Dynamics of volcanic eruptions
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The state of stress in the Earth's crust is a fundamental geophysical variable. That stress is transmitted across the boundaries between magma bodies and their host rocks, forming an undoubted potential causal link. But for almost all... more
The state of stress in the Earth's crust is a fundamental geophysical variable. That stress is transmitted across the boundaries between magma bodies and their host rocks, forming an undoubted potential causal link. But for almost all volcanoes we have no direct observational knowledge of the state of stress within and below them. We know, in general, that the 3D field of stress acting on a volcanic system can dramatically affect eruption dynamics controlling processes of magma storage and magma ascent to the surface. Stresses act at different scales, and both local to regional stress can significantly affect rock-magma mechanics in a very complex way because of nonlinear interactions between the different parts of the volcanic system and heterogeneity of the Earth's crust. A change in stress within the magmatic system can play a fundamental role in triggering or modifying the style of volcanic eruptions, and even reawakening a dormant system. There are many forcing agents of changes in stress, including earthquakes, erosion and landslides, deglaciation, and tidal effects. The local stress can change also as response of magma influx from deeper reservoirs and an increase of the magma/gas pressure. Such changes can occur on different time scales dictating variations in the behavior of a volcanic system. Change in local tectonic stress has been invoked as a trigger of large ignimbrite eruptions or for controlling the eruptive style of explosive eruptions. Sometimes volcano systems that are closely located may become active in chorus after strong earthquakes. Some studies suggest that volcanic eruptions are triggered if compressive stress acts at the magma system and " squeezes " out magma (Rikitake and Sato, 1989). Other studies suggest that horizontally extensional stress fields facilitate magma rise and thus encourage eruptions (e.g., Gudmundsson, 1990, 2006), or that fluctuating compression and extension during the passing of seismic waves trigger eruptions (Walter and Amelung, 2007; Watt et al., 2009). Stress-sensitive volcanic processes are generally not well understood and we urgently need new observational techniques and improved analytical tools to improve that understanding. All these considerations inspired the Research Topic on " Stress field control of eruption dynamics, " which aimed for a thorough discussion about the state of the art, new ideas, perspectives, and challenges of the interplay between stress fields and volcanic activity. The papers comprising the Research Topic cover a broad range of stress mechanisms affecting volcanic activity. Two reviews introduce the influence of stress change on eruption initiation and dynamics (Sulpizio and Massaro) and stress control on monogenetic volcanism (Martì et al.). The large-scale influence of tectonic stress on volcanism is discussed in two other papers (Wadge et al. Paguican and Bursik), which focus on the East African Rift and the Hat Creek Graben region, USA, respectively. The role of local stress in distinct volcanic scenarios is presented in three papers: syn-eruptive dynamics during caldera forming events (Costa and Martì), the opening of new vents at a mature stratovolcano like Etna (Acocella et al.), and the distribution of eruptive fissures due to
An ephemeral (and proximal) outcrop at the quaternary basaltic Puig de la Garrinada cinder volcano was studied in order to decipher eruptive mechanism variations in the course of a single eruption. Once the volcanostratigraphy was... more
An ephemeral (and proximal) outcrop at the quaternary basaltic Puig de la Garrinada cinder volcano was
studied in order to decipher eruptive mechanism variations in the course of a single eruption. Once the
volcanostratigraphy was established (and recorded by photographs), a very detailed sampling of underlying
lava flows, bombs and a large number of fine-sized lapilli and ash beds was carried out. An ad hoc description
card was elaborated for study under stereo microscope in order to identify the different types of materials
that form the volcanic cone. Ten material types were recognised: sedimentary accidental clasts, massive lava
accidental clasts, bombs, xenoliths, xenocrysts and phenocrysts, oxidised scoria, scoria with oxidised film,
fluidal pyroclasts, non-fluidal pyroclasts, and coatings. Subsequent studies under SEM+EDS and basic
chemical characterization of the samples (whole rock XRF for major and trace elements) and EMPA were
conducted. All these studies make possible the reconstruction of the eruptive history of the La Garrinada
volcano, which shows a transition from initial strombolian activity to gradually incorporated phreatomagmatic
activity. This permits the calculation of magma eruption rates, magma column oscillations and aquifer
interactions with magma column. Since our general conclusions agree well with the discrimination of
eruptive episodes obtained from the stereo microscope description card, macroscopic volcanostratigraphy
and chemical results, it is proposed that a similar study protocol (quick volcanostratigraphy logging,
photographic record, detailed sampling, description following this card) might be useful in the
reconstruction of eruptive activity of other cinder cones in the Garrotxa region and elsewhere, and therefore
can provide a good and quick methodological tool, especially when rapid field description and sampling is
required (ephemeral outcrops, risky sampling during active eruptive episodes, etc.). Moreover, the conducted
sampling allows for subsequent studies on the same set of pyroclasts.
