Understanding which parameters control shallow ascent of silicic effusive magma

Thomas, Mark; Neuberg, Jürgen

doi:10.1002/2014gc005529

Cited by 11 publications

(12 citation statements)

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“…In recent years, several well‐monitored lava dome volcanoes have provided a wealth of geophysical data that are rapidly changing our understanding of eruption mechanisms. The integration of seismic and tilt signals has proven helpful to track pressure evolution during dome eruptions (Chouet & Matoza, ; Johnson et al, ; Thomas & Neuberg, ; Voight et al, ). Seismicity provides evidence for magma fracturing (Bean et al, ; Lamb et al, ; Neuberg et al, ) and gas flux (Chouet, ; Matoza et al, ) during transitions to explosive activity, while proximal monitoring of tilt signals at dome volcanoes has identified shallow (<500 m) inflation for several minutes prior to vulcanian explosions (Johnson et al, ; Lyons et al, ; Nishimura et al, ).…”

Section: Introductionmentioning

confidence: 99%

Brittle‐Ductile Deformation and Tensile Rupture of Dome Lava During Inflation at Santiaguito, Guatemala

et al. 2019

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Gas-and-ash explosions at the Santiaguito dome complex, Guatemala, commonly occur through arcuate fractures, following a 5-to 6-min period of inflation observed in long-period seismic signals. Observation of active faults across the dome suggests a strong shear component, but as fault propagation generally proceeds through the coalescence of tensile fractures, we surmise that explosive eruptions require tensile rupture. Here, we assess the effects of temperature and strain rate on fracture propagation and the tensile strength of Santiaguito dome lavas. Indirect tensile tests were conducted on samples with a porosity range of 3-30% and over diametral displacement rates of 0.04, 0.004, and 0.0004 mm/ s. At room temperature, the tensile strength of dome rock is rate independent (within the range tested) and inversely proportional to the porosity of the material. At eruptive temperatures we observe an increasingly ductile response at either higher temperature or lower displacement rate, where ductile deformation is manifest by a reduction in loading rate during constant deformation rate tests, resulting in slow tearing, viscous flow, and pervasive damage. We propose a method to conduct indirect tensile tests under volcanic conditions using a modification of the Brazilian disc testing protocol and use brittleness indices to classify deformation modes across the brittle-ductile transition. We show that a degree of ductile damage is inevitable in the lava core during explosions at the Santiaguito dome complex and discuss how strain leading to rupture controls fracture geometry, which would impact gas pressure release or buildup and regulate explosive activity.Plain Language Summary Using instruments we installed at Santiaguito, an active lava dome complex in Guatemala, we detected repeating cycles of inflation and deflation. The inflation took less time leading up to explosions compared to weak gas puffing, which led us to suspect that lava breaking and flowing might be responsible. To investigate this, we made laboratory tests where we put lava samples under tension, which is the most common way they break. We ran tests where we squeezed lavas at faster and slower rates in a press, and we also heated the lavas to their eruption temperatures-about 800°C-for some tests. Since the lavas contain volcanic glass, in some high temperature tests the glass partially flowed. In other tests the lavas were completely brittle, which means they stored up stress and then broke without flowing. The lava's behavior depends on the temperature and how fast they are squeezed. Finally, we considered how fast dome lavas at Santiaguito would have to be deformed to either break or stay intact during inflation of the dome. This study gives us a better idea of how dome lavas deform and how that affects hazardous activity during eruptions.

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Section: Introductionmentioning

confidence: 99%

Brittle‐Ductile Deformation and Tensile Rupture of Dome Lava During Inflation at Santiaguito, Guatemala

et al. 2019

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“…The 2D axisymmetric flow modeling in this project builds upon the work of Collier and Neuberg (2006) and Thomas and Neuberg (2014), and is performed using the Laminar Flow Module in the finite element software COMSOL Multiphysics 5.3. 1D models have been used successfully to discern volcanic phenomena, such as lava dome extrusion (Melnik and Sparks, 1999) and plug formation (Diller et al, 2006).…”

Section: Flow Model Set-upmentioning

confidence: 99%

“…The gas volume fraction remaining in the magma is a key factor in determining whether magma fragmentation occurs, and therefore whether a subsequent eruption is effusive or explosive (Dingwell, 1996). Additionally, the remaining gas content influences both the viscosity (Llewellin and Manga, 2005) and density (Spera, 2000) of the bulk magma, and therefore provides a top-down control on the magma ascent rate (Thomas and Neuberg, 2014). Therefore, it is important to be able to quantify how much gas is lost from the system.…”

