Displays

At large crystal contents magma exhibits non-Newtonian behavior, typically shear thinning due to crystal orientation along streamlines. 1D models widely used for extrusive eruption simulations cannot capture efficiently the complexity of cross-conduit variations of the properties of magmas as they assume parabolic velocity profile and averaged properties of magma. Large aspect ratios of volcanic conduits (length/diameter) makes use of fully 2D numerical models computationally expensive and not reliable because of extremely large cross-conduit variation of parameters.

Here we present results of numerical simulations of a quasi-2D model that accounts for magma crystallization with the release of the latent heat, shear thinning rheology, heat transfer and viscous dissipation. Simulated velocity profile is far from parabolic. Shear layers form initially near the wall of the conduit and migrate towards the interior as magma ascends. Shear heating results in significant increases in temperature of the magma in narrow shear bands. There is a drastic difference between the predictions of 1D and quasi-2D models in terms of pressure-discharge rate relations. Lava dome morphology can be strongly affected by the formation of shear zones inside volcanic conduits during magma ascent.

How to cite: Melnik, O. and Tsvetkova, Y.: Shear localization during magma ascent: results from quasi-2D numerical simulations , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3284, https://doi.org/10.5194/egusphere-egu2020-3284, 2020.

Measurements abound for the permeability of volcanic rocks, high temperature magmas, synthetic analogues for magma and rock, and 3-dimensional domains of porous media simulated numerically. Despite a wealth of data, the dominant approach to parameterisation has been empirical, and scarcely goes beyond the power-law models for percolating systems. Here we propose a suite of methods to bring the data for these complex systems in line with theoretically grounded percolation models. To do this we create numerical samples using variations on theme of overlapping spheres filling volumes. In order to create a wide range of possible geometries, we can either define the spheres as the pore phase, or the inter-sphere volume as the pore phase, such that one option is the inverse of the other. In either case, we simulate fluid flow through the pore phase until steady state, to determine the Darcian and inertial permeability tensors. We compare these results with derived, fully theoretical percolation theory and find good agreement without fitting parameters. In order to render this useful for understanding permeability in volcanic scenarios, we compare these validated models to a large database of compiled published permeability data. This approach allows us to group the permeability of magmas into three universality classes, which each have just one dimensionless solution: (1) initially granular magmas, such as variably welded ignimbrites or tuffisites, and (2) bubbly magmas, such as pumice.

How to cite: Vasseur, J., Wadsworth, F., and Dingwell, D.: Beyond empiricism: Quantitative models for the permeability of heterogeneous magmas, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9497, https://doi.org/10.5194/egusphere-egu2020-9497, 2020.

The rheology and strength of bubbly magma govern eruption dynamics by determining the possibility of fragmentation of ascending magmas. The rheology of magma also regulates the propagation velocity and attenuation of seismic waves, and are required parameters for understanding seismic monitoring. We measured the rheology and strength of high porosity (>0.86) rhyolitic magma at 500-950 degrees C. The measured shear modulus and strength are several orders of magnitude lower than bubble-free rhyolite melt, implying that high porosity magma cannot avoid fracturing during magma ascent. The occurrence of fractures is observed in the low-temperature magma (<800 degrees C). In this temperature range, the measured attenuation is low (Q>1). That is, the elastic energy originated by deformations avoids attenuation and is stored in the bubbly magma to cause fracturing. The newly found porosity-dependent strength based on our measurements comprehensively explains three different fragmentation criteria that have been previously proposed independently. Our measurements also show that the shear modulus becomes lower by increasing porosity, which can slow the shear wave velocity. These results suggest that knowing the attenuation of the seismic wave is useful to evaluate magma temperature and the possibility of a fragmentation event that may determine subsequent volcanic activities.

Reference: Namiki et al. Journal of Volcanology and Geothermal Research (2020).

How to cite: Namiki, A., Tanaka, Y., Okumura, S., Sasaki, O., Sano, K., and Takeuchi, S.: Fragility and an extremely low shear modulus of high porosity silicic magma, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2535, https://doi.org/10.5194/egusphere-egu2020-2535, 2020.

Magma degassing dynamics play an important role controlling the explosivity of volcanic eruptions. Some of the largest explosive eruptions in history have been fed by silica-rich magmas in volcanic systems with complex dynamics of volatiles degassing. Degassing of magmatic water drives bubble nucleation and growth, which in turn increases magma buoyancy and results in magma ascent and an eventual eruption. While micro- to milli-meter sized crystals are known to cause heterogeneous bubble nucleation and to facilitate bubble coalescence, the effects of nanolites remains mostly unexplored. Nanolites have been hypothesized to be a primary control on the eruptive style of silicic volcanoes, however the mechanisms behind this control remains unclear.

Here we use an experimental approach to show how nanolites dramatically increase the bubble number density in a degassing silicic magma compared to the same magma without nanolites. The experiments were conducted using both nanolite-free and nanolite-bearing rhyolitic glass with different low initial water content. Using an Optical Dilatometer at 1 bar ambient pressure, cylindrical samples were heated at variable rates (1-30 °C min^-1) to final temperatures of 820-1000 °C. This method allowed us to continuously monitor the volume, and hence porosity evolution in time. X-ray computed microtomography (µCT) and Scanning Electron Microscope (SEM) analyses revealed low and high bubble number densities for the nanolite-free and nanolite-bearing samples respectively.

Comparing vesicle number densities of natural volcanic rocks from explosive eruptions and our experimental results, we speculate that some very high naturally occurring bubble number densities could be associated with nanolites. We use a magma ascent model with P-T-H₂O starting conditions relevant for known silicic eruptions to further underpin that such an increase in bubble number density caused driven by the presence of nanolites can feasibly turn an effusive eruption to an eventually explosive behavior.

How to cite: Cáceres, F., Wadsworth, F., Scheu, B., Colombier, M., Madonna, C., Cimarelli, C., Hess, K.-U., Kaliwoda, M., Ruthensteiner, B., and Dingwell, D. B.: The effect of nanolites on degassing of silica-rich magma, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17732, https://doi.org/10.5194/egusphere-egu2020-17732, 2020.

Very long period (VLP) seismic signals observed in volcanic environments are thought to be produced by magma and gas flow through conduits. Stromboli Volcano, Italy, typically produces hundreds of VLPs per day. These have been generally attributed to the flow of gas slugs through the shallow plumbing system and thus linked to the mechanism thought to drive Strombolian explosions. During a 6-day-long seismo-acoustic campaign in May 2018 (a period characterized by relatively low activity) we recorded 1900+ seismic events, the majority of which have significant energy in the VLP (2-100 s) band. We used a coincident STA/LTA trigger to identify seismic events in continuous waveform data and then used the PeakMatch algorithm (Rodgers et al., 2015) to identify seismic multiplets, with a focus on VLPs. To identify explosions, we applied the same coincident trigger to infrasound data, and manually identified gas jetting events using spectrograms and high-pass-filtered (20 Hz) waveforms. 