studied in order to decipher eruptive mechanism variations in the course of a single eruption. Once the
volcanostratigraphy was established (and recorded by photographs), a very detailed sampling of underlying
lava flows, bombs and a large number of fine-sized lapilli and ash beds was carried out. An ad hoc description
card was elaborated for study under stereo microscope in order to identify the different types of materials
that form the volcanic cone. Ten material types were recognised: sedimentary accidental clasts, massive lava
accidental clasts, bombs, xenoliths, xenocrysts and phenocrysts, oxidised scoria, scoria with oxidised film,
fluidal pyroclasts, non-fluidal pyroclasts, and coatings. Subsequent studies under SEM+EDS and basic
chemical characterization of the samples (whole rock XRF for major and trace elements) and EMPA were
conducted. All these studies make possible the reconstruction of the eruptive history of the La Garrinada
volcano, which shows a transition from initial strombolian activity to gradually incorporated phreatomagmatic
activity. This permits the calculation of magma eruption rates, magma column oscillations and aquifer
interactions with magma column. Since our general conclusions agree well with the discrimination of
eruptive episodes obtained from the stereo microscope description card, macroscopic volcanostratigraphy
and chemical results, it is proposed that a similar study protocol (quick volcanostratigraphy logging,
photographic record, detailed sampling, description following this card) might be useful in the
reconstruction of eruptive activity of other cinder cones in the Garrotxa region and elsewhere, and therefore
can provide a good and quick methodological tool, especially when rapid field description and sampling is
required (ephemeral outcrops, risky sampling during active eruptive episodes, etc.). Moreover, the conducted
sampling allows for subsequent studies on the same set of pyroclasts.
The Pomici di Avellino eruption is the Plinian event of Vesuvius with the highest territorial impact. It affected an area densely inhabited by Early Bronze Age human communities and resulted in the long-term abandonment of an extensive... more
The Pomici di Avellino eruption is the Plinian event of Vesuvius with the highest territorial impact. It affected an area densely inhabited by Early Bronze Age human communities and resulted in the long-term abandonment of an extensive zone surrounding the volcano. Traces of human life beneath the eruption products are very common throughout the Campania Region. A systematic review of the available archaeological data, the study of geological and archaeological sequences exposed in excavations , and the reconstruction of the volcanic phenomena affecting single sites has yielded an understanding of local effects and their duration. The archaeological and volcanological analyses have shown that the territory was rapidly abandoned before and during the eruption, with rare post-eruption attempts at resettlement of the same sites inhabited previously. The definition of the distribution and stratigraphy of alluvial deposits in many of the studied sequences leads us to hypothesise that the scarce presence of humans during phases 1 and 2 of the Middle Bronze Age in the wide area affected by the eruption was due to diffuse phenomena of remobilisation of the eruption products, generating long-lasting alluvial processes. These were favoured by the deposition of loose fine pyroclastic material on the slopes of the volcano and the Apennines, and by climatic conditions. A significant resettlement of the territory occurred only hundreds of years after the Pomici di Avellino eruption, during phase 3 of the Middle Bronze Age. This study show the role of volcanic and related phenomena from a Plinian event in the settlement dynamics of a complex territory like Campania.
A new fluid-dynamic model is developed to numerically simulate the non-equilibrium dynamics of polydis-perse gas–particle mixtures forming volcanic plumes. Starting from the three-dimensional N-phase Eulerian transport equations for a... more
A new fluid-dynamic model is developed to numerically simulate the non-equilibrium dynamics of polydis-perse gas–particle mixtures forming volcanic plumes. Starting from the three-dimensional N-phase Eulerian transport equations for a mixture of gases and solid dispersed particles, we adopt an asymptotic expansion strategy to derive a com-pressible version of the first-order non-equilibrium model, valid for low-concentration regimes (particle volume fraction less than 10 −3) and particle Stokes number (St – i.e., the ratio between relaxation time and flow characteristic time) not exceeding about 0.2. The new model, which is called ASHEE (ASH Equilibrium Eulerian), is significantly faster than the N-phase Eulerian model while retaining the capability to describe gas–particle non-equilibrium effects. Direct Numerical Simulation accurately reproduces the dynamics of isotropic, compressible turbulence in subsonic regimes. For gas–particle mixtures, it describes the main features of density fluctuations and the preferential concentration and clustering of particles by turbulence, thus verifying the model reliability and suitability for the numerical simulation of high-Reynolds number and high-temperature regimes in the presence of a dispersed phase. On the other hand, Large-Eddy Numerical Simulations of forced plumes are able to reproduce the averaged and instantaneous flow properties. In particular , the self-similar Gaussian radial profile and the development of large-scale coherent structures are reproduced, including the rate of turbulent mixing and entrainment of atmospheric air. Application to the Large-Eddy Simulation of the injection of the eruptive mixture in a stratified atmosphere describes some of the important features of turbulent volcanic plumes, including air entrainment, buoyancy reversal and maximum plume height. For very fine particles (St → 0, when non-equilibrium effects are negligible) the model reduces to the so-called dusty-gas model. However, coarse particles partially decouple from the gas phase within eddies (thus modifying the turbulent structure) and preferentially concentrate at the eddy periphery, eventually being lost from the plume margins due to the concurrent effect of gravity. By these mechanisms, gas–particle non-equilibrium processes are able to influence the large-scale behavior of volcanic plumes.
