vent formed at 2100 m elevation, at the southern base of the Montagnola, followed on the next day by the opening of a vent further upslope, at 2550 m (eccentric eruptive system). The eruption lasted for 3 weeks. Approximately 80% of the total lava volume was erupted from the 2100 m and the 2550 m vents. The collected structural data suggest that the Cisternazza graben developed as a passive local response of the volcanic edifice to the ascent of a north–south eccentric dyke, which eventually reached the ground surface in the Montagnola area (18–19 July). In contrast, the two narrow fracture zones radiating from the summit are interpreted as the lateral propagation, from the conduit of the SE Crater, of north–south- and NE–SW-oriented shallow dykes, 2–3 m wide. The evolution of the fracture pattern together with other volcanological data (magma ascent and effusion rate, eruptive style, petrochemical characteristics of the erupted products, and petrology of xenoliths within magma) suggest that the eccentric and central–lateral eruptions were fed by two distinct magmatic systems. Examples of eccentric activity accompanied by central–lateral events have never been described before at Etna.

What makes flank eruptions? The 2001 Etna eruption and its possible triggering mechanisms

Most flank eruptions within a central stratovolcano are triggered by lateral draining of magma from its central conduit, and only few eruptions appear to be independent of the central conduit. In order to better highlight the dynamics of flank eruptions in a central stratovolcano, we review the eruptive history of Etna over the last 100 years. In particular, we take into consideration the Mount Etna eruption in 2001, which showed both summit activity and a flank eruption interpreted to be independent from the summit system. The eruption started with the emplacement of a ~N-S trending peripheral dike, responsible for the extrusion of 75% of the total volume of the erupted products. The rest of the magma was extruded through the summit conduit system (SE crater), feeding two radial dikes. The distribution of the seismicity and structures related to the propagation of the peripheral dike and volumetric considerations on the erupted magmas exclude a shallow connection between the summit and the peripheral magmatic systems during the eruption. Even though the summit and the peripheral magmatic systems were independent at shallow depths (<3 km b.s.l.), petro-chemical data suggest that a common magma rising from depth fed the two systems. This deep connection resulted in the extrusion of residual magma from the summit system and of new magma from the peripheral system. Gravitational stresses predominate at the surface, controlling the emplacement of the dikes radiating from the summit; conversely, regional tectonics, possibly related to N-S trending structures, remains the most likely factor to have controlled at depth the rise of magma feeding the peripheral eruption.

S, Cl and F degassing as an indicator of volcanic dynamics: The 2001 eruption of Mount Etna

The recent eruption of Mount Etna (July 2001) offered the opportunity to analyze magma‐derived volatiles emitted during pre‐ and syn‐eruptive phases, and to verify whether their composition is affected by changes in volcanic dynamics. This paper presents the results of analyses of F, Cl and S in the volcanic plume collected by filter‐packs, and interprets variations in the composition based on contrasting solubility in magmas. A Rayleigh‐type degassing mechanism was used to fit the acquired data and to estimate Henry's solubility constant ratios in Etnean basalt. This model provided insights into the dynamics of the volcano. Abundances of sulfur and halogens in eruptive plumes may help predict the temporal evolution of an ongoing effusive eruption.

Volumetric observations during paroxysmal eruptions at Mount Etna: pressurized drainage of a shallow chamber or pulsed supply?

The October 17 to November 5, 1999, eruption of Mount Etna’s Bocca Nuova crater emplaced a ∼15×10 6 m 3 flow field. The eruption was characterized by 11 paroxysmal events during which intense Strombolian and lava fountain activity fed vigorous channelized ′a′a flows at eruption rates of up to 120 m 3 s −1. Each paroxysm lasted between 75 and 450 min, and was separated by periods of less intense Strombolian activity and less vigorous (<10 m 3 s −1) effusion. Ground-based, satellite- and model-derived volumetric data show that the eruption was characterized by two periods during which eruption rates and cumulative volume showed exponential decay. This is consistent with a scenario whereby the system was depressurized during the first eruptive period (October 17–23), repressurized during an October 24 pause, and then depressurized again during the second period (October 25–28). The imbalance between the erupted and supplied volumes mean that the two periods involved the collection of 1.5–5.7×10 6 m 3 and 1.2–3.6×10 6 m 3, respectively, or an increase in the time-averaged supply to 11.6–13.6 m 3 s −1 and 12.5–14.9 m 3 s −1. Two models are consistent with the observed episodic fountaining, derived volumetric trends and calculated volume imbalance: a magma collection model and a pulsed supply model. In the former case, depressurization of a shallow reservoir cause the observed volumetric trends and foam collapse at the reservoir roof powers fountaining. In the pulsing case, variations in magma flux account for pressurization–depressurization and supply the excess volume. Increases in rise rate and volatile flux, coupled with rapid exsolution during ascent, trigger fountaining. Limiting equations that define critical foam layer volumes and magma rise rates necessary for Hawaiian-style fountaining favor the latter model.