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18 results on '"Mader, H.M."'

3. The use of a shear-thinning polymer as a bubbly magma analogue for scaled laboratory experiments

Author

Jones, Thomas, Llewellin, E.W., Mader, H.M., Jones, Thomas, Llewellin, E.W., and Mader, H.M.

Abstract

Analogue materials are commonly used in volcanology to perform scaled laboratory experiments. Analogue experiments inform on fundamental fluid dynamic, structural and mechanical processes that are typically very difficult to observe and quantify directly in the natural volcanic system. Here we investigate the suitability of an aqueous solution of hydroxyethyl cellulose polymer (HEC) for use as a lava/magma analogue, with a particular focus on its rheological behaviour. We characterize a range of physical properties as functions of the concentration and temperature of the solution: density; specific heat capacity; thermal diffusivity; thermal conductivity; surface tension; as well as rheology. HEC has a non-Newtonian, shear-thinning rheology that depends on the concentration and temperature of the solution. We show that the rheology is well described by the Cross model, which was originally developed for polymer solutions, but has also been applied to bubbly magmas. Using this similarity, an approach for scaling analogue experiments that use shear-thinning polymers, like HEC, to bubbly magma is presented. A detailed workflow and a spreadsheet are provided to allow experimentalists to investigate the effects of non-Newtonian behaviour in their existing laboratory set-ups. This contribution will allow for the more complex, but often more realistic case of bubble-bearing magmas to be rigorously studied in experimental volcanology.

Published
2020

4. Experimental simulations of explosive degassing of magma

Author

Mader, H.M., Zhang, Y., Phillips, J.C., Sparks, R.S.J., Sturetevant, B., and Stolper, E.

Subjects
Volcanoes -- Research, Magma -- Research, Environmental issues, Science and technology, Zoology and wildlife conservation
Abstract

Simulations of volcanic explosions reveal that fragmentation is caused by expansion and acceleration of the bubbles in the magma. The bubbles are caused by the pyroclasts and gases in the magma flowing out from the volcano. The simulation utilizes a two model system which produces flow velocities and expansion rates of the bubbles that occur in the original magma. The expansion and acceleration depend on the liberation of CO2 from aqueous phase consisting of CO2, saturated water and concentrated K2CO3.

Published
1994

6. Laboratory simulations of sustained volcanic eruptions

Author

Mader, H.M., Brodsky, E.E., Howard, D., and Sturtevant, B.

Subjects
Volcanic activity prediction -- Research, Environmental issues, Science and technology, Zoology and wildlife conservation
Abstract

Researchers looking at sustained volcanic eruptions have been able to simulate volcanic conduit flows by rapidly decompressing large volumes of carbon dioxide-saturated water. This gives sustained explosions in a liquid where rapid exsolution of gas is taking place. It was established that the maximum average rate of propagation of the fragmentation region can be estimated if the conduit length is known. The start-up period identifies the time when the fragmentation region is propagating down the conduit.

Published
1997

7. The rheology of three-phase suspensions at low bubble capillary number

Author

Truby, J.M., Mueller, S.P., Llewellin, E.W., and Mader, H.M.

Subjects
Condensed Matter::Soft Condensed Matter, Physics::Fluid Dynamics, bubble suspension, particle suspension, three phase, rheology, Research Articles, analogue experiments
Abstract

We develop a model for the rheology of a three-phase suspension of bubbles and particles in a Newtonian liquid undergoing steady flow. We adopt an 'effective-medium' approach in which the bubbly liquid is treated as a continuous medium which suspends the particles. The resulting three-phase model combines separate two-phase models for bubble suspension rheology and particle suspension rheology, which are taken from the literature. The model is validated against new experimental data for three-phase suspensions of bubbles and spherical particles, collected in the low bubble capillary number regime. Good agreement is found across the experimental range of particle volume fraction ([Formula: see text]) and bubble volume fraction ([Formula: see text]). Consistent with model predictions, experimental results demonstrate that adding bubbles to a dilute particle suspension at low capillarity increases its viscosity, while adding bubbles to a concentrated particle suspension decreases its viscosity. The model accounts for particle anisometry and is easily extended to account for variable capillarity, but has not been experimentally validated for these cases.

Published
2015

12. Evolution of chemical peak shapes in the Dome C, Antarctica, ice core

Author

Barnes, P.R.F., Wolff, E.W., Mader, H.M., Udisti, R., Castellano, E., Röthlisberger, R., Barnes, P.R.F., Wolff, E.W., Mader, H.M., Udisti, R., Castellano, E., and Röthlisberger, R.

