Explosive volcanism

Keywords: explosive basaltic volcanism Olot NE Spain SEM description card eruptive mechanisms strombolian phreatomagmatic An ephemeral (and proximal) outcrop at the quaternary basaltic Puig de la Garrinada cinder volcano was studied in order to decipher eruptive mechanism variations in the course of a single eruption. Once the volcanostratigraphy was established (and recorded by photographs), a very detailed sampling of underlying lava flows, bombs and a large number of fine-sized lapilli and ash beds was carried out. An ad hoc description card was elaborated for study under stereo microscope in order to identify the different types of materials that form the volcanic cone. Ten material types were recognised: sedimentary accidental clasts, massive lava accidental clasts, bombs, xenoliths, xenocrysts and phenocrysts, oxidised scoria, scoria with oxidised film, fluidal pyroclasts, non-fluidal pyroclasts, and coatings. Subsequent studies under SEM + EDS and basic chemical characterization of the samples (whole rock XRF for major and trace elements) and EMPA were conducted. All these studies make possible the reconstruction of the eruptive history of the La Garrinada volcano, which shows a transition from initial strombolian activity to gradually incorporated phreatomagmatic activity. This permits the calculation of magma eruption rates, magma column oscillations and aquifer interactions with magma column. Since our general conclusions agree well with the discrimination of eruptive episodes obtained from the stereo microscope description card, macroscopic volcanostratigraphy and chemical results, it is proposed that a similar study protocol (quick volcanostratigraphy logging, photographic record, detailed sampling, description following this card) might be useful in the reconstruction of eruptive activity of other cinder cones in the Garrotxa region and elsewhere, and therefore can provide a good and quick methodological tool, especially when rapid field description and sampling is required (ephemeral outcrops, risky sampling during active eruptive episodes, etc.). Moreover, the conducted sampling allows for subsequent studies on the same set of pyroclasts.

An ephemeral (and proximal) outcrop at the quaternary basaltic Puig de la Garrinada cinder volcano was
studied in order to decipher eruptive mechanism variations in the course of a single eruption. Once the
volcanostratigraphy was established (and recorded by photographs), a very detailed sampling of underlying
lava flows, bombs and a large number of fine-sized lapilli and ash beds was carried out. An ad hoc description
card was elaborated for study under stereo microscope in order to identify the different types of materials
that form the volcanic cone. Ten material types were recognised: sedimentary accidental clasts, massive lava
accidental clasts, bombs, xenoliths, xenocrysts and phenocrysts, oxidised scoria, scoria with oxidised film,
fluidal pyroclasts, non-fluidal pyroclasts, and coatings. Subsequent studies under SEM+EDS and basic
chemical characterization of the samples (whole rock XRF for major and trace elements) and EMPA were
conducted. All these studies make possible the reconstruction of the eruptive history of the La Garrinada
volcano, which shows a transition from initial strombolian activity to gradually incorporated phreatomagmatic
activity. This permits the calculation of magma eruption rates, magma column oscillations and aquifer
interactions with magma column. Since our general conclusions agree well with the discrimination of
eruptive episodes obtained from the stereo microscope description card, macroscopic volcanostratigraphy
and chemical results, it is proposed that a similar study protocol (quick volcanostratigraphy logging,
photographic record, detailed sampling, description following this card) might be useful in the
reconstruction of eruptive activity of other cinder cones in the Garrotxa region and elsewhere, and therefore
can provide a good and quick methodological tool, especially when rapid field description and sampling is
required (ephemeral outcrops, risky sampling during active eruptive episodes, etc.). Moreover, the conducted
sampling allows for subsequent studies on the same set of pyroclasts.