We identified ~250 explosions and ~600 jetting events. Seismic multiplet analysis identified two main families of repeating events. Family 1 (F1) has over 500 events and Family 2 (F2) has over 150 events based on a 0.7 correlation threshold. We find that F1 VLPs coincide in time with ~6% of explosions and ~0.8% of jetting events and F2 VLPs coincide in time with ~28% of explosions and ~2.7% of jetting events (we term these “silent VLPs”). These VLPs do not correspond with lava effusion (Marchetti and Ripepe, 2005; Ripepe et al., 2015). F2 have a higher dominant period (8-10 s) compared to F1 (3-4 s). The repeating VLPs are part of a broadband signal and the higher frequencies start after the VLP. VLP peak amplitudes are generally larger for F1 events. The dip of the VLP particle motion roughly locates the F1 and F2 VLP source centroids beneath the active crater and are stable throughout the dataset. Both VLP displacements show a small outward, large inward, and subsequent large outward motion from the crater. The lack of explosions relative to repeating VLPs does not support the slug model, where a slug rises through a conduit, generates a VLP through interactions with changes in conduit geometry, and then bursts at the lava free surface. Our observations support the plug model (Suckale et al., 2016). We suggest the “silent” VLPs are generated when the gas bubbles interact with and move into the semipermeable plug. Then the plug behaves as a mechanical filter for gas escape and allows for passive and explosive escape mechanisms.

How to cite: McKee, K., Roman, D., Fee, D., Waite, G., and Ripepe, M.: Silent VLPs At Stromboli: Implications For Slug Vs. Plug, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2769, https://doi.org/10.5194/egusphere-egu2020-2769, 2020.

Basaltic eruptions are the most common form of volcanism on Earth and planetary bodies. The low viscosity of basaltic magmas generally favours effusive and mildly explosive volcanic activity. Highly explosive basaltic eruptions occur less frequently and their eruption mechanism still remains subject to debate, with implications for the significant hazard associated with explosive basaltic volcanism. Particularly, highly explosive eruptions require magma fragmentation, yet it is unclear how basaltic magmas can reach the fragmentation threshold.

In volcanic conduits, the crystallisation kinetics of an ascending magma are driven by degassing and cooling. So far, the crystallisation kinetics of magmas have been estimated through ex situ crystallization experiments. However, this experimental approach induces underestimation of crystallization kinetics in silicate melts. The   crystallization experiments reported in this study were performed in situ at Diamond Light Source (experiment EE12392 at the I12 beamline), Harwell, UK, using basalt from the 2001 Etna eruption as the starting material. We combined a bespoke high-temperature environmental cell with fast synchrotron X-ray microtomography to image the evolution of crystallization in real time. After 4 hours at sub-liquidus conditions (1170 °C and 1150 °C) the system was perturbed through a rapid cooling (0.4 °C/s), inducing a sudden increase of undercooling. Our study reports the first in situ observation of exceptionally rapid plagioclase and clinopyroxene crystallisation in trachybasaltic magmas. We combine these constraints on crystallisation kinetics and viscosity evolution with a numerical conduit model to show that exceptionally rapid syn-eruptive crystallisation is the fundamental process required to trigger basaltic magma fragmentation under high strain rates. Our in situ experimental and natural observations combined with a numerical conduit model allow us to conclude that pre-eruptive temperatures <1,100°C can promote highly explosive basaltic eruptions, such as Plinian volcanism, in which fragmentation is induced by fast syn-eruptive crystal growth under high undercooling and high decompression rates. This implies that all basaltic systems on Earth have the potential to produce powerful explosive eruptions.

How to cite: Arzilli, F., La Spina, G., Burton, M. R., Polacci, M., Le Gall, N., Hartley, M. E., Di Genova, D., Cai, B., Vo, N. T., Bamber, E. C., Nonni, S., Atwood, R., Llewellin, E. W., Brooker, R. A., Mader, H. M., and Lee, P. D.: Highly explosive basaltic eruptions: magma fragmentation induced by rapid crystallisation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8046, https://doi.org/10.5194/egusphere-egu2020-8046, 2020.

Most volcanic ash produced during explosive volcanic eruptions sediments as aggregates of various types that typically have a greater fall velocity than the particles of which they are composed. As a result, aggregation processes are commonly known to affect the sedimentation of fine ash by considerably reducing its residence time in the atmosphere. Nonetheless, speculations also exist in the literature that aggregation does not always result in a premature sedimentation of their constitute particles but that it can also result in a delayed sedimentation (i.e. the so-called rafting effect). However, previous studies have considered rafting as a highly improbable phenomenon due to a biased representation of aggregate shapes.

Here we provide the first theoretical evidence that rafting may not only occur, but it is probably more common than previously thought, helping to elucidate often unexplained field observations. Starting from field evidence of rafted aggregates at Sakurajima Volcano (Japan), we clarify the conditions for which aggregation of volcanic ash results either in a premature or a delayed sedimentation.

Moreover, using the Lagrangian dispersion model NAME, we show the practical consequences of rafting on the final sedimentation distance of aggregates with different morphological features. As an application we chose the case study of the 2010 eruption of Eyjafjallajökull volcano (Iceland), for which rafting can increase the travel distances of ash <500 m up 3.7 times with respect to sedimentation of individual particles.

These findings have fundamental implications both for real-time forecasting and long-term hazard assessment of volcanic ash dispersal and sedimentation and for weather modelling. The constraints on rafting presented and discussed in this work will help the scientific community to clarify the often unexpected role of aggregation in creating a delayed sedimentation of coarse ash.

How to cite: Rossi, E., Beckett, F., Bonadonna, C., and Bagheri, G.: The fate of volcanic ash aggregates: premature or delayed sedimentation?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5278, https://doi.org/10.5194/egusphere-egu2020-5278, 2020.

Tube pumice is characterized by aligned highly elongated bubbles and is a common product of explosive silicic eruptions. The relative abundance of tube pumice and non-tube pumice in the stratigraphy has been interpreted as resulting from temporal and spatial variations in a conduit flow. Therefore, understanding the formation mechanism of tube pumice is valuable, but still debated. Most previous studies interpret tube pumice forming from simple shear deformation, assuming a parabolic velocity profile across a conduit. However, simple shear cannot explain the observation that tube pumice is rare in plinian falls but frequent in ignimbrites (interpreted to have wider vents).

