293 research outputs found
Assessing vent opening location probability at Somma-Vesuvio volcanic complex with uncertainty quantification by using Structured Expert Judgment
No full textQuantifying uncertainty is crucial for producing hazard assessments which civil protection authorities use to mitigate the associated risks. In this study we combine detailed reconstructions of volcanological datasets and inputs from Structured Expert Judgment (SEJ) to produce a first background (i.e. long-term or base-rate) probability map for vent opening location in the next Plinian or Sub-Plinian eruption of Somma-Vesuvius (SV). The SV volcano has, over its history, exhibited a large variability in eruptive styles, and a moderate but significant spatial variability in vent locations. In particular, the vent positions associated with large explosive eruptions, i.e. Plinian and Sub-Plinian, have shown shifts within the present SV caldera. Notwithstanding this moderate shift, the location of a new vent could have a major effect on the run-out and dispersal of pyroclastic density currents mainly due to the presence of the Mt. Somma barrier, as also evidenced by past deposit patterns and illustrated by 3D numerical simulations, and therefore will have important implications for hazard mitigation. Thus far, we have focused on three main objectives: i) the collection and critical review of key volcanological features (position of past vents, distribution of faults, etc.) that could influence the spatial distribution of future vent locations, organized in a specific geo-database where epistemic uncertainties related to feature spatial distributions have been quantified; ii) developing spatial probability density maps with Gaussian kernel function modelling to use with our different volcanological and geophysical datasets, and iii) the production of a background probability map for vent opening position, using weighted linear combination of spatial density maps for the identified volcanological and geophysical parameters, with uncertainties (related to both epistemic and aleatoric uncertainties) explicitly included by using SEJ. Outcomes obtained during two elicitation sessions involving about 15 experts are reported for three expert judgment weighting and pooling models: (a) the Classical Model (CM) of Cooke (1991); (b) the Expected Relative Frequency (ERF) model of Flandoli et al. (2011), and (c) the Equal Weights (EW) combination. The results of combining expert judgements with our spatial modeling of the identified variables illustrate that: a) vent opening probabilities are evenly? distributed around the caldera with a peak in correspondence with the area of the present crater but with about 50% mean probability that the vent will open in other areas of the caldera; b) there is a mean cumulative probability of about 30% that the next vent will open west of the present edifice in the so-called “Piano delle Ginestre” area; c) there is a mean probability of more than 20% that next Plinian eruption will enlarge the present SV caldera and a not negligible probability (of almost 10%) that the next Plinian or sub-Plinian eruption will have its initial vent opening outside the present outline of the SV caldera. Robustness of results have been tested by considering the effects of alternative pooling methods, sub-groups of experts with different backgrounds and experiences and sub-groups of volcanological datasets. Uncertainty analysis also allowed identification of the most controversial issues and to have a first estimate of the associated ranges
Tephra sedimentation during the 2010 Eyjafjallajökull eruption (Iceland) from deposit, radar and satellite observations
No full textThe April–May 2010 eruption of the Eyjafjallajökull volcano (Iceland) was
characterized by a nearly continuous injection of tephra into the atmosphere that affected
various economic sectors in Iceland and caused a global interruption of air traffic. Eruptive
activity during 4–8 May 2010 was characterized based on short‐duration physical
parameters in order to capture transient eruptive behavior of a long‐lasting eruption
(i.e., total grain‐size distribution, erupted mass, and mass eruption rate averaged over
30 min activity). The resulting 30 min total grain‐size distribution based on both
ground and Meteosat Second Generation‐Spinning Enhanced Visible and Infrared Imager
(MSG‐SEVIRI) satellite measurements is characterized by Mdphi of about 2 phi and a
fine‐ash content of about 30 wt %. The accumulation rate varied by 2 orders of magnitude
with an exponential decay away from the vent, whereas Mdphi shows a linear increase
until about 18 km from the vent, reaching a plateau of about 4.5 phi between 20 and
56 km. The associated mass eruption rate is between 0.6 and 1.2 × 10^5 kg s−1. In situ
sampling showed how fine ash mainly fell as aggregates of various typologies. About 5
to 9 wt % of the erupted mass remained in the cloud up to 1000 km from the vent,
suggesting that nearly half of the ash >7phi settled as aggregates within the first 60 km.