Ilopango volcano (El Salvador) erupted violently during the Maya Classic Period (250e900 CE) in a densely-populated and intensively-cultivated region of the southern Maya realm, causing regional abandonment of an area covering more than 20,000 km 2. However, neither the regional nor global impacts of the Tierra Blanca Joven (TBJ) eruption in Mesoamerica have been well appraised due to limitations in available volcanological, chronological, and archaeological observations. Here we present new evidence of the age, magnitude and sulfur release of the TBJ eruption, establishing it as one of the two hitherto unidentified volcanic triggers of a period of stratospheric aerosol loading that profoundly impacted Northern Hemisphere climate and society between circa 536 and 550 CE. Our chronology is derived from 100 new radiocarbon measurements performed on three subfossil tree trunks enveloped in proximal TBJ pyroclastic deposits. We also reassess the eruption magnitude using terrestrial (El Salvador, Guatemala, Honduras) and near-shore marine TBJ tephra deposit thickness measurements. Together, our new constraints on the age, eruption size (43.6 km 3 Dense Rock Equivalent of magma, magnitude ¼ 7.0) and sulfur yield (~9e90 Tg), along with Ilopango's latitude (13.7 N), squarely frame the TBJ as the major climate-forcing eruption of 539 or 540 CE identified in bipolar ice cores and sourced to the tropics. In addition to deepening appreciation of the TBJ eruption's impacts in Mesoamerica, linking it to the major Northern Hemisphere climatic downturn of the mid-6th century CE offers another piece in the puzzle of understanding Eurasian history of the period.

Kamafugites are rare and it is recognized on the border between Uganda and Zaire (Africa), Italy and Brazil. Other rocks with kamafugitic affinity occur in China, Turkey and Serbia. In Brazil, vulcanism of kamafugitic rocks occurs in Goiás, in the Goiás Alkaline Province (GAP) and in Minas Gerais, in the Alto Paranaíba Igneous Province (APIP). The target area of work is the southern region of GAP, more specifically in Santo Antônio da Barra and Rio Verde, where are the places that there are extensive volcanic and pyroclastic expositions of kamafugites. This rock dates from the Upper Cretaceous and there are different hypotheses for their genesis, such as through mantle plumes and extensive activities (rifts). The kamafugitic rocks of Rio Verde and Santo Antônio da Barra, in hand sample, are light gray, dark gray and black. They have a massive structure and more rarely a magmatic flow structure marked by the orientation of pyroxene phenocrysts. They are phaneritic, with aphanitic matrix and phenocrysts of piroxene, olivine, leucite and / or analcimes and carbonates. Some lava rocks have many vesicles that sometimes can be filled with by carbonates, zeólitas or clay minerals. There are pyroclastic rocks that are mixed or partially over the lava rocks. Pyroclastic rocks sometimes host blocks of other rocks. Microscopically, there are holocrystalline and hypocrystalline rocks. They are inequigranular porphyritic with glomereroporphyrytic texture and some with vesicular and amygdaloidal texture. The minerals present in these rocks, in general, are: clinopyroxene, olivine, leucite, analcime, carbonate, kalsilite / nepheline, apatite and titanobiotite. There are other minerals that have not been defined that fill the vesicles, matrix’s interstices and veins. The vesicular and amygdaloidal textures and the presence of pyroclastic rocks with fragments of other rocks may indicate that the magma generator was rich in volatiles and that the volcanism was explosive.

Sacrofano eruptive center, in the eastern part of the Sabatini volcanic complex, was active between 0.5 and 0.09 m.y. ago. The Baccano geothermal area lies at the western edge of Sacrofano caldera. Sedimentary substrata that form the reservoir for this geothermal system were exposed at the surface at the beginning of volcanic activity. The volcanic history of the Sacrofano center can be divided into three stages: (1) Construction of the Sacrofano pyroclastic edifice by predominantly Strombolian activity. (2) Collapse of Sacrofano caldera following eruption of pyroclastic flows. (3) Development of the Baccano explosive center at the western edge of Sacrofano caldera and collapse of Baccano caldera. Hydrovolcanic activity that began at the end of the first stage of Sacrofano can be explained by a drop in the magma level in the conduit that relieved hydrostatic pressure in the aquifer. As intense fracturing associated with caldera collapse penetrated the carbonate reservoir, the entrapped water flowed towards the conduit to balance the pressure change. The close link between tectonism and volcanism in the Sacrofano center suggests that eruptions there may have been triggered by gravity faults related to regional tectonics.