In this study, we combine a bubble deformation model with a quasi-two-dimensional steady conduit flow model. A bubble is deformed by the velocity gradient while moving within the conduit flow. The conduit flow model is calculated for the 1.8 ka Taupo plinian eruption, which produced a high proportion of tube pumice in the ignimbrite phase. In this abstract, we explain results from two rheological models showing distinct velocity profiles. In the Newtonian isothermal fluid, the velocity profile across the conduit becomes parabolic. In a fluid that allows viscous heating, the temperature near the conduit wall rises up sharply, leading to a strong reduction in viscosity, and the velocity profile changes from a parabolic shape to a plug-like shape. The parabolic velocity profile produces highly elongated bubbles mainly by simple shear, while the plug-like velocity profile is dominated by pure shear and accumulates less strain to elongate bubbles. The bubble shape at the fragmentation surface depends significantly on the velocity profile and its change along the conduit.

We also conduct a quantitative and statistical bubble shape analysis of pumice erupted at Taupo volcano. It shows that the plinian pumices have a single peak in the bubble shape distribution, while the ignimbrite pumices have a broad distribution and contain highly elongated bubbles. The comparison of the distribution of pumice textures with the simulation results suggests that the velocity profile of the plinian phase is close to a plug-like shape. We also calculate bubble deformation for the Taupo ignimbrite eruption, using the viscous-heating model. We model a　wider conduit for the ignimbrite phase which leads to lower shear rate around the conduit walls and a higher proportion of the conduit experiencing parabolic flow compared to the plinian phase. This increased proportion of parabolic velocity profile in the conduit can explain a large number of tube pumice in the Taupo ignimbrite.

How to cite: Ohashi, M., Ichihara, M., Maeno, F., Kennedy, B., and Gravley, D.: Numerical simulation of bubble deformation in various velocity profiles across a conduit, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12279, https://doi.org/10.5194/egusphere-egu2020-12279, 2020.

The geodynamical side of explosive volcanic eruption modelling on the one hand, as well as the petrological one on the other, have reached a high degree of sophistication and maturity independently from each other over the years. Unfortunately, adherents of one discipline often only utilize the other’s tools in a simplified and makeshift way, obscuring the full potential of their synergies. Over the past decade efforts have been made to re-integrate both approaches to the issue into a more holistic view on the sub-surface processes leading to and concurrent with explosive volcanism.
One of the difficulties encountered in that effort are conceptual and technical incompatibilities between thermo- and fluid-dynamic modelling toolboxes. While the tools perform well individually, they are often not suitable to work in combination in highly complex numerical models, due to interface problems impeding performance.
For an ongoing numerical study on transport processes within a volcanic conduit, it has been deemed necessary to re-implement an established thermodynamic model based on Holland and Powell (2011, and follow-ups) in order to a) attain the required computing performance and b) to gain sufficient petrological insight (starting from a geophysical point of view) to be able to make apt use of the tool then at hand.
The path to the intermediate goal of deriving the thermodynamic and transport properties (e.g. density, viscosity, heat capacity and conductivity) in a self-consistent and stable manner suitable for further use in a numerical fluid-dynamics model is illustrated here. The focus is on problems encountered with the petrological modelling, and on the subsequent derivation of the above properties, that are not directly available from the former results. The methods presented are general and applicable to various settings regarding volcanic chemistry and transport processes, however, they will be demonstrated on low-viscosity open-conduit systems typical for strombolian activity.

How to cite: von der Lieth, J. and Hort, M.: Towards a self-consistent thermodynamic magmatic model for conduit transport processes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7602, https://doi.org/10.5194/egusphere-egu2020-7602, 2020.

The paroxysmal eruptions of Stromboli in July and August 2019 highlighted with stark clarity the risks associated with visiting the summit of this remarkable volcano. It is an imperative for the volcanological community to recognise signals which precede such paroxysms, with the aim of maximising the warning time before an eruption. The common interpretation of the process driving paroxysms is that a volume of buoyant magma rises from depth, degassing in closed-system. The ascent is rapid, from 10 km depth to the surface in a few hours. This rapid ascent produces a kinetic limit to crystal growth, reflected in the ‘blonde’ colour of the eruption products. Closed-system degassing leads to an overpressure in the rising slug, which helps lift magma in the conduit, pressurising also the shallow system.

The gas plume produced by the 28 August 2019 eruption was observed approximately 2 hours after eruption by the orbiting TROPOMI imaging spectrometer aboard Sentinel-5P. Using the Plume Trajectory modelling approach, we have reconstructed a time series of SO₂ flux associated with the explosion.  This reveals no clear precursor in SO₂ emissions, but our temporal resolution is limited to 20-30 minutes. A total SO₂ mass of 360 tonnes was quantified.

We can use this SO₂ mass together with previously measured gas compositions of explosive gas emissions to quantify the total mass of gas at explosion and an estimate of the magma mass required to produce this SO₂ mass. Together, these provide the initial conditions required to apply a magma ascent model in which we calculate the overpressure of the slug during its ascent. This provides a basis for determining the shallow deformation produced by both the increase in magma level and over-pressurised gas slug, and this may be helpful in constraining the timescales of precursory deformation.

How to cite: Burton, M., Hayer, C., and La Spina, G.: Constraints on magma ascent and pressurisation prior to explosive paroxysms on Stromboli, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22139, https://doi.org/10.5194/egusphere-egu2020-22139, 2020.

Several types of lava dome morphology can be distinguished depending on the flow rate and the rheology of magma. At an endogenous regime, magma is embedded inside the dome and fresh magma is not extruded on the surface; vice versa, at an exogenous regime, a fresh lava is extruded, and a lava obelisk is of particular interest. Sometimes obelisks reach hundreds of meters in height before they collapse. We present models of magma extrusion on the surface and lava dome evolution to analyze morphology of the domes. For this aim, we consider a flow of a Newtonian and non-Newtonian viscous inhomogeneous incompressible fluid in the field of gravity. The flow is described by the Navier-Stokes equations, the continuity equation, the transport equation of a two-component incompressible fluid, the heat conduction equation, and the rheological law. The lava viscosity in our models depends on the crystals concentration, temperature, and the rate of shear deformation. We show that the morphology of the domes depends on the characteristic time of crystal growths in the magma and on the rate of magma extrusion. In this case, obelisks are formed at a small value of the characteristic time of growth of crystals and/or low extrusion rates. At high values of the characteristic time and high extrusion rates, magma spreads over the surface after an eruption.

How to cite: Ismail-Zadeh, A., Melnik, O., and Tsepelev, I.: Morphology of lava domes inferred from numerical modeling , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1962, https://doi.org/10.5194/egusphere-egu2020-1962, 2020.

Mt. Pelée is a historically active stratovolcano, situated on the island of Martinique in the French Caribbean.  It exhibits a variety of eruptive styles, from dome formation to highly violent explosivity. 

