Anja Allabar

University of Tübingen

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Marcus Nowak

University of Tübingen

Katherine J. Dobson

Durham University

Fabian B. Wadsworth

Ludwig-Maximilians-Universität München

Donald B. Dingwell

Ludwig-Maximilians-Universität München

Federica Marone

Paul Scherrer Institute

Jérémie Vasseur

Ludwig-Maximilians-Universität München

Jason P. Coumans

Durham University

Edward W. Llewellin

Durham University

James E. Gardner

The University of Texas at Austin

Christian Bauer

Technical University of Applied Sciences Würzburg-Schweinfurt

Cooperative Institutions

Ludwig-Maximilians-Universität München

Durham University

Universidade de São Paulo

LMU Klinikum

University of Tübingen

University of Oxford

University of Liverpool

Centre National de la Recherche Scientifique

University of Bristol

University of Cambridge

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Growth and Resorption of Bubbles in Magma

Goldschmidt Abstracts (2020)

Edward W. Llewellin Jason P. Coumans Fabian B. Wadsworth Madeleine C. S. Humphreys Katherine J. Dobson

The rate and timing of bubble growth in magma is an important control on eruption style, determining whether or not magma fragments to produce an explosive eruption. Bubbles nucleate, grow, shrink, and de-nucleate in magma in response to changes in pressure and temperature, and these changes may be recorded in the vesicle textures, and in the spatial distribution and speciation of water ‘frozen into’ the glass in eruption products. We have developed a numerical model for growth and resorption of bubbles in magma, and validated it against experiments across a wide range of conditions. The model allows for arbitrary temperature and pressure pathways, and accounts for the impact of spatial variations in water content on diffusivity and viscosity. Textures in natural, vesicular volcanic rocks are often used to interpret eruptive processes. Similarly, high-pressure, high-temperature experiments are used to probe bubble growth processes, via textural and chemical analysis of the experimental products. However, in both cases, the analysed samples have cooled from magmatic temperatures before analysis, providing a window for thermally-driven bubble shrinkage and resorption to modify the sample. Consequently, interpretations of syn-eruptive and syn-experimental processes must account for changes during cooling. We present results from in situ experiments under synchrotron-source tomography, which demonstrate the thermally driven growth and resorption of bubbles in magma at one atmosphere. The model is applied to 4D textural data, and used to investigate the role of bubble-bubble interactions in modifying growth and resorption behaviour. We also apply the model to re-analyse the results of high-temperature, highpressure experiments, and demonstrate the importance of accounting for thermal resorption during cooling.

10.46427/gold2020.1629

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Comment on the paper by Buono et al. “Dynamics of degassing in evolved alkaline magmas: Petrological, experimental and theoretical insights” (Earth Science Reviews, 211 (2020), 103402)

Earth-Science Reviews (2021)

Anja Allabar Marcus Nowak

Escarpment

Island arc

Continental Margin

Back-arc basin

Passive margin

Volcanic arc

10.1016/j.earscirev.2021.103655

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Quantifying Microstructural Evolution in Moving Magma

Frontiers in Earth Science (2020)

Katherine J. Dobson Anja Allabar Eloïse Bretagne Jason P. Coumans Michael Cassidy

Many of the grand challenges in volcanic and magmatic research are focused on understanding the dynamics of highly heterogeneous systems, and the critical conditions which enable magmas to move, or eruptions to initiate. From the formation and development of magma reservoirs, through propagation and arrest of magma, to the conditions in the conduit, gas escape, eruption dynamics and beyond into the environmental impacts of that eruption: we are trying to define how processes occur, their rates and timings, their causes and consequences. However, we are usually unable to observe the processes directly. Here we give a short synopsis of the new capabilities and highlight the potential insights that in situ observation can provide. We present the XRheo and Pele furnace experimental apparatus and analytical toolkit for the in situ X-ray tomography based quantification of magmatic microstructural evolution during rheological testing. We present the first 3D data showing the evolving textural heterogeneity within a shearing magma, highlighting the dynamic changes to microstructure that occur from the initiation of shear, and the variability of the microstructural response to that shear as deformation progresses. The detailed, in-situ, characterization of sample textures presented here therefore represents the opening of a new field for the accurate parameterization of dynamic microstructural control on rheological behavior.