The Croscat pyroclastic succession has been analysed to investigate the transition between different eruptive
styles in basaltic monogenetic volcanoes, with particular emphasis on the role of phreatomagmatism in
triggering Violent Strombolian eruptions. Croscat volcano, an 11 ka basaltic complex scoria cone in the
Quaternary Garrotxa Volcanic Field (GVF) shows pyroclastic deposits related both to magmatic and
phreatomagmatic explosions.
Lithofacies analysis, grain size distribution, chemical composition, glass shard morphologies, vesicularity,
bubble-number density and crystallinity of the Croscat pyroclastic succession have been used to characterize
the different eruptive styles. Eruptions at Croscat began with fissural Hawaiian-type fountaining that rapidly
changed to eruption types transitional between Hawaiian and Strombolian from a central vent. A first
phreatomagmatic phase occurred by the interaction between magma and water from a shallow aquifer
system at the waning of the Hawaiian- and Strombolian-types stage. A Violent Strombolian explosion then
occurred, producing a widespread (8 km2), voluminous tephra blanket. The related deposits are
characterized by the presence of wood-shaped, highly vesicular scoriae. Glass-bearing xenoliths (buchites)
are also present within the deposit. At the waning of the Violent Strombolian phase a second
phreatomagmatic phase occurred, producing a second voluminous deposit dispersed over 8.4 km2. The
eruption ended with a lava flow emission and consequent breaching of the western-side of the volcano. Our
data suggest that the Croscat Violent Strombolian phase was related to the ascent of deeper, crystal-poor,
highly vesicular magma under fast decompression rate. Particles and vesicles elongation and brittle failure
observed in the wood-shaped clasts indicate that fragmentation during Violent Strombolian phase was
enhanced by high strain-rate of the magma within the conduit

EXTENDED ABSTRACT
Tephrology of the 1932 eruption of the Quizapú volcano in the region of Laguna Llancanelo, Payenia (Mendoza, Argentina)
Tephrology is a broad term that comprises all the aspects related to “tephra” studies (stratigraphy, chronology, petrology, sedimentology, chemistry, Froggat and Lowe, 1990; Lowe and Hunt, 2001) (Fig. 1). In Argentina, tephrological studies have significantly increased recently as a result of the increment in the Southern Andes volcanic activity affecting the country in the last two decades (E.g.: Corbella et al., 1991a,b; Stern, 1991; Mazzoni and Destéfano, 1992; Nillni et al., 1992; Gonzalez Ferrán, 1993; Naranjo et al., 1993; Scasso et al., 1994; Nillni and Bischene, 1995; Haberle and Lumley, 1998; Villarosa et al., 2002; Kilian et al., 2003; Naranjo and Stern, 2004; Orihashi et al., 2004; Stern, 2004; Scasso and Carey, 2005; Daga et al., 2008; Watt et al., 2009; Martin et al., 2009; Leonard et al., 2009; Rovere et al., 2009, 2011; Wilson et al., 2009, 2012). The eruption of Quizapú volcano (Volcanic Complex Azul-Descabezado Grande, Province of Talca, Chile, 36,67°S-70,77°W, maximum height of 3788 m a.s.l.), that occurred on April 10, 1932, represented one of the largest eruptions worldwide in the 20th Century. It affected extensive regions of Argentina as well as many coastal areas of the Southwestern Atlantic Ocean as a result of the prevailing westerly winds, and specifically impacted dramatically in regions located nearby the source volcano (Department of Malargüe, Province of Mendoza, west-central Argentina).  The wide spreading of the resulting tephras and its easy reconnaissance in the field provides a great opportunity for detailed studies about the eruption and its products. Results on the eruptive aspects and tephras dispersion and deposition from this eruption were published by some authors (Lunkenheimer, 1932; Kittl, 1933; Walker, 1981, Hildreth and Drake, 1992, González Ferrán, 1993; Ruprecht and Bachmann, 2010; Ruprecht et al., 2012). In this contribution the sedimentological, mineralogical and chemical characteristics of the tephra deposits occurring at the Llancanelo Lake and surroundings, located 140 km east (downwind) of the Quizapú volcano, are studied based on grain-size, petrographic and electron microscope analysis (SEM) as well as semiquantitative chemical determinations by Energy Dispersive Spectrometer (EDS). The obtained results, when compared with the results of analyses performed by other authors in tephras from the 1932 eruption of the Quizapú volcano, allow attributing the studied tephra layer to this eruption. On these bases, diverse aspects related to the depositional and post-depositional aspects of the tephras are herein discussed, as well as some environmental changes produced by the eruption. On the other hand, this paper contributes to a systematic and comparative classification of volcanic hazard in health and society that serves as base-studies for better understanding other more recent Southern Andes eruptive events that affected Argentina (Hudson, Copahue, Chaitén, Llaima, Peteroa and Puyehue-Cordón Caulle volcanoes). The eruption of Quizapú volcano in 1932 was one of the most important events among a long history of activity of this volcanic complex (Smithsonian Institution, 2012). It had a plinian character and threw into the atmosphere enormous amounts of tephras varying between 5 and 30 km3 according to different authors (Kittl, 1933; González Ferrán, 1993; Hildreth and Drake, 1992; Ruprecht and Bachmann, 2010), producing a dramatic impact in society, agriculture and local economies in the downwind neighboring affected regions (Abraham and Prieto, 1993; González Ferrán, 1993). The tephra deposits were very uniform in thickness with a notable decreasing grain-size tendency with distance from the source volcano, ranging from 6 cm in neighboring areas and reaching silt and clay sizes around 100 km east (Kittl, 1933; Hildreth and Drake, 1992). The horizon of tephras was recognized as a regional level in a number of natural outcrops pits and excavations, as well as in sediment cores recovered from short drillings (Fig. 3). The tephra level was affected by compaction and post-depositional transformations after 80 years of burying and exposure to weathering and pedogenetic processes, although most of the original characteristics are very well preserved. The sedimentary sequence in which the tephra level is included was recognized regionally by surface and subsurface surveys based on geoelectrical methods and short drillings (Violante et al., 2010; Osella et al., 2010, 2011; de la Vega et al., 2012). The sequence is composed of light brown sandy-silty sediments of lacustrine and eolian origin with high volcaniclastic content and interbedding of buried soils and evaporites (Rovere et al., 2010a,b; D´Ambrosio et al., 2011).