Planchón-Peteroa volcano started a renewed eruptive period between January 2010 and July 2011. This eruptive period was characterized by the occurrence of 4 explosive eruptive phases, dominated by low-intensity phreatic activity, which... more
Planchón-Peteroa volcano started a renewed eruptive period between January 2010 and July 2011. This eruptive period was characterized by the occurrence of 4 explosive eruptive phases, dominated by low-intensity phreatic activity, which produced almost permanent gas/steam columns (200-800 m height over the active crater). Those columns presented frequently scarce ash, and were interrupted by phreatic explosions that produced ash columns 1,000-3,000 m height in the more intense periods. Eruptive plumes were transported in several directions (NW, N, NE, E and SE), but more than half of the time the plume axis was 130-150° E, and reached a distance up to 638 km from the active crater. Tephra fall deposits identified in the NW, N, NE, E and SE flanks covered an area of 1,265 km 2 , thickness variable from 4 m (SE border of active crater) to ~0.5 cm 36.8 km SE and ~8 km NW from active crater, respectively, corresponding to a minimum volume of 0.0088 km 3. Tephra fall deposit is exclusively constituted of no juvenile fragments including: lithics fragments as main component, quartz and plagioclase crystals, some oxidized lithics, and occasional presence of Fe oxide, and less frequently Cu minerals, as single fragments. We present new field-based measurements data of the geochemistry of gas/water from fumaroles and acid crater lakes, and fall deposit analysis, that integrated with the eruptive record and GOES satellite data, suggests that the eruptive period 2010-2011 has been related to an increasing of heat and mass transfer from hydrothermal-magmatic reservoirs, which would have been favoured by the formation and/or reactivation of cracks after 8.8 Mw Maule earthquake in February 2010. This process also allowed the ascent of fluids from a shallow hydrothermal source, dominated by reduced species as H 2 S and CH 4 , during the entire eruptive period, and the release of more oxidizing fluids from a deep magmatic reservoir, dominated by acid species as SO 2 , HCl and HF, increasing strongly after the end of the eruptive period, probably since October 2011. The eruptive period was scored with a magnitude of 3.36, corresponding to a VEI 1-2.
In the Spratly Islands (Truong Sa Islands) and adjacent areas, volcanic activities are quite strong after the sea-floor spreading in the Cenozoic Era. However, it is difficult to define their ranges and spatial locations. Based on the... more
In the Spratly Islands (Truong Sa Islands) and adjacent areas, volcanic activities are quite strong after the sea-floor spreading in the Cenozoic Era. However, it is difficult to define their ranges and spatial locations. Based on the different characteristic between eruptive volcanic basalt and sedimentary rocks near the surface, it can be said that, the blocks which are higher density and magnetization than those surroundings could be identified as eruptive volcanic basalt. This paper presents the methods of reduction to the magnetic equator in low latitudes to bring out a better correlation between magnetic anomalies and their causing-sources; High-frequency filtering is to separate gravity and magnetic anomalies as well as information about the volcanic basalts in the upper part of the Earth's crust; 3D total gradient is to define the spatial location of high density and magnetic bodies. The potential structures of eruptive volcanic basalt are predictively determined by multi-dimensional correlation analysis between high-frequency gravity and magnetic anomalies with weighted total gradient 3D. The results from the above-mentioned methods have shown that the distribution of the eruptive volcanic basalt mainly concentrates along the Spratly Island's seafloor-spreading axis, transitional crust, Manila trench and some large fault zones. These results are improved by available seismic data in the study area. Keyword: Spratly Islands, Reduction to the equator, 3D total gradient, Eruptive volcanic basalt.
