Experimental constraints on volcanic ash generation and clast morphometrics in pyroclastic density currents and granular flows

Hornby, Adrian; Kueppers, Ulrich; Maurer, Benedikt; Poetsch, Carina; Dingwell, Donald B.

doi:10.30909/vol.03.02.263283

Cited by 16 publications

(10 citation statements)

References 78 publications

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“…Pumice clasts from the CE 1660 pumice flow deposit are white-beige in colour and have smooth, subrounded to rounded shapes due to abrasion and rounding of clasts during transport (e.g. Manga et al 2011;Buckland et al 2018;Hornby et al 2020). Pumice clasts from the same eruption but sampled at the fallout deposit around El Refugio are subangular and have an orange-beige colour, likely as a result of alteration.…”

Section: Macroscopic Descriptionmentioning

confidence: 99%

Conduit processes in crystal-rich dacitic magma and implications for eruptive cycles at Guagua Pichincha volcano, Ecuador

et al. 2022

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Stratovolcanoes are commonly characterised by cyclic eruptive activity marked by transitions between dome-forming, Vulcanian, Subplinian and Plinian eruptions. Guagua Pichincha volcano (Ecuador) has been a location of such cyclicity for the past ~ 2000 years, with Plinian eruptions in the first and tenth centuries AD (Anno Domini/after Christ), and CE (Common Era) 1660, which were separated by dome-forming to Subplinian eruptions, such as the recent 1999–2001 eruption. These cycles are therefore a prominent example of effusive-explosive transitions at varying timescales. Here, we investigate the reasons for such shifts in activity by focusing on degassing and outgassing processes within the conduit. We have coupled a petrophysical and textural analysis of dacites from the CE 1660 Plinian eruption and the 1999–2001 dome-forming/Vulcanian eruption, with different percolation models in order to better understand the role of degassing on eruptive style. We demonstrate that the transition from dome-forming to Plinian activity is correlated with differences in phenocryst content and consequently in bulk viscosity. A lower initial phenocryst content and viscosity is inferred for the Plinian case, which promotes faster ascent, closed-system degassing, fragmentation and explosive activity. In contrast, dome-forming phases are promoted by a higher magma viscosity due to higher phenocryst content, with slower ascent enhancing gas escape and microlite crystallization, decreasing explosivity and yielding effusive activity. Resumen Los estratovolcanes se caracterizan comúnmente por presentar actividad eruptiva cíclica, marcada por transiciones entre erupciones formadoras de domos y erupciones de tipo Vulcanianas, Subplinianas y Plinianas. El volcán Guagua Pichincha (Ecuador) ha dado lugar a tal ciclicidad durante los últimos ~ 2000 años, con erupciones Plinianas tanto en los siglos Primero y Décimo, como en el año 1660, las cuales estuvieron intercaladas por erupciones formadoras de domos y de tipo Subplinianas, tal como ocurrió durante la erupción reciente de 1999–2001. Estos ciclos son, por lo tanto, ejemplos destacados de transiciones eruptivas de tipo efusiva-explosiva a escalas de tiempo variadas. En este trabajo, investigamos las razones de tales cambios de actividad enfocándonos en procesos de exsolución y pérdida de gases del magma en el conducto (desgasificación en sistemas cerrado y abierto). Hemos acoplado análisis petrofísicos y texturales tanto de dacitas de la erupción Pliniana de 1660, como de la erupción formadora de domos/Vulcaniana de 1999–2001, junto con diferentes modelos de percolación, para así comprender mejor el rol de la exsolución de volátiles en el estilo eruptivo. Demostramos que la transición desde una actividad efusiva formadora de domos a una Pliniana está correlacionada con diferencias en el contenido de fenocristales y, subsecuentemente, con la viscosidad total del magma. Un contenido inicial menor de fenocristales y una menor viscosidad se infiere para el caso Pliniano, lo que promueve un ascenso más rápido, desgasificación en sistema cerrado, fragmentación y finalmente actividad explosiva. Por el contrario, las fases formadoras de domos son promovidas por una viscosidad mayor debido a un contenido mayor de fenocristales, con ascenso más lento promoviendo a su vez el escape de gases y la cristalización de microlitos, disminuyendo la explosividad y produciendo actividad efusiva.

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Section: Macroscopic Descriptionmentioning

confidence: 99%

Conduit processes in crystal-rich dacitic magma and implications for eruptive cycles at Guagua Pichincha volcano, Ecuador

et al. 2022

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“…The evolving grain-size distribution (GSD) of block-and-ash flows may provide such a mechanism. In column collapse PDCs, secondary fragmentation, or comminution, has led to measurable rounding differences and is linked to enhanced runout distances 34 – 37 . BAF deposits start as a mixture dominated by blocks (>64 mm) and transform into a blend of blocks immersed in fines-rich (<4 mm) matrix (Fig.…”