Shearing (physics)

Characterization

10.3389/feart.2020.00287

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Citations (13)

Correction to: “Vesicle shrinkage in hydrous phonolitic melt during cooling”

Contributions to Mineralogy and Petrology (2020)

Anja Allabar Katherine J. Dobson Christian Bauer Marcus Nowak

Shrinkage

10.1007/s00410-020-01683-3

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Message in a bottle: Spontaneous phase separation of hydrous Vesuvius melt even at low decompression rates

Earth and Planetary Science Letters (2018)

Anja Allabar Marcus Nowak

Violent explosive volcanic eruptions are destructive and threaten millions of people and infrastructure. Ejected ash, pumice and gases are end-products of volcanic factories sourced deep within magma chambers and conduits. The different production stages are not directly observable. However, experimental simulation reveals different stages of dynamic volcanic processes. The starting point of explosive volcanic eruptions is determined by the phase separation of an H2O fluid from a supersaturated hydrous silicate melt. The number of formed H2O fluid vesicles per unit volume of silicate melt (VND) is a basic property that controls the efficiency of fluid-melt separation, ascent velocity and finally explosive volcanism. We performed decompression experiments at superliquidus temperatures to simulate phase separation of a single phase hydrous silicate melt during ascent with AD79 Vesuvius white pumice composition using decompression rates of 0.024–1.7 MPa⋅s−1. The white pumice buried Herculaneum and Pompeii and is representative of other catastrophic phonolitic and trachytic explosive eruptions like the violent 39 ka Campi Flegrei and the 1815 AD Tambora eruption. Here we report a high log⁡VND of 5.2 (in mm−3) that is independent from decompression rate within the investigated range. Even at a decompression rate of 0.024 MPa⋅s−1 the formation of a high VND inevitably causes rapid degassing due to short H2O diffusion distances from the melt into fluid vesicles. A decompression rate meter based on nucleation theory, which is commonly used to estimate magma ascent velocity during volcanic eruptions using VND of volcanic ejecta, cannot be adapted to explain our experimentally determined decompression rate independent VND. Alternatively, decompression induced H2O–silicate melt phase separation may be described by diffusion controlled spinodal decomposition where maximum supersaturation is reached. This process occurs spontaneously and free of activation energy if hydrous melt is driven into thermodynamic instability where the second derivative of free energy of mixing to the H2O content is ≤0. However, the decompression rate independent VND has profound consequences for the dynamics of natural polyphase hydrous magma phase separation. Even at low ascent rates spontaneous hydrous melt phase separation facilitates rapid density decrease accompanied by sudden increase of magma buoyancy triggering explosive eruptions.

Pumice

Trachyte

10.1016/j.epsl.2018.08.047

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Viscosity of Palmas-type magmas of the Paraná Magmatic Province (Rio Grande do Sul State, Brazil): Implications for high-temperature silicic volcanism

Chemical Geology (2020)

D. Giordano Alessandro Vona Diego González‐García Anja Allabar S. Kolzenburg

Silicic

Anhydrous

Depolymerization

10.1016/j.chemgeo.2020.119981

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Melt degassing triggered by magma injection?

Patricia Petri Anja Allabar Marcus Nowak

Explosive eruptions of silicic magmas depend mainly on the amount and the degassing behavior of soluble volatile components like H2O and CO2. The injection of a hot mafic magma into a cooler volatile-rich rhyolitic magma chamber might initiate mingling and mixing processes at the interface of the two melt reservoirs (Paredes-Marino et al. 2017). An accompanying increase in temperature and a buoyant ascent of the H2O-saturated rhyolitic melt may cause a sufficiently high decrease in solubility at pressures < 300 MPa (e.g. Holtz et al. 1995) to trigger vesicle formation. Furthermore, the interface between different melt compositions might act as a site for enhanced vesicle formation. To test this hypothesis, bimodal decompression experiments were conducted. Basaltic and rhyolitic compositions similar to the Askja eruption 1875 in Iceland (Sparks and Sigurdsson 1977) were used for this purpose. For the preparation of the experiments, rhyolitic and basaltic glass cylinders were molten and hydrated separately in an internally heated argon pressure vessel with H2O excess at 200&#160;MPa and 1523 K for 96&#8211;168&#160;h and then isobarically quenched with 16&#160;K&#8729;s&#8209;1. The hydrated glass samples were cut perpendicular to the cylinder axis. The cylinder faces were polished to enable a perfect contact of the rhyolite cylinder with the basalt cylinder. An additional decompression experiment with two contacted hydrated rhyolite cylinders was conducted as a reference to test the experimental setup.Each pair of cylinders was heated isobarically with 25 K&#183;s-1 to 1348 K at 210 MPa and equilibrated for 10&#160;min. To simulate the magma ascent, three bimodal samples and the reference sample were decompressed with rates of 0.17&#160;MPa&#8729;s-1 or 1.7 MPa&#8729;s-1 to the final pressure of 100 MPa and then quenched with 44&#160;K&#8729;s-1. H2O vesicle number and spatial distribution as well as the H2O contents in the decompressed samples were analysed by microscope, quantitative BSE image analysis, and FTIR-spectroscopy, respectively.All decompression experiments resulted in vesiculated samples. In the rhyolite reference experiment, the H2O vesicles are homogeneously distributed within the whole sample. The former interface of the cylinders is no longer visible. This confirms that the former contact plane of the cylinders does not influence the degassing behaviour during decompression.Optical examination and electron microprobe analysis of oxide diffusion profiles of the decompressed bimodal samples expose the development of a hybrid melt zone between the rhyolite and the partially crystallized basalt, documenting mixing processes during the decompression experiments (Petri 2020). The hybrid zone in the rhyolitic compositional dominated region is decorated with an enhanced number of H2O vesicles compared to the rhyolitic and basaltic glass volumes. This suggests that the injection of a basaltic melt into a rhyolitic melt reservoir may lead to significantly enhanced homogeneous H2O vesicle formation in the hybrid zone and, therefore, enhanced degassing with the concomitant triggering of explosive eruptions.&#160;Holtz F. et al. (1995) American Mineralogist 80: 84-108.Paredes-Marino J. et al. (2017) Scientific Reports 7: 16897.Petri P. (2020) Master thesis University of T&#252;bingen.Sparks S.R.J. and Sigurdsson H. (1977) Nature 267: 315-318.