In 1902, a Pelean event destroyed the town of St. Pierre, killing more than 28,000 residents (Lacroix, 1904).  As this town is now re-established, along with several others along the volcano’s flanks, it is of utmost importance to understand the range of eruptive activity possible such that preparedness of the local authorities and population can be improved.

There remains a gap in quantitative understanding of the energy required to fragment material to produce explosive eruptions, as this process is not directly observable.  Further, eruption records are incomplete (as at most volcanic islands) due to product loss to the ocean and intense tropical erosion.  Here, we constrain the energies of past eruptions by performing rapid decompression experiments and comparing the resulting grain-size distributions with primary deposits and dispersal in the field.

During a field campaign in March 2019, we collected ash and pumice blocks from five recent magmatic eruptions.  Two of these eruptions are historic (the Pelean episodes of 1902-1905, and 1929-1932), and three are prehistoric (the Plinian eruptions of 1300 CE P1, 280 CE P2, and 79 CE P3)(Carazzo et al. 2012).  We characterized ash (morphology), and constrained petrophysical (porosity, density, and permeability) and thermal properties of cylindrical samples. These cores (58-70% porosity) were subjected to rapid decompression in shock tube experiments to mimic explosive eruptions.  Fragmentation efficiency results from a combination of material properties and experimental conditions (temperature and overpressure). The particulate products were evaluated for their grain-size distribution in order to calculate the fractal dimension D_f and constrain eruptive conditions.

Our results provide new insights into the energy required for magma fragmentation at Mt. Pelée and similar volcanoes. We hope to elucidate whether the 1902 eruption was catastrophic due to significant and measurable differences in eruption dynamics, or due to the flank topography and direction of the initial blast. 

References:

Carazzo, G., Tait, S., Kaminski, E., Gardner, E., (2012), The recent Plinian explosive activity of Mt. Pelée volcano (Lesser Antilles): The P1 AD 1300 eruption, Bull. Volc., 74, 2187-2203, doi: 10.1007/s00445-012-0655-4

Lacroix, A. (1904) La Montagne Pelée et ses éruptions. Masson, Paris

How to cite: Huebsch, M., Kueppers, U., Carazzo, G., Lejeune, A.-M., Michaud-Dubuy, A., Hess, K.-U., and Dingwell, D. B.: Pyroclast textures and fragmentation efficiency - constraining the range of eruptive dynamics of Mt. Pelée volcano, Martinique, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17813, https://doi.org/10.5194/egusphere-egu2020-17813, 2020.

La Joya de Yuriria maar volcano and La Sanabria-San Roque tuff ring complex manifests at the southern and northern extreme of the NNW-SSE trending clusters of phreatomagmatic vents of Valle de Santiago volcanic field, which forms the NE part of the famous Michoacan-Guanajuato Volcanic Field ( (MGVF), central Mexico. La Sanabria-San Roque complex is located in the south of the town of Irapuato and is composed of three tuff rings namely San Joaquin (SJ), La Sanabria (LS) and San Roque (SR). Their tephra deposits were studied at 7 different active quarries, which suggests that the San Joaquin tuff ring was formed before La Sanabria-San Roque tuff ring complex. San Joaquin is composed of medium-size lapilli flow (Mdphi=-2.05 to -3.90, σphi=2.00 to 2.58) and fine ash surge units and contains different types of lithics and juvenile fragments (50-68 vol.%.). About four types of lithics were identified namely: grey-colored vesicular basaltic andesites (9-27 vol.%), grey-colored non-vesicular basaltic andesites (17-19 vol.%), white lithics (sediments 0-1 vol.%), red-colored lithics (volcanic breccias 1-3 wt.%) along with few plagioclase crystals (0.54-0.66 vol.%) that are exposed at quarries 1, 3. La Sanabria-San Roque tuff ring complex tephra deposits are exposed at quarries 2, 5 and 8 and are composed of intercalated flow (Mdphi=-1.65 to -2.15, σphi=1.00-1.83) and fallout (Mdphi=-2.00 to -6.10, σphi=2.00) units with juvenile content from 41-87 vol.% and four different types of lithic fragments: grey-colored vesicular lithics (1- 20 vol.%), grey-colored compact lithics (2-6 vol.%), which is considerably lower than the amount encountered within SJ deposits. Further-more, white-colored lithics, mostly sediments (0-10 vol.%) and red-colored lithics (rhyolites and/or volcanic breccias) around 0-3 vol.%.

La Joya de Yuriria is currently located on the southern margin of the artificial lake of Yuriria and its tephra sequence is composed of mostly fallout units (Mdφ=-4.45 to -4.60, σφ=1.88 to 2.55), followed by flow units (Mdφ=-2.95 to -3.800, σφ=1.93 to 2.05) that are separated with both indurated, fine-ash wet and dry surge units of which a very particular fine-ash dry surge unit ( Mdφ=-0.95, σφ=2.03), yellowish in color (due to oxidation?), may represent a short-term break within the phreatomagmatic activity. It is also composed of flow units (Mdφ=-1.50 to -2.95, σφ=1.40 to 3.43) that are clast supported, friable and contains medium to coarse lapilli size fragments that are rich in accidental lithics with very juvenile clasts (<33 vol.%) of basaltic andesite (SiO₂= 54.4 wt%, Na₂O+K₂O= 5.21 wt%) with very few juvenile content (5-37 wt.%), except at VS-1741-P7 (85 vol.%) and abundance of light grey colored angular lithics that were classified as vesicular (4.51 vol.%) and non-vesicular (1-66 vol.%) with few reworked lithics (1-5 vol.%) and altered lithics (1-5 vol.%).

Vesicularity index on 2741 juvenile clasts from these vents was utilized to determine the magma fragmentation and the timing of magma-water interactions (especially exsolution of volatiles before or during mag-water interaction). To corroborate this, Bubble Nucleation Density and crystal texture of primary vesicles within glass shards were also performed to validate the interpretations made.

How to cite: Campos Domínguez, A. J., Kshirsagar, P., Puy y Alquiza, M. D. J., and Miranda Aviles, R.: Magma fragmentation and timing of water-magma interaction of La Joya de Yuriria maar volcano and La Sanabria-San Roque tuff ring complex, Mexico, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20546, https://doi.org/10.5194/egusphere-egu2020-20546, 2020.