Section: Bubbly Magmamentioning

confidence: 99%

“…This allows us to quantify how both pressure and shear stress vary within a volcanic conduit. Thomas and Neuberg (2012) showed that variations in conduit geometry can significantly increase the shear stress locally to potentially induce seismicity through brittle failure of magma, and in further work (Thomas and Neuberg, 2014) identified volatile content and the driving pressure gradient as key parameters in modulating the ascent dynamics and therefore shear stress and pressure. Okumura and Kozono (2017) demonstrated that the transition from viscous flow to frictioncontrolled slip occurs at a greater depth if the crystal content is higher, as strain localizes in the melt phase where crystals are assumed rigid.…”

Section: Introductionmentioning

confidence: 99%

“…Moving on from these studies, we investigate whether observed deformation can be explained using realistic depthdependent pressure and shear stress profiles, obtained through flow modeling. Here, we build upon the 3 phase, 2D axisymmetric flow models of Collier and Neuberg (2006) and Thomas and Neuberg (2014) to simulate more realistic conditions during ascent of magma through a cylindrical conduit. From this, we obtain depth-dependent pressure and shear stress profiles at the conduit-edifice boundary, which we use to drive our deformation modeling.…”

Section: Introductionmentioning

confidence: 99%

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Combining Magma Flow and Deformation Modeling to Explain Observed Changes in Tilt

et al. 2019

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The understanding of magma ascent dynamics is essential in forecasting the scale, style and timing of volcanic eruptions. The monitoring of near-field deformation is widely used to gain insight into these dynamics, and has been linked to stress changes in the upper conduit. The ascent of magma through the conduit exerts shear stress on the conduit wall, pulling up the surrounding edifice, whilst overpressure in the upper conduit pushes the surrounding edifice outwards. How much shear stress and pressure is produced during magma ascent, and the relative contribution of each to the deformation, has until now only been explored conceptually. By combining flow and deformation modeling using COMSOL Multiphysics, we for the first time present a quantitative model that links magma ascent to deformation. We quantify how both shear stress and pressure vary spatially within a cylindrical conduit, and show that shear stress generally dominates observed changes in tilt close to the conduit. However, the relative contribution of pressure is not insignificant, and both pressure and shear stress must be considered when interpreting deformation data. We demonstrate that significant changes in tilt can be driven by changes in the driving pressure gradient or volatile content of the magma. The relative contribution of shear stress and pressure to the tilt varies considerably depending on these parameters. Our work provides insight into the range of elastic moduli that should be considered when modeling edifice-scale rock masses, and we show that even where the edifice is modeled as weak, shear stress generally dominates the near field deformation over pressurization of the conduit. While our model addresses cyclic tilt changes observed during activity at Tungurahua volcano, Ecuador, between 2013 and 2014, it is also applicable to silicic volcanoes in general.

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Crystals, Bubbles and Melt: Critical Conduit Processes Revealed by Numerical Models

Thomas

Neuberg

Collinson

2018

Advances in Volcanology

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Understanding how magma moves within a conduit is an important question that is still poorly understood. In particular, estimation of the magma ascent rate is key for interpreting monitoring signals and therefore, predicting volcanic activity. This relies on understanding how strongly different magmatic processes occurring within the conduit control the ascent rate. These processes are controlled by changes in magmatic parameters such as the water content or temperature and understanding/ linking changes of such parameters to monitoring data is an essential step in the use of these data as a predictive tool. The results presented here are from a suite of conduit flow models based on Soufrière Hills Volcano, Montserrat, that assesses the influence of individual model parameters. By systematically changing these parameters, the results indicate that changes in conduit diameter and excess pressure in the magma chamber are amongst the dominant controlling variables. However, the single most important parameter controlling variations in the magma ascent rate is the volatile content. Therefore, understanding the processes controlling the volatile content within the conduit system and the outgassing of these volatiles is crucial to understanding and predicting potential unrest or eruption scenarios.

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Understanding which parameters control shallow ascent of silicic effusive magma

Cited by 11 publications

References 68 publications

Brittle‐Ductile Deformation and Tensile Rupture of Dome Lava During Inflation at Santiaguito, Guatemala

Brittle‐Ductile Deformation and Tensile Rupture of Dome Lava During Inflation at Santiaguito, Guatemala

Combining Magma Flow and Deformation Modeling to Explain Observed Changes in Tilt

Crystals, Bubbles and Melt: Critical Conduit Processes Revealed by Numerical Models

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