Silicic

10.5194/egusphere-egu21-6511

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High spatial resolution analysis of H2O in silicate glass using attenuated total reflection FTIR spectroscopy coupled with a focal plane array detector

Chemical Geology (2020)

Anja Allabar Marcus Nowak

High resolution spectroscopic techniques that are used to determine volatile concentration in geological glasses are on the forefront for determining small scale degassing or hydration processes. Several spectroscopic methods are used for this purpose but they mostly require complicated sample preparation. Here, these methods are extended by the use of attenuated total reflectance (ATR) FTIR spectroscopy coupled with a focal plane array detector (FPA). ATR-FTIR spectroscopy requires only singly polished samples. The coupling to an FPA detector, which is novel for the analysis of volatile bearing glasses, enables spatial resolution on a micrometer scale. An ATR-FPA calibration to quantify H2O concentration in peralkaline rhyolitic glass is presented, which is comparable to conventional ATR calibrations using a single element detector. The results confirm that calibrations for different glass compositions are comparable after correction for glass density as suggested by a previous study. A method is developed to compare calibrations obtained with ATR objectives that have different angles of incidence. Despite the larger errors that come with the use of an FPA detector, the method allows the detection of H2O concentration gradients on a micrometer scale. The ATR-FPA calibration was applied to experimentally vesiculated melts that were quenched to glasses. It was possible to resolve only several μm-sized H2O resorption halos around vesicles that formed during isobaric cooling. Besides vesiculated glasses, the new method may enable the analysis of small melt inclusions and partially crystallized glasses and may allow the spatially resolved analysis of CO2 dissolved in silicate glasses.

Attenuated total reflection

10.1016/j.chemgeo.2020.119833

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An empirical H2O solubility model for peralkaline rhyolitic melts

Contributions to Mineralogy and Petrology (2022)

Anja Allabar Patricia L. Petri Dennis Eul Marcus Nowak

Peralkaline rock

Molar solubility

10.1007/s00410-022-01915-8

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Citations (3)

In situ observation of the percolation threshold in multiphase magma analogues

Bulletin of Volcanology (2020)

Mathieu Colombier Fabian B. Wadsworth Bettina Scheu Jérémie Vasseur Katherine J. Dobson

Magmas vesiculate during ascent, producing complex interconnected pore networks, which can act as outgassing pathways and then deflate or compact to volcanic plugs. Similarly, in-conduit fragmentation events during dome-forming eruptions create open systems transiently, before welding causes pore sealing. The percolation threshold is the first-order transition between closed- and open-system degassing dynamics. Here, we use time-resolved, synchrotron-source X-ray tomography to image synthetic magmas that go through cycles of opening and closing, to constrain the percolation threshold ΦC at a range of melt crystallinity, viscosity and overpressure pertinent to shallow magma ascent. During vesiculation, we observed different percolative regimes for the same initial bulk crystallinity depending on melt viscosity and gas overpressure. At high viscosity (> 106 Pa s) and high overpressure (~ 1-4 MPa), we found that a brittle-viscous regime dominates in which brittle rupture allows system-spanning coalescence at a low percolation threshold (ΦC ~0.17) via the formation of fracture-like bubble chains. Percolation was followed by outgassing and bubble collapse causing densification and isolation of the bubble network, resulting in a hysteresis in the evolution of connectivity with porosity. At low melt viscosity and overpressure, we observed a viscous regime with much higher percolation threshold (ΦC > 0.37) due to spherical bubble growth and lower degree of crystal connection. Finally, our results also show that sintering of crystal-free and crystal-bearing magma analogues is characterised by low percolation thresholds (ΦC = 0.04 - 0.10). We conclude that the presence of crystals lowers the percolation threshold during vesiculation and may promote outgassing in shallow, crystal-rich magma at initial stages of Vulcanian and Strombolian eruptions.

Overpressure

Outgassing

10.1007/s00445-020-1370-1

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Citations (30)