Particle sphericity and shape factor varied between 0.4 and 1 with no clear correlation
to the size and distance from vent. Our experiments also demonstrate how satellite
retrievals and Doppler radar grain‐size detection can provide a real‐time description of
the source term but for a limited particle‐size range
- The 2010 eruption of Eyjafjallajökull volcano, Iceland: Contributions from chemical and Sr-isotopic microanalytical data on tephra.
No full textAbstract su vulcano Islandese per presentazione a FIST 201
Analysis of the lahars associated with the 2011 Cordón Caulle eruption, Chile
No full textIn this study we analyse the lahar events in the area surrounding the Cordón Caulle volcano (Chile) occurred during the 2011 eruption. The main phase (4-6 June) was characterized by eruptive plumes from 7 to 11 km high which dispersed most of the tephra eastward toward Argentina, with a total estimated volume of about 1 km3. Tephra fall blanketed the region ESE and ENE from the volcano with thickness of the tephra layers between about 1 m (15 km from vent) and 0.06 m (240 km from the vent). On 10 June 2011, two lahars occurred close to the Argentina-Chile border; one lahar reached the National road 231 (at 26 km from the vent), while the second lahar reached the Provincial road 234 (65 km from the vent). At the same time, floods occurred in the town of Villa La Angostura (xx km) due to the high concentration of pyroclastic material in the river. An analysis of the lahars was carried out for the first 15 days of the eruption for the area between Cordón Caulle volcano and the town of Villa La Angostura. The spatial distribution of the potential lahar sources is modelled with an infinite slope stability model based on observed deposit grain-size and thickness, rainfall data and slope angle. Results are compared with the occurrence of lahar events during the 2011 Cordón Caulle eruption. These outcomes provide fundamental insights into lahar triggering during long-lasting volcanic eruptions and are crucial to the compilation of lahar hazard maps and emergency management plans in the South Andes volcanic region
Understanding complex evolution of intermediate to silicic linear-source Plinian eruptions: Sakurajima volcano (Japan) and Tarawera Volcanic Complex (New Zealand) as case studies
No full textPlinian eruptions are commonly fed by intermediate to silicic magmas and originate both from single central vent and from km-long eruptive fissures defined by alignments of several vents. In the latter case, multiple vents can be active at the same time or sequentially, producing a complex stratigraphy of proximal deposits in which relations between the vent(s) source and tephra beds in medial area are difficult to establish. In addition, changes in the eruptive style may occur, overlapping or following the main sustained Plinian phase, making the reconstruction of eruptions behavior over time hard to constrain. Detailed field studies of tephra deposits, together with sedimentological and textural characterization of the erupted materials can provide wide datasets to understand complex eruptive sequences often associated with linear-source Plinian eruptions. In this context we investigate the stratigraphy of the AD 1914 Taisho eruption, the most recent Plinian eruptive episode of Sakurajima Volcano (Japan). The reconstruction of the Taisho eruption, based on the chronicles and the re-interpretation of the tephra deposits, depicts an eruptive scenario in which the eruption began with a Plinian explosive phase characterized by the rise of two convective columns simultaneously from two parallel, newly-opened, fissures located on two opposite sides of the volcano. After 36-48 hours, the eruption evolved toward an effusive activity with the outpouring of andesitic lava flows for several months, accompanied by ash emissions and minor discrete Vulcanian explosions. This field-based methodology can be extend to more silicic and larger volume eruptions, as for example the ~ AD 1315 Kaharoa eruption, the youngest rhyolitic Plinian eruption of the Tarawera Volcanic Complex (New Zealand). The eruption developed from multiple vents along an 8 km linear zone and exhibited a complex succession of different eruptive styles, intensities, and dynamics over an estimated ~ 5-year period of time, including initial phreatomagmatic and Plinian explosions with associated pyroclastic density currents, extrusions of lava domes and block and ash flows. The field-based approach is an essential and rapid tool to understand the complex evolution of volcanic eruptions in various time-scales, to establish eruptive scenarios and to define potential volcanic risk associated to the large spectrum of eruptive styles presented by these eruptions
The April –May 2010 Eyjafjallajokull eruption (Iceland): tephra characteristics, eruption dynamics, and role of magma-ice-water interaction
No full textAbstract su vulcano Islandese per congresso FIST 201