Resumen: El Volcán Quizapú es parte del Complejo Volcánico Cerro Azul-Descabezado Grande, ubicado en la Provincia de Talca, Chile (36,67°S - 70,77°O, altura máxima: 3788 m s.n.m.). La erupción del 10 de abril de 1932 fue uno de los mayores eventos volcánicos del siglo XX. Tuvo un carácter pliniano y arrojó un volumen de tefras entre 5 y 30 km3 (según diferentes autores), que por efecto de los vientos dominantes del oeste cubrieron gran parte de la región central de Argentina, llegando a la costa atlántica y afectando a otros países del este de Sudamérica. Los efectos climáticos y el impacto en las regiones más proximales del sur de Mendoza, particularmente en el Departamento de Malargüe, fueron muy significativos. El estudio de los eyectos constituye un campo de exploración de gran valor no solamente para conocer las características, alcances y efectos de esa erupción sino también para evaluar aspectos relacionados con la tefrología. En esta contribución se analiza un depósito de tefras en los alrededores de la Laguna Llancanelo, en las cercanías de Malargüe, una de las áreas más afectadas por la erupción. Las determinaciones sedimentológicas, mineralógicas y texturales (petrografía, microscopía electrónica y determinaciones químicas semicuantitativas con EDS) permitieron caracterizar la composición granulométrica, petrográfica y química semicuantitativa de las tefras. Estas características son afines a las de los materiales piroclásticos eyectados por la erupción del volcán Quizapú de 1932 estudiados por otros autores, por lo que se asignan a dicho evento volcánico. Las tefras depositadas en la zona de estudio son de tamaño arena muy fina a mediana con significativa cantidad de fracciones menores a 10 µm. Las trizas son pumíceas, fibrosas, con diferentes conformaciones morfológicas y abundante vesicularidad que favorece el entrampamiento de partículas menores en las vesículas de las mayores. La composición química revela un alto contenido de sílice que alcanza hasta cerca del 70% de los componentes, con alrededor de un 15% de Al y cantidades subordinadas de K, Na, Ca, Zn, Mg, Cu, Fe y Ti. Es notorio el alto contenido de K, asociado a un aumento relativo por desilicación de la tefra con el transcurso del tiempo. También son importantes los contenidos de Fe y Cu, en este último caso posiblemente asociado a transformaciones post-depositacionales por meteorización.