The Teide-Pico Viejo (PT-PV) stratovolcanoes constitute one of the major potentially active volcanic complexes in Europe. PT-PV was traditionally considered as non-explosive system however, recent studies (ie. García et al. 2014) have pointed out that the explosive character of phonolitic magmas, including plinian and subplinian eruptions and generation of pyroclastic density currents, have also been significant within the last 30 kyr volcanological record. This explosive activity is mostly associated to satellite dome vents, like the one studied in this work, Pico Cabras. Dome-forming eruptions usually present sudden transitions between explosive and effusive activity. A better knowledge of this type of eruptions and about the main mechanisms controlling the changes in eruptive dynamics is required to undertake a comprehensive volcanic hazard assessment of Tenerife Island. In this study, we conduct a petrological and mineral characterization of the different eruption phases of Pico Cabras (pumice and lava flow samples for the explosive and effusive activity, respectively) with the aim of determining the factors that control these changes in the volcanic activity. Products were characterized with Scanning Electrom Microscope, and mineral phases, glass and volatile species (F, Cl) were analysed with electron microprobe and micro-XRF. The pre-eruptive conditions of the magma (pressure, temperature and water dissolved in the magma) were determined first by using available geothermobarometers, geohygrometers (Masotta et al., 2013; Mollo et al., 2015) and compared to those retrieved by using available phase equilibria experiments from the literature (ie. Andújar and Scaillet, 2012).

Our results suggest the presence of a compositionally stratified magma chamber at 1 kbar±0.5kbar prior to Pico Cabras eruption in which the differences in the eruptive styles are controlled by the temperature and the amount of volatiles dissolved in the melt. The explosive phase is related to the upper part of the magma chamber at 725ºC±25ºC and 3,5-5 wt% H₂O and the effusive phase with the main body of the chamber at 880ºC±30ºC and 2,5-3 wt% H₂O. Feldspar zonations show that overturn events occurred in the different layers of the magma chambers (“self-mixing”) and suggest that the eruption was triggered by underplating of mafic magma without magma mixing. Chemical composition of some feldspars from the explosive phase are equivalent to those found in El Abrigo eruption, the last caldera-forming episode (ca. 190 ka), demonstrating that PT-PV volcanic system is still capable of producing evolved and very explosive magmas.

This research has been partially funded by a CSIC JaeIntro grant and the EC Grant EVE (DG ECHO Ref: 826292).

How to cite: Dorado, O., Andújar, J., Martí, J., and Geyer, A.: Mechanisms controlling explosive-effusive transition of Teide-Pico Viejo complex dome eruptions. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-199, https://doi.org/10.5194/egusphere-egu2020-199, 2020.

The Caviahue-Copahue Volcanic Complex (CCVC, Argentina) composes one of the most active volcanic centers in the Southern Volcanic Zone (SVZ) of the Andes, characterized by the presence of voluminous explosive and effusive deposits. Despite its young age (< 5 Ma), CVCC deposits were strongly affected by two glaciations, leading to the removal of a considerable volume of the original deposits, requiring alternative techniques for the reconstruction of this volcanic center. The Riscos Bayos Ignimbrites (RBI) consist of a sequence of non-welded ignimbrites, located approximately 15 km southeast of the CVCC. This unit is commonly associated with the putative collapse of Caviahue caldera (15 x 20 km, 1 km deep) during the Pleistocene, although the source area and emplacement conditions of RBI still poorly constrained. In this work, we combine fieldwork, anisotropy of magnetic susceptibility (AMS, 23 sites) and rheological analyses (17 samples) in order to trace RBI source region and constrain its emplacement conditions, addressing its relevance to CVCC evolution. Rheological parameters, including viscosity, glass transition temperature, and liquidus temperatures were obtained using numerical models available from the literature, while AMS samples were measured using a Kappabridge MFK1-A (Agico) and the data processed using Anisoft5 (Agico). The magnetic mineralogy was characterized using several experiments, including isothermal remanet magnetization, thermomagnetic curves, hysteresis loops, first-order reversal curves and scanning electron microscopy. Our data indicate liquidus temperatures ranging from 969 to 1100 ºC, glass transition temperatures from 653 to 721 ºC, and viscosity (at liquidus temperature) from 3.4 to 7.3 log Pa.s. The absence of welding features in the samples implies RBI emplacement at temperatures below the glass transition temperature, suggesting a fast and effective cooling of the pyroclasts before their settling. The low crystal content of the samples suggests eruption temperatures close to the calculated liquidus temperature of the melt.  AMS directional analyses indicate a consistent transport sense to SSE (Az of approximately 100º), implying the southern rim of the CVCC as the main source region of RBI. Magnetic experiments show primary, multi-domain, high curie temperature (580 ºC) titanomagnetites as the main carriers of the AMS signal. Most ellipsoids display oblate to triaxial geometry, with a low degree of anisotropy (< 5%) and magnetic susceptibility (1.0 x 10^-2 SI). The low welding degree of RBI units and its geographic distribution outside the Caviahue depression contributes to the Caviahue caldera hypothesis in the region, suggesting its emplacement as an ‘extra-caldera’ pyroclastic unit.

How to cite: Haag, M., Moncinhatto, T., Sommer, C., Savian, J., Caselli, A., Trindade, R., Hartmann, G., and Poletti, W.: Source area and emplacement conditions of Riscos Bayos Ignimbrites, Caviahue-Copahue Volcanic Complex (Argentina), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2704, https://doi.org/10.5194/egusphere-egu2020-2704, 2020.

Toba Caldera Complex, Indonesia is well known as the largest Quaternary caldera (87x33 km) that formed by four major eruptions among which the biggest one is the eruption of the Youngest Toba Tuff (YTT) about 74,000 years ago. Textural study of the pumice clast from YTT has been done to estimate the decompression rate by using bubble number density data. The result shows that decompression rate of Toba Caldera forming eruption varies in two order magnitude ranging from 10⁶ – 10⁸ Pa/s. Southern pumices show the lower value than pumices from northern caldera. Similarly, new data about lithic distributions and mineral components of YTT from the northern and southern caldera showed several different characteristics. This fact suggests possibility of different processes which is distinguish production of southern and northern deposits. Therefore, understanding both conduit and chamber processes is needed to reveal the origin of differences in deposits. This study aims to elucidate magma chamber condition by characterizing the deposit especially crystals from YTT eruption.

Characterizations of Toba Tuffs have been made but not been enough to discuss YTT in detail. In this study, we focus on spatial differences in YTT deposits. Samples from four different locations were employed for the analyses. Component analysis was carried out on components larger than 2 mm. Whole-rock geochemical data were obtained by XRF. Petrography analysis for 37 thin sections was conducted using optical microscope. Textural analysis was carried out for 84 free crystals and 25 selected thin sections using microphotographs taken by SEM and further analyzed using image processing software. Chemical analysis for free crystal was carried out by SEM-EDS, while for pumices grain of 22 thin sections was conducted using EPMA.

Geochemical data showed that YTT magma is rhyodacitic to rhyolitic in whole-rock compositions with wide range of SiO₂ (69.15–76.83 wt.%). There are differences in abundance and type of pumices, free crystals, and lithic in each location. Major minerals are plagioclase, biotite, sanidine, and quartz. Common characteristics of northern and southern part deposit is that most of crystals are fractured, some forming aggregates, has anhedral shape and wide variation in size (0.003 mm²-13.113 mm²). However, there are differences between northern and southern deposits: presence of amphibole with larger size, orange quartz, sieve texture, patchy zoning, oscillatory zoning, crystal clots, and wider range of anorthite (An₂₅– An₈₇) is mostly found in northern deposits.

