Under the surface: Textural analysis of complex, multi-component Vulcanian bombs produced during the hybrid effusive-explosive phase of the 2011-2012 Cordón Caulle eruption, Chile

<p>The ascent, eruption, and deposition of volcanic pyroclasts is complex, but the resultant rocks have distinctive textural markers that indicate the unseen processes that were operating during a given eruption. These textures can be used to build a picture of the sequence of events and the eruptive environment. Vulcanian eruptions, short-lived, intermittent blasts interpreted as the clearing of a conduit plug, produce ballistic pyroclasts with textures that are directly correlated with the makeup of the plug material. A late phase of the recent eruption of Puyehue-Cordón Caulle (2011-2012, Southern Chile) produced a striking array of, colourful, and texturally diverse Vulcanian bombs. The eruption began on June 4th 2011 with Plinian to Sub-Plinian activity, transitioning to a phase of obsidian lava effusion on June 15th, and then to a hybrid effusive-explosive phase (vulcanian bomb ejection coeval with an effusive obsidian lava flow) in January 2012. Transitions from explosive to effusive activity are often described as singular, definitive, one-way events, at odds with the hybrid effusive-explosive activity seen at Puyehue-Cordón Caulle. Textures in these bombs indicate that the constituent melts have experienced several (possibly countless) episodes of fragmentation, sintering, densification, shearing, and vesiculation within a conduit-scale breccia pack, conceptually equivalent to a conduit-scale tuffisite vein. In all examined bombs, centimetre to micron scale clasts of basaltic-andesite (~SiO2 54-55 wt%) are found, with textures that indicate a magmatic origin. Although volumetrically minor, co-mingling of a hotter, mafic magmatic component has implications for the anomalously hot rhyolite, as well as the onset and longevity of the hybrid eruption phase. Textural and geochemical characteristics of bombs elucidate complex processes in the shallow conduit and vent, advancing the understanding of tuffisite veins and Vulcanian eruption dynamics, which are far from straightforward.</p>

Under the surface: Textural analysis of complex, multi-component Vulcanian bombs produced during the hybrid effusive-explosive phase of the 2011-2012 Cordón Caulle eruption, Chile

<p>The ascent, eruption, and deposition of volcanic pyroclasts is complex, but the resultant rocks have distinctive textural markers that indicate the unseen processes that were operating during a given eruption. These textures can be used to build a picture of the sequence of events and the eruptive environment. Vulcanian eruptions, short-lived, intermittent blasts interpreted as the clearing of a conduit plug, produce ballistic pyroclasts with textures that are directly correlated with the makeup of the plug material. A late phase of the recent eruption of Puyehue-Cordón Caulle (2011-2012, Southern Chile) produced a striking array of, colourful, and texturally diverse Vulcanian bombs. The eruption began on June 4th 2011 with Plinian to Sub-Plinian activity, transitioning to a phase of obsidian lava effusion on June 15th, and then to a hybrid effusive-explosive phase (vulcanian bomb ejection coeval with an effusive obsidian lava flow) in January 2012. Transitions from explosive to effusive activity are often described as singular, definitive, one-way events, at odds with the hybrid effusive-explosive activity seen at Puyehue-Cordón Caulle. Textures in these bombs indicate that the constituent melts have experienced several (possibly countless) episodes of fragmentation, sintering, densification, shearing, and vesiculation within a conduit-scale breccia pack, conceptually equivalent to a conduit-scale tuffisite vein. In all examined bombs, centimetre to micron scale clasts of basaltic-andesite (~SiO2 54-55 wt%) are found, with textures that indicate a magmatic origin. Although volumetrically minor, co-mingling of a hotter, mafic magmatic component has implications for the anomalously hot rhyolite, as well as the onset and longevity of the hybrid eruption phase. Textural and geochemical characteristics of bombs elucidate complex processes in the shallow conduit and vent, advancing the understanding of tuffisite veins and Vulcanian eruption dynamics, which are far from straightforward.</p>

Influence of Hydrothermal Recharge on the Evolution of Eruption Styles and Hazards During the 2018–2019 Activity at Kuchinoerabujima Volcano, Japan