The metropolitan area of Napoli (∼3 M inhabitants) in southern Italy is located in between two explosive active volcanoes: Somma-Vesuvius and Campi Flegrei. Pyroclastic density currents (PDCs) from these volcanoes may reach the city center, as witnessed by the Late Quaternary stratigraphic record. Here we compute a novel multivolcano Probabilistic Volcanic Hazard Assessment of PDCs, in the next 50 years, by combining the probability of PDC invasion from each volcano (assuming that they erupt independently) over the city of Napoli and its surroundings. We model PDC invasion with the energy cone model accounting for flows of very different (but realistic) mobility and use the Bayesian Event Tree for Volcanic Hazard to incorporate other volcano-specific information such as the probability of eruption or the spatial variability in vent opening probability. Worthy of note, the method provides a complete description of Probabilistic Volcanic Hazard Assessment, that is, it yields percentile maps displaying the epistemic uncertainty associated with our best (aleatory) hazard estimation. Since the probability density functions of the model parameters of the energy cone are unknown, we propose an ensemble of different hazard assessments based on different assumptions on such probability density functions. The ensemble merges two plausible distributions for the collapse height, reflecting a source of epistemic (specifically, parametric) uncertainty. We also apply a novel quantification for a spatially varying epistemic uncertainty associated to PDC simulations.

A recently excavated locality in the Chemnitz Petrified Forest, lower Permian in age and occurring within the Leukersdorf Formation of the Chemnitz Basin, Germany, provides evidence for an outstanding fossil assemblage buried in situ by pyroclastics. The environment is interpreted as forested lowland that sheltered a dense hygrophilous vegetation of ferns, sphenophytes, and gymnosperms, as well as a diverse fauna of reptiles, amphibians, arthropods, and gastropods. A detailed measured section of the outcrop documents the early volcanic history of the Chemnitz fossil forest, including a paleosol that shows the root systems of Psaronius tree ferns, Arthropitys calamitaleans, and Medullosa and Cordaixylon gymnosperms in the same horizon. Fifty-three trunks are still standing upright and rooted at their place of growth, providing evidence that the top of the paleosol was the land surface on which the forest grew, thereby offering insights into the original plant community structure and density. Taphonomic analysis of both the petrified and adpression-fossil assemblages enable us to reconstruct the direction, estimate the violence and extent of the volcanic events, and their effects on the entire ecosystem. A complete dataset of three-dimensional coordinates resulting from three and one-half years of continuing excavation and study permits the recognition of organ connections and results in the first reconstructions of the excavation site, the floral elements, and the plant community as a whole.

A short trail through the tropical rainforest located between Les Trois Ilets and le Diamant in Martinique, a french Island of the lesser Antilles.
Several magmatic rocks formed during the process of magma mixing can be observed:
pumice stone with garnet, basaltic andesite with garnet.
Rillenkarens on andesite at the end of the trail.

This article identifies the Pucarilla–Cerro Tipillas Volcanic Complex and its major eruptive source, the Luingo caldera (26° 10′S–66° 40′W). Detailed geological mapping, stratigraphic sections, facies analysis and correlations, including the identification of typical caldera components, allow us to infer the position of a collapse caldera, elongated at N65° and with a diameter of 19 km × 13 km, which is responsible for an eruption of 135 km3 (DRE) of magma. The high-crystal contents of the associated ignimbrites, combined with its tectonic setting, indicate that regional and local tectonic structures played a crucial role in the formation of the caldera.The Luingo caldera is located on the south-eastern border of the Puna, and is the south-easternmost recognised caldera of the Altiplano–Puna plateau. The age of the caldera and its products is 12.1 to 13.5 Ma. Based on its location near the Cerro Galán Complex (2 to 6.5 Ma), we can imply that volcanism existed in the area for about 10 Ma. The caldera morphology and product distribution account for a middle Miocene paleao-topography similar to the present one.

Current volcanic reconstructions based on ice core analysis have significantly improved over the past few decades by incorporating multiple-core analyses with a high temporal resolution from different parts of the polar regions into a composite common volcanic eruption record. Regional patterns of volcanic deposition are based on composite records, built from cores taken at both poles. However, in many cases only a single record at a given site is used for these reconstructions. This assumes that transport and regional meteorological patterns are the only source of the dispersion of the volcanic products. Here we evaluate the local-scale variability of a sulfate profile in a low-accumulation site (Dome C, Antarctica), in order to assess the representativeness of one core for such a reconstruction. We evaluate the variability with depth, statistical occurrence, and sulfate flux deposition variability of volcanic eruptions detected in five ice cores, drilled 1 m apart from each other. Local-scale variability, essentially attributed to snow drift and surface roughness at Dome C, can lead to a non-exhaustive record of volcanic events when a single core is used as the site reference, with a bulk probability of 30 % of missing volcanic events and close to 65 % uncertainty on one volcanic flux measurement (based on the standard deviation obtained from a five-core comparison). Averaging n records reduces the uncertainty of the deposited flux mean significantly (by a factor 1∕ √ n); in the case of five cores, the uncertainty of the mean flux can therefore be reduced to 29 %.