Plagioclase composition from northern part shows bimodal distribution suggesting that crystallization does not occur simultaneously by single process. Furthermore, plots of anorthite number versus size and of average anorthite number versus crystal content show random distribution, suggesting the complex crystallization of plagioclase: other processes than fractional crystallization in magma chamber. Moreover, presence of antecryst and disequilibrium textures in northern deposit indicates intervention from older rocks or even other systems. Different characteristics between northern and southern deposits suggest that YTT deposits are generated by multiple eruptions from independent, at least two magma chambers.

Keywords: Toba Caldera, the Youngest Toba Tuff (YTT), Crystal Characterization, Conduit Process, Chamber Process, Fractional Crystallization, Multiple eruptions

How to cite: Bunga Naen, G. N. R., Toramaru, A., Miyamoto, T., and Wibowo, H. E.: The Youngest Toba Tuff (74 ka) Crystals Characterization, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6694, https://doi.org/10.5194/egusphere-egu2020-6694, 2020.

The emergence of the first organic molecules as a fundamental step in the prebiotic assembly of life remains enigmatic. Lightning has been considered as a potential energy source for the synthesis for first organic molecules. The iconic abiotic synthesis experiments: the discharge experiments performed in 1953 by Miller and Urey [1] under simulated reducing atmosphere conditions were conducted in the absence of any geomaterial substrate. Further, new views about the composition of the Early Earth’s atmosphere have been developed which require a revisiting of the Miller experiment.

Volcanic lightning associated with volcanism provides a possible energy source, a variety of different volcanic gases and possible catalysts to synthesize a variety of primitive organic molecules. Volcanic ash particles are known for their porosity, high surface area and significant surface reactivity. Volcanic plumes themselves provide a high variety of volcanic gases including, but not limited to reducing ones, and therefore may enlarge the spectrum for possibly available gas compositions in the Early Earth atmosphere.

Recent laboratory studies have successfully recreated near-vent volcanic lightning under laboratory conditions [2,3]. We will present first insights from volcanic discharge experiments under different atmospheric compositions, varying in CO₂, and N₂ composition to mimic some first Early Earth conditions. Special focus is given to the role of ash particles as a catalyst and container as well as the influence of gas composition on the yield of organic compounds.

[1] Miller, S.L. (1953). A production of amino acids under possible primitive earth conditions. Science, 117, 528-529.  

[2] Cimarelli, C., Alatorre-Ibargüengoitia, M.A., Kueppers, U., Scheu, B. and Dingwell, D.B. (2014). Experimental generation of volcanic lightening. Geology, 42, 79-82.

[3] Gaudin, D. and Cimarelli, C. (2019). The electrification of volcanic jets and controlling parameters: A laboratory study. EPSL, 513, 69-80.

How to cite: Springsklee, C., Steiner, T., Geisberger, T., Scheu, B., Huber, C., Eisenreich, W., Cimarelli, C., and Dingwell, D. B.: Prebiotic synthesis in volcanic discharges: lightning, porous ash and volcanic gas atmospheres, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8328, https://doi.org/10.5194/egusphere-egu2020-8328, 2020.

Glass-SO₂ reactions occurring at high temperatures in (terrestrial and extraterrestrial) volcanic environments have received increasing attention in the past years (e.g., Renggli and King 2018; Casas et al. 2019; Renggli et al. 2019), based on both natural and experimental observations. Laboratory studies carried out at high temperatures (>200 °C) demonstrate that volcanic glass in the presence of SO₂ reacts to form surficial sulfate-bearing minerals (e.g., Ayris et al. 2013; Delmelle et al. 2018), mostly calcium sulfate salts (CaSO₄). Thus, high temperature glass-SO₂ interaction acts as a sink for the magmatic S released during explosive volcanic activity, potentially impacting the S budget of large explosive eruptions. Here, we present the results of new experiments aimed at assessing the influence of the glass Ca content on SO₂ uptake in the temperature range of 600-800 °C. We exposed haplogranitic glasses to SO₂ for diverse time exposures (5-30 minutes). Rhyolitic composition was chosen due to the ubiquity of Si-rich magmas in large explosive eruptions (Cioni et al. 2000).

The experimental glasses were synthesized with an initial HPG8 composition (see Holtz et al. 1992), doped with 1 and 2 wt.% CaO. Furthermore, the role of Fe was tested by doping the glasses with 0, 0.1, 1, 1.5, 2 and 2.5 wt.% FeO and equilibrating them at 1500 °C. Leachates of post-treated glasses were analyzed by ion chromatography in order to determine SO₂-uptake and the nature of the sulfate-bearing minerals formed by solid-gas reactions. The bulk redox state of iron (Fe³⁺/Fe_total), was obtained by the K₂Cr₂O₇ potentiometric titration method. Our results show a strong correlation between the amount of Ca in the glasses and the formation of CaSO₄ surficial deposits (i.e. SO₂ uptake), i.e. the HPG8 + 2 wt.% CaO treated samples produced up to 40 % more CaSO₄ than the samples containing 1 wt.% CaO. Higher Fe content in the glass also enhanced formation of CaSO₄. In contrast, the absence of Fe oxide resulted in preferential formation of Na₂SO₄ and K₂SO₄, when compared to the Fe-bearing specimens. Our experiments confirm that high temperature SO₂ uptake by glass is strongly dependent on the Ca content and temperature, with the optimal reaction temperatures being ≥600 °C. Increasing the amount of FeO in the glasses seems to enhance SO₂ uptake, although this effect appears to be different for Ca than for Na or K, pointing out a more complex influence of redox dynamics on cation diffusion.

How to cite: Casas, A. S., Wadsworth, F. B., Ayris, P. M., Delmelle, P., Vasseur, J., Cimarelli, C., and Dingwell, D. B.: The role of calcium diffusion on high temperature SO2 uptake by volcanic glasses, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7102, https://doi.org/10.5194/egusphere-egu2020-7102, 2020.

Magmatic volatiles play a major role in controlling magma dynamics, such as ascent characteristics and eruption style. In order to fully understand their influence in magmatic systems, it is crucial to examine their behaviour within silicate melts. Although numerous studies have been conducted on volatile solubility, exsolution and degassing, some aspects of  magma degassing such as bubble formation, bubble growth and the affect on the distribution of fluid-mobile elements are poorly understood. For instance, magma degassing is likely to affect the abundance and dispersion of fluid-mobile elements, such as Li and B, in the magma. Thus, this study focuses on the diffusivity of Li and B in hydrated silicate melt as a proxy for degassing processes.