The activity of the 2018-2019 eruption of Kuchinoerabujima Volcano in Japan changed from continuous ejection of ash-laden plumes between October 21 and the middle of December, to intermittent explosive activity accompanied by several pyroclastic density currents until January 2019. To understand the behaviors of magma and hydrothermal fluid that controlled the eruptive sequence, we carried out component analysis, X-ray diffractometry, and leachate analysis for ash samples. The proportion of non-altered volcanic ash particles is ~15 % in the earlier phase, then it decreased to less than 10 % in the later explosive phase. Accordingly, the mineral assemblage of the volcanic ash samples changed from plagioclase-dominant to sulfate minerals-dominant. Concentration of SO42- and Cl/SO4 values of the ash-leachates decreased toward the later activity. These results indicate that the proportion of fresh volcanic rocks decreased and sulfuric acid fluid-derived sulfate minerals increased toward the later activities. Consequently, the 2018-2019 eruption at Kuchinoerabujima Volcano changed from magmatic activity to phreatomagmatic activity. Weak glowing of the crater was observed during the magmatic activity, indicating the volcanic conduit was hot enough to dry up the subvolcanic hydrothermal system. The following phreatomagmatic activity indicates that the hydrothermal fluid recharged after the magmatic eruption phase. Recharge of the hydrothermal fluid likely caused the variation of the eruption style, and is a process that may control the evolution of hazards during future eruption scenarios at similar active volcanoes in Japan and worldwide.

Volcanic tremor of the 2010 Eyjafjallajökull eruption

Summary Volcanic eruptions in Iceland generally start with an increase in tremor levels. These signals do not have clear onset, like many earthquakes. As the character of the tremor signal is variable from one volcano to another, locating the source of the tremor signal may require different techniques for different volcanoes. Continuous volcanic tremor varied considerably during the course of the Eyjafjallajökull summit eruption, April 14th to May 22nd 2010, and was clearly associated with changes in eruptive style. The tremor frequencies ranged between 0.5 and 10 Hz, with increased vigour during an effusive and explosive phase, in comparison with purely explosive phases. Higher-frequency tremor bursts early in the eruption were caused by processes at the eruption site. Location of the tremor using a method based on differential phase information extracted from inter-station correlograms showed the tremor to be stable near the eruption vent, through time, for signals between 0.5 Hz and 2 Hz. Analyses of power variations of the vertical component of the tremor with distance from the eruption site are consistent with tremor waveform content being dominated by surface waves in the 0.5-2 Hz frequency range. The tremor source depth was argued to be shallow, less than about 1 km. The attenuation quality factor (Q) was found to be on the order of Q = 10-20 for paths in the area around Eyjafjallajökull and Q = 20-50 for paths outside the volcano. The pattern of radiated wave energy from the tremor source varied with time, defining ten different epochs during the eruption. Thus the tremor-source radiation did not remain isotropic, which needs to be considered when locating tremor based on amplitude, i.e. azimuthally variable source radiation.

Rapid eruptive transitions from low to high intensity explosions and effusive activity: insights from textural analysis of a small-volume trachytic eruption, Ascension Island, South Atlantic

Proximal deposits of small-volume trachytic eruptions are an under-studied record of eruption dynamics despite being common across a range of settings. The 59 ± 4 ka Echo Canyon deposits, Ascension Island, resulted from a small-volume explosive-effusive trachytic eruption. Variations in juvenile clast texture reveal changes in ascent dynamics and transitions in eruption style. Five dominant textural types are identified within the pumice lapilli population. Early Strombolian-Vulcanian eruption phases are typified by macro- and micro-vesicular equant clast types. Sheared clasts are most abundant at the eruption peak, transitioning to dense clasts in later phases due to shear-induced coalescence, outgassing and vesicle collapse. Melt densification and outgassing via tuffisite veins increased plume density, contributing to partial column collapse and the explosive-effusive transition. Bulk vesicularity distributions indicate a shift in dominant fragmentation mechanism during the eruption, from early-stage bubble interference and rupture to late-stage transient fragmentation, with a transient peak of Plinian activity. Dome and lava groundmass crystallinities of up to 70% indicate near-complete degassing during effusive phases, followed by shallow over pressurisation and a final less explosive phase. We provide textural evidence for high-intensity explosive phases and rapid transitions in eruptive style during small-volume trachytic eruptions and consider the impact of trachytic melt compositions on underlying dynamics of these short-lived, explosive events. This analysis demonstrates the value of detailed stratigraphy in understanding critical changes in eruption dynamics and the timescales over which they may occur which is of particular value in anticipating future eruptions of this type.