Eruption source parameters (ESP) characterizing volcanic eruption plumes are crucial inputs for atmospheric tephra dispersal models, used for hazard assessment and risk mitigation. We present FPLUME-1.0, a steady-state 1-D... more
Eruption source parameters (ESP) characterizing volcanic eruption plumes are crucial inputs for atmospheric tephra dispersal models, used for hazard assessment and risk mitigation. We present FPLUME-1.0, a steady-state 1-D (one-dimensional) cross-section-averaged eruption column model based on the buoyant plume theory (BPT). The model accounts for plume bending by wind, entrainment of ambient moisture, effects of water phase changes, particle fallout and re-entrainment, a new parameterization for the air entrain- ment coefficients and a model for wet aggregation of ash par- ticles in the presence of liquid water or ice. In the occurrence of wet aggregation, the model predicts an effective grain size distribution depleted in fines with respect to that erupted at the vent. Given a wind profile, the model can be used to deter- mine the column height from the eruption mass flow rate or vice versa. The ultimate goal is to improve ash cloud disper- sal forecasts by better constraining the ESP (column height, eruption rate and vertical distribution of mass) and the effec- tive particle grain size distribution resulting from eventual wet aggregation within the plume. As test cases we apply the model to the eruptive phase-B of the 4 April 1982 El Chichón volcano eruption (México) and the 6 May 2010 Eyjafjalla- jökull eruption phase (Iceland). The modular structure of the code facilitates the implementation in the future code ver- sions of more quantitative ash aggregation parameterization as further observations and experiment data will be available for better constraining ash aggregation processes.
Height of plumes generated during explosive volcanic eruptions is commonly used to estimate the associated eruption intensity (i.e., mass eruption rate; MER). In order to quantify the relationship between plume height and MER, we... more
Height of plumes generated during explosive volcanic eruptions is commonly used to estimate the associated eruption intensity (i.e., mass eruption rate; MER). In order to quantify the relationship between plume height and MER, we performed a parametric study using a three-dimensional (3D) numerical model of volcanic plumes for different vent sizes. The results of five simulations indicate that the flow pattern in the lower region of the plume systematically changes with vent size, and hence, with MER. For MERs b 4 × 10 7 kg s −1 , the flow in the lower region has a jet-like structure (the jet-like regime). For MERs N10 8 kg s −1 , the flow shows a fountain-like structure (the fountain-like regime). The flow pattern of plumes with 4 × 10 7 kg s −1 b MERs b 10 8 kg s −1 shows transitional features between the two flow regimes. Within each of the two flow regimes, the plume height increases as the MER increases, whereas plume heights remain almost constant or even decrease as MER increases in the transitional regime; as a result, the jet-like and fountain-like regimes show distinct relationships of plume height and MER. The different relationships between the two regimes reflect the fact that the efficiency of entrainment of ambient air in the jet-like regime is substantially lower than that in the fountain-like regime. It is suggested that, in order to estimate eruption intensity from the observed plume heights, it is necessary to take the different flow regimes depending on MER into account.
We carry out a parametric study in order to identify and quantify the effects of uncertainties on pivotal parameters controlling the dynamics of volcanic plumes. The study builds upon numerical simulations using FPLUME, an integral... more
We carry out a parametric study in order to identify and quantify the effects of uncertainties on pivotal parameters controlling the dynamics of volcanic plumes. The study builds upon numerical simulations using FPLUME, an integral steady-state model based on the Buoyant Plume Theory generalized in order to account for volcanic processes (particle fallout and re-entrainment, water phase changes, effects of wind, etc). As reference cases for strong and weak plumes, we consider the cases defined during the IAVCEI Commission on tephra hazard modeling inter-comparison study (Costa et al., 2016). The parametric study quantifies the effect of typical uncertainties on total mass eruption rate, column height, mixture exit velocity, temperature and water content, and particle size. Moreover, a sensitivity study investigates the role of wind entrainment and intensity, atmospheric humidity, water phase changes, and particle fallout and re-entrainment. Results show that the leading-order parameters that control plume height are the mass eruption rate and the air entrainment coefficient, especially for weak plumes.
Planchón-Peteroa volcano started a renewed eruptive period between January 2010 and July 2011. This eruptive period was characterized by the occurrence of 4 explosive eruptive phases, dominated by low-intensity phreatic activity, which... more
Planchón-Peteroa volcano started a renewed eruptive period between January 2010 and July 2011. This eruptive period was characterized by the occurrence of 4 explosive eruptive phases, dominated by low-intensity phreatic activity, which produced almost permanent gas/steam columns (200-800 m height over the active crater). Those columns presented frequently scarce ash, and were interrupted by phreatic explosions that produced ash columns 1,000-3,000 m height in the more intense periods. Eruptive plumes were transported in several directions (NW, N, NE, E and SE), but more than half of the time the plume axis was 130-150° E, and reached a distance up to 638 km from the active crater. Tephra fall deposits identified in the NW, N, NE, E and SE flanks covered an area of 1,265 km 2 , thickness variable from 4 m (SE border of active crater) to ~0.5 cm 36.8 km SE and ~8 km NW from active crater, respectively, corresponding to a minimum volume of 0.0088 km 3. Tephra fall deposit is exclusivel...
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