Lithium and boron are particularly suitable as geochemical tracers of degassing processes because they are light elements, present in natural volcanic systems in low concentrations, and have similar characteristics: both elements are fluid-mobile and each has two stable isotopes with different transport behaviours due to their atomic weights, which can lead to isotope fractionation. In order to successfully model their behaviour during magmatic ascent, their diffusivities in silicate melts have to be well constrained.

Diffusion data in hydrous settings are missing or underrepresented: very little studies have been conducted on boron diffusivity, the literature gives contradictory diffusion coefficients for lithium. In this study, we focus on elemental diffusion and isotopic fractionation of lithium and boron in hydrated silica-rich melts, in order to better understand B diffusivity and solve the discrepancies about Li data.

Sets of diffusion-couple experiments on synthetic water-bearing rhyolitic glasses have been performed, using an internally heated pressure vessel, at a constant pressure of 300 MPa and temperatures of 700°, 800° and 1000° C, with durations of 0 seconds, 30 minutes, 2 hours and 4 hours. Lithium and boron elemental concentrations have been measured by LA-ICP-MS, resulting in 600 μm long profiles, while isotopic ratios are being evaluated by SIMS analysis.

The zero-hour experiment indicates that lithium diffuses very rapidly, potentially already at temperatures below 700° C (during the heating process), while boron diffusion is generally slower, hence the necessity of higher temperatures and longer experimental run durations. Overall, our experimental results confirm previous literatue findings that Li diffuses faster in water-bearing melts, and give first constraints on boron diffusivity in hydrated silicate melts, whereas previous studies only considered anhydrous samples. The determination of diffusion coefficients of the two elements gives us a better understanding of the diffusion timescales. This information allows us to interpret additional decompression experiments, simulating a wide range of magma ascent rates, and to correlate the elemental and isotopic behaviour of lithium and boron with decompression-induced bubble formation processes.

How to cite: Spallanzani, R., Cichy, S. B., Oelze, M., Koga, K., Wilke, M., Fanara, S., and Sieber, M. J.: Li and B diffusivity in hydrated silicate melts: an experimental study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18180, https://doi.org/10.5194/egusphere-egu2020-18180, 2020.

Dominica island experienced the largest explosive eruptions (ignimbrites) of the Lesser Antilles arc. The recent revised chronostratigraphy of the Morne Trois Pitons – Micotrin eruptive activity evidenced a series of plinian eruptions that occurred between 18 ka and 9 ka BP. Here we focus on these recent eruptions in order to determine the magma storage conditions at depth and volatile degassing budget. Volatile concentrations (H₂O, CO₂) in melt inclusions indicate storage conditions of 200 MPa (~6-8 km deep) and 860-880°C in agreement with experimental constraints from phase-equilibrium data. The magmas were thus stored shallower than those involved during the ignimbritic eruptions (~16 km deep). Magma composition and halogen ratios suggest a common magma origin for all eruptions of Morne Trois Pitons Micotrin volcano in the last 60 kyrs. In addition, for the first time, a complete degassing budget including H₂O, CO₂, SO₂, F, Cl, and Br has been established for all these explosive eruptions. The estimation of their eruptive fluxes towards the atmosphere supports the potential important role of halogen elements in the modification of atmosphere chemistry. Br degassing budget was the same order of magnitude as S whereas F and Cl budgets were 1 and 2 orders of magnitude higher than these two species.

How to cite: d'Augustin, T., Balcone-Boissard, H., Boudon, G., Martel, C., Deloule, E., and Bürckel, P.: Dominica: transcrustal magmatic system and eruptive halogen budgets, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13591, https://doi.org/10.5194/egusphere-egu2020-13591, 2020.

The most recent activity of Piton des Neiges (La Réunion) is characterized by explosive behavior and relatively evolved magma compositions. These eruptions occurred roughly over the past 200 thousand years producing thick pyroclastic deposits, lava domes and block and ash flow deposits. We here present a detailed petrologic and geochronologic characterization of these deposits providing insights into the timing of explosive eruptions and pre-eruption magma storage conditions.

The early phase of explosive activity is characterized by up to 15 m-thick pyroclastic deposits found on the southeastern and western flanks of Piton des Neiges. These deposits have been regarded as individual discrete eruptions that occurred between 220 and 110 ka. Our detailed petrographical and geochemical study on juvenile fragments and the main mineral phases indicate that all deposits share similar geochemical fingerprints. High-precision single crystal ⁴⁰Ar/³⁹Ar dates on 70 alkali feldspars from 6 samples reveal significant dispersion but the youngest population of dated crystals from each sample yield overlapping weighted mean dates around 200 ka, supporting their geochemical correlation. The wide spread in ⁴⁰Ar/³⁹Ar dates of up to 88 kyrs prior to eruption, uncommon for alkali feldspar in volcanic rocks, argues for the presence of excess and/or inherited argon in those crystals. Together, our findings suggest that the early pyroclastic deposits are the product of a Plinian-type eruption that covered a large area of the island around 200 ka. The eruption was fed by a long-lived magma reservoir that produced differentiated magmas in response to lower recharge fluxes after the main active center migrated to the currently active Piton de la Fournaise. A wide range of mineral compositions and the strong disequilibrium between crystals and the trachytic groundmass is an indication of the pronounced heterogeneity of the magmatic reservoir following a deep recharge event that triggered the eruption.

The younger eruptive episode of Piton des Neiges occurred between 70 and 30 ka with dome-forming lavas of trachytic to rhyolitic composition that collapsed into pyroclastic density currents resulting in block and ash flow deposits found closer to the current summit. This eruptive style, infrequent in this geotectonic setting, has not yet been well recognized for Piton des Neiges. Pristine zircon crystals, found in a sample from a block and ash deposit, were dated with a total of 192 LA-ICP-MS spot analyses using the U-Th disequilibrium method, and constitute the first zircon geochronology study for this volcano. The results yield a well-defined isochron with a date of 44.80 ± 1.32 ka (2 S.E., MSWD = 1.2). Single crystal ⁴⁰Ar/³⁹Ar dates on alkali feldspars show a similar dispersion as for the older eruptive phase, but the youngest dates overlap with the zircon U-Th date, providing robust estimates of the eruption age.

This detailed characterization of the youngest eruptive episode of Piton des Neiges documents its explosive potential during the past 200 thousand years and has significant implications regarding the current view of Piton des Neiges as an extinct volcano.

How to cite: Castellanos Melendez, M. P., Ellis, B., Laurent, O., Wijbrans, J., Kuiper, K., Wotzlaw, J.-F., Di Muro, A., and Bachmann, O.: Characterizing the last explosive gasps of the Piton des Neiges (La Réunion Island) over the last 200 ka, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14840, https://doi.org/10.5194/egusphere-egu2020-14840, 2020.