Chronology and impact of the 2011 Puyehue-Cordón Caulle eruption, Chile
No full textWe present a detailed chronological reconstruction of the 2011 eruption of Puyehue-Cordón Caulle volcano (Chile) based on information derived from newspapers, scientific reports and satellite images. Chronology of associated volcanic processes and their local and regional effects (i.e. precursory activity, tephra fallout, lahars, pyroclastic density currents, lava flows) are also presented. The eruption had a severe impact on the ecosystem and on various economic sectors, including aviation, tourism, agriculture, and fishing industry. Urban areas and critical infrastructures, such as airports, hospitals and roads, were also impacted. The concentration of PM10 (Particulate Matter ≤10 microns) was measured during and after the eruption, showing that maximum safety threshold levels of daily and annual exposures were surpassed in several occasions. Probabilistic analyses showed that this combination of atmospheric and eruptive conditions has a probability of occurrence of about 1%. The management of the crisis, including evacuation of people, is discussed, as well as the comparison with the impact associated with other recent eruptions located in similar areas and having similar characteristics (i.e., Quizapu, Hudson, and Chaitén volcanoes). This comparison shows that the regions downwind and very close to the erupting volcanoes suffered very similar problems, without a clear relation with the intensity of the eruption (e.g. health problems, damage to vegetation, death of animals, roof collapse, air traffic disruptions, road closure, lahars and flooding). This suggests that a detailed collection of impact data can be largely beneficial for the development of plans for the management of an eruptive crisis and the mitigation of associated risk of the Andean region
Scavenging of sulphur, halogens and trace metals by volcanic ash: the 2010 Eyjafjallajökull eruption.
No full textThe Eyjafjallajo ̈ kull volcanic eruption in 2010 released considerable amounts of ash into the high troposphere-low stratosphere,
leading to unprecedented disruption of air traffic over Europe. The role of such fine-grained tephra in adsorbing, and
therefore rapidly scavenging, volcanogenic volatile elements such as sulphur and halogens, is explored here. We report on
results (major to trace element chemistry) of leaching experiments carried out on 20 volcanic ash samples, taken from the
deposits of the main phases of the eruption (March–April 2010), or directly while falling (5–9 May 2010). Ash leachate solutions
from Eyjafjallajo ̈ kull are dominated – among cations – by Ca and Na, and display nearly equal S:Cl:F abundances
(mean S/Cl and S/F molar ratios of 0.95 and 0.34, respectively). Abundances of major elements on surface minerals from
freshly fallen ash are found to increase linearly upon increasing distance from the eruptive vents (a proxy for in-plume residence
times). This allows for the formation rates of sulphur- and halogen-bearing surface salts to be quantified (3 x 10^-9
to 2 x 10^-8 mol m2 s-1), and for the averaged rate of in-plume ash-dissolution to be estimated (1.5 x 10^-8 mol m-2 s-1; this
sourcing the majority of cation species to soluble surface salts). These fast in-plume heterogeneous reactions are the cause of
large volatile depositions: we estimate that 282 tons of elemental S, 605 tons of Cl, and 691 tons of F were daily ground deposited
via ash over Iceland in early May 2010. Since fluorine is about 3 times more rapidly processed in the plume than S and halogens
(e.g., F is extremely reactive both in gas and aerosol forms and it is rapidly adsorbed onto ash), ash leachate
compositions are in no way representative of S:Cl:F proportions in volcanic gases, and consequently of limited use in eruption
monitoring
Potential impacts of tephra fallout from a Plinian eruption at Sakurajima volcano, Japan
No full textWe present an exposure analysis to tephra fallout for a future Plinian eruption scenario at Sakurajima volcano developed based on a new field characterization of the last Plinian eruption and a review of reports of the eruptions that occurred in the past 6 centuries. A scenario-based probabilistic hazard assessment is performed using the Tephra2 model, considering various eruption durations to reflect complex eruptive sequences of all considered reference eruptions. A quantitative exposure analysis of infrastructures and lifelines is presented primarily using open-access data. Observations drawn from a detailed impact assessment after the 2011 VEI 2 eruption of Shinmoedake (Magill et al. 2013), providing a unique illustration of the impacts from tephra fall in a similar socio-economic context, are used in parallel of the hazard and exposure analyses to identify and discuss potential vulnerable and resilient infrastructures for a future eruption of Sakurajima.
