28 research outputs found

    VOLCANS: an objective, structured and reproducible method for identifying sets of analogue volcanoes

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    The definition of a suite of analogue volcanoes, or volcanoes that are considered to share enough characteristics as to be considered exchangeable to a certain extent, is becoming a key component of volcanic hazard assessment. This is particularly the case for volcanoes where data are lacking or scarce. Moreover, volcano comparisons have often been based on similarities and differences inferred through expert judgement and not necessarily informed by volcano characteristics from global datasets. These similarities can be based on a range of features, from very simplified (e.g. statrovolcanoes) to very specific (e.g. detailed eruption chronologies), and may be strongly influenced by the personal experience of individuals or teams conducting the analogue analysis. In this work, we present VOLCANS (VOLCano ANalogues Search)—an objective, structured and reproducible method to identify sets of analogue volcanoes from global volcanological databases. Five overarching criteria (tectonic setting, rock geochemistry, volcano morphology, eruption size and eruption style), and a structured combination of them, are used to quantify overall multi-criteria volcano analogy. This innovative method is complementary to expert-derived sets of analogue volcanoes and provides the user with full flexibility to weigh the criteria and identify analogue volcanoes applicable to varied purposes. Some results are illustrated for three volcanoes with diverse features and significant recent and/or ongoing eruptions: Kı̄lauea (USA), Fuego (Guatemala) and Sinabung (Indonesia). The identified analogue volcanoes correspond well with a priori analogue volcanoes derived from expert knowledge. In some cases, single-criterion searches may not be able to isolate a reduced set of analogue volcanoes but any multi-criteria search can provide high degrees of granularity in the sets of analogue volcanoes obtained. Data quality and quantity can be important factors, especially for single-criterion searches and volcanoes with very scarce data (e.g. Sinabung). Nevertheless, the method gives stable results overall across multi-criteria searches of analogue volcanoes. Potential uses of VOLCANS range from quantitative volcanic hazard assessment to promoting fundamental understanding of volcanic processes

    Rhyolite lava dome growth styles at Chaitén Volcano, Chile (2008-2009):Interpretation of thermal imagery

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    Artículo de publicación ISIAirborne thermal images of the Chaitén rhyolite lava dome were obtained on three occasions between January 2009 and January 2010. These images were useful for understanding the nature and pace of growth of the newly extruded lava, which formed a complex of lobes and a spine. The images also revealed contrasting growth styles affecting different parts of the lava dome complex. Observed synchronous endogenous and exogenous growth was likely the result of multiple flow paths within the lava dome. We suggest that contrasts in morphology and surface texture between various lava lobes are the result of different extrusion rates

    The association of lava dome-growth with major explosive activity (VEI≥ 4): DomeHaz, a global dataset

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    Investigation of the global eruptive records of particular types of volcanoes is a fundamental and valuable method of understanding what style of activity can be anticipated in the future and can highlight what might be expected or unusual in particular settings. This paper investigates the relationship between large explosions (volcanic explosivity index, VEI ≥ 4) and lava dome growth from 1000 AD to present and develops the DomeHaz database. DomeHaz contains information from 397 dome-forming episodes, including duration of dome growth, duration of pauses in extrusion, extrusion rates, and the timing and magnitude (VEI) of associated large explosions. Major explosive activity, when associated with dome growth, is more likely to occur before dome growth rather than during, or at the end of, dome-forming eruptions. In most cases where major explosive activity has been associated with dome growth, the eruptions occurred at basaltic andesite to andesitic volcanoes (the most common type of dome-forming volcano), but a greater proportion of dacitic and rhyolitic dome growth episodes were associated with large explosions. High extrusion rates (>10 m3 s−1) seem to be associated with large explosions and may inhibit degassing or destabilize existing domes, leading to explosive decompression. Large explosions may, alternatively, be followed by dome growth, which represents the clearing of residual magma from the conduit. Relationships extracted from the global record can be used to construct probability trees for new and ongoing dome-forming eruptions or can be used in conjunction with other types of event trees to aid in forecasting volcanic hazards during a crisis, especially for volcanoes where data are sparse

    The hydrothermal alteration of cooling lava domes

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    Correlations between SO2 flux, seismicity, and outgassing activity at the open vent of Villarrica volcano, Chile

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    The characteristics of the open vent activity of Villarrica volcano, Chile, were studied in detail by integrating visual observations of the lava lake, analysis of the seismic tremor, and measurements of SO2 flux. The outgassing activity comprises a persistent gas plume emission from the bottom of the crater as well as frequent explosive events. Three main styles of bubble bursting were identified at the surface of the active lava lake: seething magma, small short-lived lava fountains, and Strombolian explosions. Seething magma consists of continual burst of relatively small bubbles (a few meters in diameter) with varying strength over the entire surface of the lava lake. Small lava fountains, seen as a vigorous extension of seething magma, commonly have durations of 20–120 s and reach 10–40 m high above the lava lake. Correlations between seismicity and visual observations indicate that the seismic tremor is mostly caused by the explosive outgassing activity. Furthermore, for different periods between 2000 and 2006, during which the activity remained comparable, the real-time seismic amplitude measurement system (RSAM) and SO2 emission rates show a very good correlation. Higher SO2 emissions appeared to be related to higher levels of the lava lake, stronger bubble bursting activity, and changes in the morphology and texture of the crater floor. Background (low) levels of activity correspond to a lava lake located >80 m below the crater rim, small and/or blocky morphology of the roof, seismic amplitude (RSAM) lower than 25 units, few volcano-tectonic earthquakes, and daily averages of SO2 emissions lower than 600 Mg/d

    Textural and geochemical constraints on andesitic plug emplacement prior to the 2004–2010 vulcanian explosions at Galeras volcano, Colombia

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    Hazardous sequences of vulcanian explosions are thought to result from the repeated emplacement and destruction of degassed, highly crystalline magma plugs in the shallow conduit of arc volcanoes. The processes governing the timing and magnitude of these explosions are thought to be related to magma ascent rate and efficiency of degassing and crystallisation. We study a rare suite of time-constrained ballistic bombs from the 2004–2010 period of activity of Galeras volcano to reconstruct magma plug architecture prior to six individual vulcanian explosions. We find that each plug was vertically stratified with respect to crystallinity, vesicularity and melt volatile content, melt composition and viscosity. We interpret this structure as resulting from multiple bubble nucleation events and degassing-driven crystallisation during multi-step ascent of the magma forming the plug, followed by spatially variable crystallisation within the plug under contrasting conditions of effective undercooling created by degassing. We propose that the shallow conduit evolved from more open degassing conditions during 2004–2008 to more closed conditions during 2009–2010. This resulted in explosions becoming smaller and less frequent over time during 2004–2008, then larger and more frequent over time during 2009–2010. This evolution was controlled by changing average ascent rates and is recorded by systematic changes in plagioclase microlite textures. Our results suggest that small volume vulcanian explosions (~ 105 m3) should generally be associated with longer repose times (hundreds of days) and produce ballistics characterised by small numbers of large, prismatic plagioclase microlites. Larger volume vulcanian explosions (~ 106 m3) should be associated with shorter repose times (tens of days) and produce ballistics characterised by high numbers of small, more tabular plagioclase microlites
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