Eruptive column models are crucial for managing volcanic crises, forecasting future events, and reconstructing past eruptions. Given their central role in volcanology and the large uncertainties weakening their predictions, the evaluation and improvement of these models is critical. Such evaluation is challenging as it requires independent estimates of the main model inputs (e.g. mass eruption rate) and outputs (e.g. column height). Despite recent efforts to extend datasets of independently estimated eruption source parameters (ESP) (e.g. Mastin 2014, Aubry et al. 2017), there is no standardized, maintained, and community-based ESP database devoted to the evaluation of eruptive column models.

Here we present a new ESP database designed to respond to the needs of the plume modelling community, and which will also be valuable to observatories, field volcanologists, and volcanic ash advisory centers. We compiled data for over 130 eruptive events with independent estimates of: i) the mass eruption rate; ii) the height reached by the column; and iii) atmospheric conditions during the eruption. In contrast with previous ESP datasets, we distinguish estimates of column height that relate to different phases (ash and SO2) and parts of the column (plume top or umbrella). We additionally provide the total grain size distribution, uncertainties in eruption parameters, and multiple sources for atmospheric profiles for events where these parameters are available. The database also includes a wealth of additional information which will enable modelers to distinguish between different eruptions when evaluating or calibrating models. This includes the type of eruption, the morphology of the plume (weak/transitional/strong), and the occurrence and mass entrained within pyroclastic density currents.

We will apply the new database to revisit empirical scaling relationships between the mass eruption rate and “plume height”. In particular, we will show how such relationships depend on the type of height (e.g. SO2 height vs. ash top height) and eruption (e.g. magmatic vs. phreatomagmatic) considered. We will also discuss the difficulties and limitations of compiling ESP estimates from the literature as well as characterizing fundamentally unsteady volcanic events by a single value for each ESP.

How to cite: Engwell, S., Aubry, T., Biass, S., Bonadonna, C., Bursik, M., Carazzo, G., Eychenne, J., Gouhier, M., Grainger, D., Jellinek, M., Jessop, D., Mastin, L., Pyle, D., Scollo, S., Taylor, I., Van Eaton, A., Wallace, K., and Woodhouse, M.: A new database of independently estimated eruption source parameters devoted to eruptive column model evaluation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5673, https://doi.org/10.5194/egusphere-egu2020-5673, 2020.

Morphological, textural and granulometric studies of volcanic ash particle provides important insights into the mechanisms of fragmentation, transport and deposition in the context of low-to-mid intensity activity, and particularly during those eruptions showing high-transients in the style of activity. A comprehensive study of volcanic ash from Vulcanian activity of variable intensity at Sakurajima volcano (Japan) is here presented together with a detailed analysis of ash aggregates collected and filmed during the same eruptive sequences. Bulk tephra deposits from different events (July-August 2013, October 2014 and November 2019) and high-speed video of falling ash aggregates were collected directly during the fallout. Tephra samples, resulting from the different phases of activity, were analyzed using an optical particle analyzer which allowed to characterized the grain size distribution and to quantify the shape of a large set of particles. A set of objective parameters were used to constrain the shape of ash grains. This helped to better characterize different phases of activity also in the light of the magma fragmentation process and to evaluate the role played by the fragmentation process in controlling the eruption dynamics. SEM analyses of representative ash grains allowed distinguishing four principal types of ash fragments basing on morphological, surface and groundmass features: Blocky Irregular (BI), Blocky Regular (BR), Vesicular (V). A comprehensive textural analysis of grains belonging to either the different classes and phases of activity was provided in order to better resolve the complex relationships between the processes occurring before and during magma fragmentation and secondary processes affecting ash characteristics, like the intra-crateric recycling of ash. This helped also to shed light on the different processes of ash production and link them with the resulting dynamics of activity in the context of unsteady eruptions. On the other hand, the analysis of the high-speed video depicting ash aggregates, and aggregates collected during the same eruptive periods revealed important information about the influence of ash aggregation in controlling the depositional dynamics of Vulcanian eruptions. Three main types of ash aggregates were recognized to occur into all the Sakurajima samples: Ash Clusters, Coated Particles, Cored Clusters. Using image analysis techniques of SEM images, collected aggregates were characterized in terms of dimension, grain size of the aggregating ash, and shape features of the aggregated ash, pointing out important differences between the different types. Analysis of high-resolution, High-speed Camera video recordings, allowed finally to collect an important set of measurements of terminal velocity, bulk density, and size of a large number of observed falling aggregates. The resulting data reveal the strong influence of aggregation processes in controlling ash deposition processes at Sakurajima, and also represent a valuable dataset useful for validation and calibration of numerical models.

How to cite: Gabellini, P., Bonadonna, C., Cioni, R., Pistolesi, M., Geshi, N., Rossi, E., and Bagheri, G.: Morpho-textural and dynamic analysis of ash particles and ash aggregates at Sakurajima volcano (Japan), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10166, https://doi.org/10.5194/egusphere-egu2020-10166, 2020.

Explosive volcanic eruptions emanate complex acoustic signals. They
are influenced by several parameters, most of most of which are highly
unconstrained in volcanic setting.

We investigate the acoustics of starting jets analogous to
volcanic jets at high Mach numbers and with different nozzle
geometries, in a controlled environment. For the first time in
volcanic analog studies, an anechoic chamber is used to eliminate
contamination of the signals by reflections from any wall or
obstacle.  The analysis concentrates on the identification of the
principal jet noise components including: compression waves, vortex
ring noise, turbulent jet mixing noise,  broadband shock noise and
screech. We employed a shock tube apparatus and signals were recorded
using a microphone array.  Employing wavelet analysis, we have
identified the noise sources in both time- and frequency-space.

We have identified the principal sound sources of the jet in
time-frequency space and have analyzed their behaviour with respect to
changes in pressure ratio $p/p_\infty$ ,non-dimensional mass supply
L/D and exit-to-throat area ratio.

We find that at higher pressure ratios the peak frequency of the
broadband shock noise is noticeably lower whereas the amplitude is
higher. The non-dimensional mass supply controls whether a jet forms
and its blowing duration and maximum velocity. The nozzle geometry has
a markable effect on delay of the shock-shear layer-vortex ring
interaction with respect to the compression wave.

Changes in parameters of the starting jet leave a clear and
interpretable trace in the observed sound pattern. This quantitative
parametrisation of these effects is essential for utilizing these
findings as well as field observations for the solution of the inverse
problem in the lab and in nature.

How to cite: Sesterhenn, J. L., Peña Fernández, J. J., Cigala, V., Küppers, U., and Dingwell, D.: Acoustic analysis of starting jets in an anechoic chamber, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15153, https://doi.org/10.5194/egusphere-egu2020-15153, 2020.