The duration and timing of volcanic activity on Mercury are key indicators of the thermal evolution of the planet and provide a valuable comparative example for other terrestrial bodies. The majority of effusive volcanism on Mercury appears to have occurred early in the planet's geological history (~4.1–3.55 Ga), but there is also evidence for explosive volcanism. Here we present evidence that explosive volcanism occurred from at least 3.9 Ga until less than a billion years ago and so was substantially more long-lived than large-scale lava plains formation. This indicates that thermal conditions within Mercury have allowed partial melting of silicates through the majority of its geological history and that the overall duration of volcanism on Mercury is similar to that of the Moon despite the different physical structure, geological history, and composition of the two bodies.

Zusammenfassung Die Exkursion führt nach Chemnitz im Nordosten des Chemnitz-Beckens (Ostdeutschland) und thematisiert die fazielle Entwicklung der unterpermischen Schichtenfolge, ihre Genese und Fossilführung sowie die im Zusammenhang mit der vulkanisch beeinflussten Fossilisation auftretenden taphonomischen Beson-derheiten. Abstract The field-trip visits Chemnitz in the northeastern Chemnitz Basin (E Germany) and illustrates the geological development, formation and fossil content of the early Permian sedimentary and volcanic strata. Specific taphonomic characteristics related to volcanic fossilisation processes are discussed in detail.

Vents and deposits attributed to explosive volcanism occur within numerous impact craters on both the Moon and Mercury. Given the similarities between the two bodies it is probable that similar processes control this spatial association on both. However, the precise morphology and localization of the activity differs on the two bodies, indicating that the nature of structures beneath impact craters and/or volcanic activity may also be different. To explore this, we analyze sites of explosive volcanism within complex impact craters on the Moon and Mercury, comparing the scale and localization of volcanic activity and evidence for post-formation modification of the host crater. We show that the scale of vents and deposits is consistently greater on Mercury than on the Moon, indicating greater eruption energy, powered by a higher concentration of volatiles. Additionally, while the floors of lunar craters hosting explosive volcanism are commonly fractured, those on Mercury are not. The most probable explanation for these differences is that the state of regional compression acting on Mercury's crust through most of the planet's history results in deeper magma storage beneath craters on Mercury than on the Moon. The probable role of the regional stress regime in dictating the depth of intrusion on Mercury suggests that it may also play a role in the depth of sub-crater intrusion on the Moon and on other planetary bodies. Examples on the Moon (and also on Mars) commonly occur at locations where flexural extension may facilitate shallower intrusion than would be driven by the buoyancy of the magma alone.

Eruption source parameters (ESP) characterizing volcanic eruption plumes are crucial inputs for atmospheric tephra dispersal models, used for hazard assessment and risk mitigation. We present FPLUME-1.0, a steady-state 1-D (one-dimensional) cross-section-averaged eruption column model based on the buoyant plume theory (BPT). The model accounts for plume bending by wind, entrainment of ambient moisture, effects of water phase changes, particle fallout and re-entrainment, a new parameterization for the air entrain- ment coefficients and a model for wet aggregation of ash par- ticles in the presence of liquid water or ice. In the occurrence of wet aggregation, the model predicts an effective grain size distribution depleted in fines with respect to that erupted at the vent. Given a wind profile, the model can be used to deter- mine the column height from the eruption mass flow rate or vice versa. The ultimate goal is to improve ash cloud disper- sal forecasts by better constraining the ESP (column height, eruption rate and vertical distribution of mass) and the effec- tive particle grain size distribution resulting from eventual wet aggregation within the plume. As test cases we apply the model to the eruptive phase-B of the 4 April 1982 El Chichón volcano eruption (México) and the 6 May 2010 Eyjafjalla- jökull eruption phase (Iceland). The modular structure of the code facilitates the implementation in the future code ver- sions of more quantitative ash aggregation parameterization as further observations and experiment data will be available for better constraining ash aggregation processes.