Section: Introductionmentioning

confidence: 99%

The fragmentation-induced fluidisation of pyroclastic density currents

et al. 2023

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Pyroclastic density currents (PDCs) are the most lethal volcanic process on Earth. Forecasting their inundation area is essential to mitigate their risk, but existing models are limited by our poor understanding of their dynamics. Here, we explore the role of evolving grain-size distribution in controlling the runout of the most common PDCs, known as block-and-ash flows (BAFs). Through a combination of theory, analysis of deposits and experiments of natural mixtures, we show that rapid changes of the grain-size distribution transported in BAFs result in the reduction of pore volume (compaction) within the first kilometres of their runout. We then use a multiphase flow model to show how the compressibility of granular mixtures leads to fragmentation-induced fluidisation (FIF) and excess pore-fluid pressure in BAFs. This process dominates the first ~2 km of their runout, where the effective friction coefficient is progressively reduced. Beyond that distance, transport is modulated by diffusion of the excess pore pressure. Fragmentation-induced fluidisation provides a physical basis to explain the decades-long use of low effective friction coefficients used in depth-averaged simulations required to match observed flow inundation.

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“…In fact, many eruptions from intermediate to high explosivity produce ash plumes and PDCs concomitantly (J. Bernard et al., 2016 ). Particles transported in PDCs have undergone a secondary fragmentation process (the primary fragmentation being that of the magma in the volcanic conduit) by comminution of bigger grains (grain‐to‐grain abrasion) during their transport (J. Bernard & Le Pennec, 2016 ; Buckland et al., 2018 ; Hornby et al., 2020 ). Understanding the origin of the inhalable ash fractions is thus essential, because secondary fragmentation could affect the size, morphology, and surface properties of the grains, which are relevant for toxicity.…”

Section: Discussionmentioning

confidence: 99%

Spatial Distribution and Physicochemical Properties of Respirable Volcanic Ash From the 16–17 August 2006 Tungurahua Eruption (Ecuador), and Alveolar Epithelium Response In‐Vitro

et al. 2022

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Tungurahua volcano (Ecuador) intermittently emitted ash between 1999 and 2016, enduringly affecting the surrounding rural area and its population, but its health impact remains poorly documented. We aim to assess the respiratory health hazard posed by the 16-17 August 2006 most intense eruptive phase of Tungurahua. We mapped the spatial distribution of the health-relevant ash size fractions produced by the eruption in the area impacted by ash fallout. We quantified the mineralogy, composition, surface texture, and morphology of a respirable ash sample isolated by aerodynamic separation. We then assessed the cytotoxicity and pro-inflammatory potential of this respirable ash towards lung tissues in-vitro using A549 alveolar epithelial cells, by electron microscopy and biochemical assays. The eruption produced a high amount of inhalable and respirable ash (12.0-0.04 kg/m2 of sub-10 µm and 5.3-0.02 kg/m2 of sub-4 µm ash deposited). Their abundance and proportion vary greatly across the deposit within the first 20 km from the volcano. The respirable ash is characteristic of an andesitic magma and no crystalline silica is detected. Morphological features and surface textures are complex and highly variable, with few fibres observed. In-vitro experiments show that respirable volcanic ash is internalized by A549 cells and processed in the endosomal pathway, causing little cell damage, but resulting in changes in cell Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site.morphology and membrane texture. The ash triggers a weak pro-inflammatory response. These data provide the first understanding of the respirable ash hazard near Tungurahua and the extent to which it varies spatially in a fallout deposit. Key Points► The 16-17 August 2006 Tungurahua eruption produced a high amount of inhalable (12.0-0.04 kg/m2 of sub-10 µm deposited on the ground) and respirable ash (5.3-0.02 kg/m2 of sub-4 µm ash deposited on the ground). The abundance and proportion of inhalable and respirable ash vary greatly across the deposit within the first 20 km from the volcano ► The respirable ash is characteristic of an andesitic magma and no crystalline silica is detected. Morphological features and surface textures are complex and highly variable, with few fibres observed ► In-vitro experiments show that respirable volcanic ash is internalized by A549 cells and processed in the endosomal pathway, causing little cell damage, but resulting in changes in cell morphology and membrane texture. The ash triggers a weak pro-inflammatory response Plain Language SummaryMuch is left to understand on the health hazard related to inhaling volcanic ash. This is due to the high variability in ash properties from one volcanic eruption to another. In our new study, we focus on a key volcanic environment, the region of Tungurahua volcano in the Eastern Andean Cordillera of Ecuador, where populations were affected by an ex...

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Experimental constraints on volcanic ash generation and clast morphometrics in pyroclastic density currents and granular flows

Cited by 16 publications

References 78 publications

Conduit processes in crystal-rich dacitic magma and implications for eruptive cycles at Guagua Pichincha volcano, Ecuador

Conduit processes in crystal-rich dacitic magma and implications for eruptive cycles at Guagua Pichincha volcano, Ecuador

The fragmentation-induced fluidisation of pyroclastic density currents

Spatial Distribution and Physicochemical Properties of Respirable Volcanic Ash From the 16–17 August 2006 Tungurahua Eruption (Ecuador), and Alveolar Epithelium Response In‐Vitro

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