Abstract

[1] Interpretation of the chemical layers measured in ice cores requires knowledge of processes occurring after their deposition on the ice sheet. We present evidence for the diffusion of soluble ions in the top 350 m of the Dome C ice core, Antarctica, that helps in explaining the unexpectedly broad volcanic peaks observed at depth. A windowed-differencing operation applied to chemical time series indicates a damping of the signals over the past 11,000 years, independent of minor climatic variation, for sulfate and chloride, but not sodium. This implies a diffusive process is transporting both sulfate and chloride ions while the sodium ions remain fixed. We estimate the effective diffusivity in the core to be 4.7 x 10(-8) m(2) yr(-1) for sulfate and 2.0 x 10(-7) m(2) yr(-1) for chloride. These values are not high enough to significantly disrupt chemical interpretation in this section of core, but could be significant for older ice. The temperature of this section of ice (-53degreesC) implies that the predominantly acidic sulfate (and possibly chloride ions) will exist in the liquid phase while the sodium may be solid. We propose and develop two new mechanisms that could explain the observed solute movement. One involves the diffusion of solute through a connected vein network driven by liquid concentration imbalances instigated by the process of grain growth. The other considers a system of discontinuous veins where grain growth increases connectivity between isolated vein clusters allowing the spread of solute. In both mechanisms, the effective diffusivity is governed indirectly by grain growth rate; this may be a significant factor controlling effective diffusion in other cores.

Published
2003

17. The rheology of two-phase magmas: A review and analysis.

Author

Mader, H.M., Llewellin, E.W., and Mueller, S.P.

Subjects
*RHEOLOGY, *MAGMAS, *CRYSTALS, *IGNEOUS rocks, *PROPERTIES of matter, *EARTH sciences
Abstract

Abstract: We consider the current state of our understanding of the rheology of two-phase magmas, that is suspensions of either bubbles or crystals in a viscous silicate melt. The discussion is restricted to strain-rates at which the suspending melt can be considered Newtonian. We start by considering the range of textures found in magmas and the bubble deformation and particle motions caused by shearing. We then review proposed models for suspensions, focussing on those functions of the form η r = f(ϕ) or that have been most widely used to describe magmatic systems (η r is the relative apparent viscosity of the suspension, ϕ is the volume fraction of the suspended phase, τ is the driving stress, and is the strain-rate). Both theoretical and empirical methods are presented and then compared against the available analogue (i.e. non-magmatic) and magmatic data. The paper contains new data and significant re-analysis of previously published data. We present a new semi-empirical constitutive model for bubble-bearing magmas that is valid for steady and unsteady flow and large strains and strain-rates. This equation utilises a new parameter, the capillarity Cx, that encapsulates the combined effect of shearing and unsteadiness on bubble suspensions. We also present a new scheme for dealing with polydispersivity of bubble suspensions. New data on the rheology of particle suspensions undergoing forced-oscillations are presented. These data show that the Cox–Merz rule only holds for dilute particle suspensions ϕ ≲0.25. A re-analysis of all available experimental data that relate rheology to particle aspect ratio provides distinct curves of maximum packing as a function of aspect ratio for smooth and rough particles with magmatic data lying on the curve appropriate for rough particles. We analyse several rheological datasets of crystal-bearing basaltic magmas and find that they are in good agreement with the constitutive equations derived from analogue data. By contrast, the same equations do not agree well with data for high-viscosity, haplogranitic melts. This may be an effect of fracturing or viscous dissipation within these samples. The paper concludes with a practical ‘rheological recipes’ section giving a step-by-step method for calculating a constitutive equation for a two-phase magmatic suspension and assessing its likely accuracy. [Copyright &y& Elsevier]

Published
2013
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18. From magma ascent to ash generation: investigating volcanic conduit processes by integrating experiments, numerical modeling, and observations