Continuous monitoring of SO2 emissions from Sinabung Volcano, Indonesia

&lt;p&gt;After more than 800 years of dormancy, phreatic explosions occurred at Sinabung Volcano in North Sumatra, Indonesia, on August 27, 2010. These marked the beginning of a period of unrest at Sinabung that continues through the present. Phreatic activity temporarily ceased in September 2010, however a more explosive phase of the eruption began again in September 2013, sending ash columns as high as 9 km above the volcano&amp;#8217;s summit. A lava dome breached the surface on 17-18 December 2013 and subsequent collapses of this dome have produced numerous pyroclastic density currents reaching up to 5 km from the vent. Eruptive activity has waxed and waned since 2013, and the eruption entered period of especially vigorous activity beginning in February 2019 that is continuing through the present.&lt;/p&gt;&lt;p&gt;Between 2010 and 2013, the Indonesian Center for Volcanology and Geological Hazard Mitigation (CVGHM) significantly ramped up its monitoring efforts at Sinabung by installing seismometers, GPS instruments and electronic distance measuring benchmarks. In August 2016, the volcano observatory then installed a network of 3 scanning Differential Optical Absorption Spectrometers (DOAS) on the eastern side of Sinabung at distances between 4 and 6 km from the volcano&amp;#8217;s summit. These DOAS instruments are part of the Network for Observation of Volcanic and Atmospheric Change (NOVAC), and autonomously measure the emission rate of sulfur dioxide (SO&lt;sub&gt;2&lt;/sub&gt;) from Sinabung during typical west-wind conditions.&lt;/p&gt;&lt;p&gt;Since its installation, the DOAS network has provided useful monitoring information at Sinabung. The collected data indicate that the average SO&lt;sub&gt;2&lt;/sub&gt; emission rate lies between 100 and 400 metric tons per day (t/d), but emissions up to 2,400 t/d are common throughout the measurement period. The maximum emission rate recorded since 2016 was 4,500 t/d, measured in July 2019. However, the NOVAC instruments are not able to accurately capture the SO&lt;sub&gt;2&lt;/sub&gt; emissions associated with large explosive eruptions, and satellite data indicate that plumes associated with such events have sometimes contained significantly more SO&lt;sub&gt;2&lt;/sub&gt; than during the more typical passive degassing behavior. Here, we present excerpts of the long-term SO&lt;sub&gt;2&lt;/sub&gt; data from Sinabung and compare these with complimentary records of the timing and frequency of explosions, gas exhalations, rockfalls, and pyroclastic flows. These combined datasets provide insights into the active volcanic processes ongoing at Sinabung.&lt;/p&gt;

Basic Volcanic Elements of the Arxan-Chaihe Volcanic Field, Inner Mongolia, NE China

The Arxan-Chaihe Volcanic Field, Inner Mongolia, NE China is a Pleistocene to Recent volcanic field still considered to be active. In this chapter we provide an update of current volcanological research conducted in the last four years to describe the volcanic architecture of the identified vents, their eruptive history and potential volcanic hazards. Here we provide an evidence-based summary of the most common volcanic eruption styles and types the field experienced in its evolution. The volcanic field is strongly controlled by older structural elements of the region. Hence most of the volcanoes of the field are fissure-controlled, fissure-aligned and erupted in Hawaiian to Strombolian-style creating lava spatter and scoria cone cone chains. One of the largest and most complex volcano of the field (Tongxin) experienced a violent phreatomagmatic explosive phase creating a maar in an intra-mountain basin, while the youngest known eruptions formed a triple vent set (Yanshan) that reached violent Strombolian phases and created an extensive ash and lapilli plains in the surrounding areas. This complex vent system also emitted voluminous lava flows that change the landscape by damming fluival networks, providing a volcanological paradise for the recently established Arxan UNESCO GLobal Geopark.