The identification of widespread pyroclastic vents and deposits on Mercury has important implications for the planet's bulk volatile content and thermal evolution. However, the significance of pyroclastic volcanism for Mercury depends on the mechanisms by which the eruptions occurred. Using images acquired by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft, we have identified 150 sites where endogenic pits are surrounded by a relatively bright and red diffuse-edged spectral anomaly, a configuration previously used to identify sites of explosive volcanism. We find that these sites cluster at the margins of impact basins and along regional tectonic structural trends. Locally, pits and deposits are usually associated with zones of weakness within impact craters and/or with the surface expressions of individual thrust faults. Additionally, we use images and stereo-derived topographic data to show that pyroclastic deposits are dispersed up to 130 km from their source vent and commonly have either no relief or low circumpit relief within a wider, thinner deposit. These eruptions were therefore likely driven by a relatively high concentration of volatiles, consistent with volatile concentration in a shallow magma chamber prior to eruption. The colocation of sites of explosive volcanism with near-surface faults and crater-related fractures is likely a result of such structures acting as conduits for volatile and/or magma release from shallow reservoirs, with volatile overpressure in these reservoirs a key trigger for eruption in at least some cases. Our findings suggest that widespread, long-lived explosive volcanism on Mercury has been facilitated by the interplay between impact cratering, tectonic structures, and magmatic fractionation.

This study is a reliable proxy linking major impact events could have triggered Large Igneous Provinces (LIP) volcanism and flood basalt eruption at antipodal regions around the globe and also at site of impact. The shockwave created travelled through earth’s interior and triggered a zone of active convection in deep mantle generating huge mantle plumes, possibly leading to widespread increased volcanic activity on Earth’s surface above the plume.
However, not all impacts are reason of flood basalt eruptions but due to change in earth’s upper asthenosphere led by impact could have triggered plume formation. Generation of mantle plume cycle causing creation of Large Igneous Provinces (LIP) Serbian traps, Deccan traps, and also Hawaiian plume hotspot can be traced back to have been caused by major impacts events by asteroids. Modern day proposed hotspots across globe however lie mostly in plate boundaries but some like Hawaiian hotspot can be linked to have been formed due to impact event. With each major impact event theorized and recorded, there is a significant relation of formation of Large Igneous Provinces along antipodal regions of the earth. However, there is still no direct cause that impact must trigger plume formation, but since these impact events were catastrophic and caused major changes in earth’s interior it created Large Igneous Provinces (LIP).
Why antipodal regions? The Chicxulub impactor had an estimated diameter



of 11–81 kilometers (6.8–50.3 mi), and delivered an estimated energy of 21–921 billion Hiroshima A-bombs (between 1.3×1024 and 5.8×1025 joules, or 1.3– 58 yottajoules). This whole energy had to travel through all earth’s interior. Although it is theorized a Mw 9-11 earthquake occurred, the seismic waves could have caused abrupt change in the seismic waves distribution in the transition zones between the Mohorovičić discontinuities and Gutenberg discontinuities. Thus, super-heated material forms (nucleates) at the core-mantle boundary and rises driven by heat exchange across the core-mantle boundary carrying heat upward in a narrow, rising column, and postulated to be independent of plate motions generating deep mantle plumes.
1. Formation of Deccan Traps: Result of linked eruption to the contemporaneous asteroid impact that created the nearly antipodal Chicxulub crater in the Mexican state of Yucatán.
2. Formation of Siberian Traps: Result of linked eruption to Wilkes Land crater in Antarctica, which is estimated to have occurred around the same time and been nearly antipodal to the traps.
3. Formation of Hawaiian Hotspot: Result of two major and largest verified impact craters on Earth. The Vredefort crater and Morokweng impact structure in South Africa, being directly antipodal to Hawaiian Islands.
4. The Azores hotspot: Linked to have been caused by Acraman crater, deeply eroded impact crater in the Gawler Ranges of South Australia antipodal to Azores islands.
Conclusion: There is a significant relation observed in major impact events leading to formation of plume hotspots across the earth and also on the site of impact. The major impact events show the relation in causing abrupt changes in the crustal activity and at antipodal regions too.