Results indicate a main eastward dispersal, with higher eruption duration increasing the hazard in proximal and reducing it in distal areas. The exposure analysis reveals that 2300 km of road network, 18 km2 urban areas and 306 km2 of agricultural lands have a 50% probability to be affected by an accumulation of tephra of 1 kg/m2 and identifies the municipalities of Kagoshima, Kanoya and Tarumizu as the most likely impacted. Finally, the 2011 eruption of Shinmoedake demonstrated that a range of mitigation measures are implemented, increasing the resilience and improving the recovery of the affected infrastructures. Nevertheless, the extent to which these mitigations actions will perform during the VEI 4 eruption presented here is unclear, and our hazard assessment indicates very high hazard levels on the Sakurajima peninsula and the neighboring municipality of Tarumizu
Sedimentation of long-lasting wind-affected volcanic plumes: the example of the 2011 rhyolitic Cordón Caulle eruption, Chile
No full textSedimentation processes and fragmentation mech- anisms during explosive volcanic eruptions can be constrained based on detailed analysis of grain-size variations of tephra deposits with distance from vent and total grain-size distribu- tion (TGSD). Grain-size studies strongly rely on deposit ex- posure and, in case of long-lasting eruptions, can be compli- cated by the intricate interplay between eruptive style, atmo- spheric conditions, particle accumulation, and deposit erosion. The 2011 Cordón Caulle eruption, Chile, represents an ideals laboratory for the study of long-lasting eruptions thanks to the good deposit accessibility in medial to distal area. All layers analyzed are mostly characterized by bimodal grain-size dis- tributions, with both the modes and the fraction of the coarse subpopulation decreasing rapidly with distance from vent and those of the fine subpopulation being mostly stable. Due to gradually changing wind direction, the two subpopulations characterizing the deposit of the first 2 days of the eruption are asymmetrically distributed with respect to the dispersal axis. The TGSD of the climactic phase is also bimodal, with the coarse subpopulation representing 90 wt% of the whole distribution. Polymodality of individual samples is related to size-selective sedimentation processes, while polymodality of the TGSD is mostly related to the complex internal texture (e.g., size and shape of vesicles) of the most abundant juvenile
Editorial responsibility: V. Manville
C. Bonadonna (*) Section des sciences de la Terre et de l’environnement, Universitè de Genève, Geneva, Switzerland e-mail: [email protected]
R. Cioni : M. Pistolesi Dipartimento di Scienze della Terra, Università di Firenze, Florence, Italy
M. Elissondo : V. Baumann Servicio Geológico Minero Argentino, Buenos Aires, Argentina
clasts. The most representative TGSD could be derived based on a combination of the Voronoi tessellation with a detailed analysis of the thinning trend of individual size categories. Finally, preferential breakage of coarse pumices on ground impact was inferred from the study of particle terminal velocity
- …