La Performance in Italia tra ‘comportamenti’ esplosivi ed implosivi

The essay examines a short period of the performance art phenomenon, or art of behavior, between 1967 and the mid 70s, a period characterized by an euphoric, explosive phase followed by an implosive, analytical moment that gave up unconventional spaces in favour of those traditionally exhibited. Considering critical points of view of foreign scholars, the essay questions the peculiarities that define an Italian and "Roman" identity (Fabio Mauri, Luca Patella, Vettor Pisani, Gino De Dominicis, Jannis Kounellis…) of the phenomenon that the author traces in the interdisciplinary nature, in the use of technological media, of mythology, art history, alchemical symbols, in the irony that attacks the role of the artist and above all in the constant reference to painting.

Mechanisms controlling explosive-effusive transition of Teide-Pico Viejo complex dome eruptions.

&lt;p&gt;The Teide-Pico Viejo (PT-PV) stratovolcanoes constitute one of the major potentially active volcanic complexes in Europe. PT-PV was traditionally considered as non-explosive system however, recent studies (ie. Garc&amp;#237;a et al. 2014) have pointed out that the explosive character of phonolitic magmas, including plinian and subplinian eruptions and generation of pyroclastic density currents, have also been significant within the last 30 kyr volcanological record. This explosive activity is mostly associated to satellite dome vents, like the one studied in this work, Pico Cabras. Dome-forming eruptions usually present sudden transitions between explosive and effusive activity. A better knowledge of this type of eruptions and about the main mechanisms controlling the changes in eruptive dynamics is required to undertake a comprehensive volcanic hazard assessment of Tenerife Island. In this study, we conduct a petrological and mineral characterization of the different eruption phases of Pico Cabras (pumice and lava flow samples for the explosive and effusive activity, respectively) with the aim of determining the factors that control these changes in the volcanic activity. Products were characterized with Scanning Electrom Microscope, and mineral phases, glass and volatile species (F, Cl) were analysed with electron microprobe and micro-XRF. The pre-eruptive conditions of the magma (pressure, temperature and water dissolved in the magma) were determined first by using available geothermobarometers, geohygrometers (Masotta et al., 2013; Mollo et al., 2015) and compared to those retrieved by using available phase equilibria experiments from the literature (ie. And&amp;#250;jar and Scaillet, 2012).&lt;/p&gt;&lt;p&gt;Our results suggest the presence of a compositionally stratified magma chamber at 1 kbar&amp;#177;0.5kbar prior to Pico Cabras eruption in which the differences in the eruptive styles are controlled by the temperature and the amount of volatiles dissolved in the melt. The explosive phase is related to the upper part of the magma chamber at 725&amp;#186;C&amp;#177;25&amp;#186;C and 3,5-5 wt% H&lt;sub&gt;2&lt;/sub&gt;O and the effusive phase with the main body of the chamber at 880&amp;#186;C&amp;#177;30&amp;#186;C and 2,5-3 wt% H&lt;sub&gt;2&lt;/sub&gt;O. Feldspar zonations show that overturn events occurred in the different layers of the magma chambers (&amp;#8220;self-mixing&amp;#8221;) and suggest that the eruption was triggered by underplating of mafic magma without magma mixing. Chemical composition of some feldspars from the explosive phase are equivalent to those found in El Abrigo eruption, the last caldera-forming episode (ca. 190 ka), demonstrating that PT-PV volcanic system is still capable of producing evolved and very explosive magmas.&lt;/p&gt;&lt;p&gt;This research has been partially funded by a CSIC JaeIntro grant and the EC Grant EVE (DG ECHO Ref: 826292).&lt;/p&gt;