Author

Fabio Arzilli, Luca Caricchi, Chiara Paola Montagna, Lucia Gurioli, Nicole Métrich, Simone Colucci, Heidi Marita Mader, Mike Burton, Antonio Costa, Mattia de' Michieli Vitturi, Jacopo Taddeucci, Yan Lavallée, Corrado Cimarelli, Augusto Neri, Daniele Giordano, Edward W. Llewellin, Timothy H. Druitt, Tomaso Esposti Ongaro, Amanda Clarke, Freysteinn Sigmundsson, B. B. Carr, Gilberto Saccorotti, Margherita Polacci, Samantha Engwell, Ulrich Kueppers, Eleonora Rivalta, Matteo Cerminara, Anthony Lamur, Baptiste Haddadi, Wim Degruyter, Laura Spina, Jackie E. Kendrick, University of Manchester [Manchester], Istituto Nazionale di Geofisica e Vulcanologia – Sezione di Pisa (INGV), Istituto Nazionale di Geofisica e Vulcanologia, Université de Genève = University of Geneva (UNIGE), Arizona State University [Tempe] (ASU), Ludwig Maximilian University [Munich] (LMU), Istituto Nazionale di Geofisica e Vulcanologia - Sezione di Bologna (INGV), Cardiff University, Laboratoire Magmas et Volcans (LMV), Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Institut de Recherche pour le Développement et la société-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS), British Geological Survey [Edinburgh], British Geological Survey (BGS), Università degli studi di Torino = University of Turin (UNITO), University of Liverpool, Durham University, University of Bristol [Bristol], Institut de Physique du Globe de Paris (IPGP), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS), GeoForschungsZentrum - Helmholtz-Zentrum Potsdam (GFZ), University of Iceland [Reykjavik], Polacci M., de' Michieli Vitturi M., Arzilli F., Burton M.R., Caricchi L., Carr B., Cerminara M., Cimarelli C., Clarke A.B., Colucci S., Costa A., Degruyter W., Druitt T., Engwell S., Ongaro T.E., Giordano D., Gurioli L., Haddadi B., Kendrick J.E., Kueppers U., Lamur A., Lavallee Y., Llewellin E., Mader H.M., Metrich N., Montagna C., Neri A., Rivalta E., Saccorotti G., Sigmundsson F., Spina L., Taddeucci J., Université de Genève (UNIGE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet [Saint-Étienne] (UJM)-Institut de Recherche pour le Développement et la société-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Università degli studi di Torino (UNITO), Centre National de la Recherche Scientifique (CNRS)-Université de La Réunion (UR)-Université Paris Diderot - Paris 7 (UPD7)-IPG PARIS-Institut national des sciences de l'Univers (INSU - CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet [Saint-Étienne] (UJM)-Institut de Recherche pour le Développement et la société-Université Clermont Auvergne (UCA)-Centre National de la Recherche Scientifique (CNRS)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), and Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)

Subjects
0301 basic medicine, Volcanic hazards, theoretical and observational volcanology, 010504 meteorology & atmospheric sciences, Volcanic processes, Earth science, Volcanic conduit, 01 natural sciences, Magma (computer algebra system), Modelling, 03 medical and health sciences, Experimental, Lead (geology), Volcanic activity, Multidisciplinary approach, ddc:550, [SDU.STU.VO]Sciences of the Universe [physics]/Earth Sciences/Volcanology, Disequilibrium, Uncertainty S0666, Unsteadiness, Risk management, 0105 earth and related environmental sciences, computer.programming_language, disequilibrium, geography, geography.geographical_feature_category, Breakout, business.industry, Unsteadine, Uncertainty, Magma ascent, Volcanology, 030104 developmental biology, Geophysics, Volcano, Field practice, 13. Climate action, Experiments, business, computer, Geology
Abstract

Processes occurring in volcanic conduits, the pathways through which magma travels from its storage region to the surface, have a fundamental control on the nature of eruptions and associated phenomena. It has been well established that magma flows, crystallizes, degasses, and fragments in conduits, that fluids migrate in and out of conduits, and that seismic and acoustic waves are generated and travel within conduits. A better un- derstanding of volcanic conduits and related processes is of paramount importance for improving eruption forecasting, volcanic hazard assess- ment and risk mitigation. However, despite escalating advances in the characterization of individual conduit processes, our understanding of their mutual interactions and the consequent control on volcanic activity is still limited. With the purpose of addressing this topic, a multidisci- plinary workshop led by a group of international scientists was hosted from 25 to 27 October 2014 by the Pisa branch of the Istituto Nazionale di Geofisica e Vulcanologia under the sponsorship of the MeMoVolc Re- search Networking Programme of the European Science Foundation. The workshop brought together the experimental, theoretical, and observa- tional communities devoted to volcanological research. After 3 days of oral and poster presentations, breakout sessions, and plenary discussions, the participants identified three main outstanding issues common to ex- perimental, analytical, numerical, and observational volcanology: unsteadiness (or transience), disequilibrium, and uncertainty. A key out- come of the workshop was to identify the specific knowledge areas in which exchange of information among the sub-disciplines would lead to efficient progress in addressing these three main outstanding issues. It was clear that multidisciplinary collaboration of this sort is essential for progressing the state of the art in understanding of conduit magma dynamics and eruption behavior. This holistic approach has the ultimate aim to deliver fundamental improvements in understanding the underly- ing processes generating and controlling volcanic activity.

Published
2017
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