Comparison of archaeomagnetic directions in volcani ashes on Santorini and Minoan Late Minon destruction sites on Cretesupport Biblical and Greek decriptions of the end of Atlantis.  The differences between Eastern & Central Cretan sites support an earthquake explanation for their destruction

Sacrofano eruptive center, in the eastern part of the Sabatini volcanic complex, was active between 0.5 and 0.09 m.y. ago. The Baccano geothermal area lies at the western edge of Sacrofano caldera. Sedimentary substrata that form the reservoir for this geothermal system were exposed at the surface at the beginning of volcanic activity. The volcanic history of the Sacrofano center can be divided into three stages: (I) Construction of the Sacrofano pyroclastic edifice by predominantly Strombolian activity. (2) Collapse of Sacrofano caldera following eruption of pyroclastic flows. (3) Development of the Baccano explosive center at the western edge of Sacrofano caldera and collapse of Baccano caldera. Hydrovolcanic activity that began at the end of the first stage of Sacrofano can be explained by a drop in the magma level in the conduit that relieved hydrostatic pressure in the aquifer. As intense fracturing associated with caldera collapse penetrated the carbonate reservoir, the entrapped water flowed towards the conduit to balance the pressure change. The close link between tectonism and volcanism in the Sacrofano center suggests that eruptions there may have been triggered by gravity faults related to regional tectonics.

We analyse a seemingly-unique landform on Mercury: a conical structure, encircled by a trough, and surrounded by a 23,000 km 2 relatively bright and red anomaly of a type interpreted elsewhere on the planet as a pyroclastic deposit. At first glance, this could be interpreted as a volcanically-constructed cone, but if so, it would be the only example of such a landform on Mercury. We make and test the alternative hypothesis that the cone is the intrinsic central peak of an impact crater, the rim crest of which is visible beyond the cone-encircling trough, and that the trough is a vent formed through explosive volcanism that also produced the surrounding bright, red spectral anomaly. We test this hypothesis by comparing the morphology of the cone and the associated landform assemblage with morphologically-fresh impact craters of the same diameter as the putative host crater, and additionally, by modelling the original morphology of such a crater using a hydrocode model. We show that the present topography can be explained by formation of a vent completely encircling the crater's central peak and also make the observation that explosive volcanic vents frequently occur circumferential to the central peaks of impact craters on Mercury. This indicates that, although this cone initially appears unique, it is in fact an unusually well-developed example of a common process by which impact-related faults localize magma ascent near the centre of impact craters on Mercury, and represents an extreme end-member of the resulting landforms.

The present contribution describes and analyses the spatial-temporal distribution and main features of the volcanic rocks, with emphasis in pyroclastic deposits, located in the 25-28°S segment of the Central Andes. We built a new database, based on our own field studies and compilation from the literature, where we discriminate the different pyroclastic units. We find that the pyroclastic deposits cover an area of at least 7770 km 2 and are distributed mainly along N-S to NNE-SSW, NW-SE to WNW-ESE and NE-SW trends. The spatial distribution of these deposits has varied with time: those N 14.5 Ma are concentrated west of 69°W; during 14.5-11.5 Ma explosive magmatism shifted east of 67°W; the deposits b11.5 Ma became more dispersed. The main explosive activity occurred during the 26-18 Ma, 14.5-11.5 Ma and ≤5.3 Ma intervals. For pyroclastic deposits, dacitic compositions dominate during the Miocene, whereas rhyodacitic and rhyolitic compositions are more abundant since the Pliocene. In the 25-28°S segment of the CVZ there is no clear migration pattern of the magmatism, except for the well-known eastward migration occurred at ca. 26 Ma. Moreover, we find that a) basement lithology or composition or mechanical features influenced distribution of volcanic activity; b) the NE-SW alignment of b2.5 Ma caldera complexes coincides with the maximum depth of the Moho discontinuity and may be a further indicator of delamination processes in the Puna-Eastern Cordillera/Pampean Ranges border; and c) intense explosive volcanism concentrated during the 14-11.5 Ma interval along the eastern Puna border, which coincides in time with a peak in deformation and in space with the contact between basement units with different mechanical properties. No relationship between magmatic activity and azimuth or convergence rate between South American and Nazca plates are found, except for a peak in convergence rate at~26 Ma.

Recent explosive volcanic eruptions recorded worldwide (e.g. Hekla in 2000, Eyjafjallajökull in 2010, Cordón-Caulle in 2011) demonstrated the necessity for a better assessment of the eruption source parameters (ESPs; e.g. column height, mass eruption rate, eruption duration, and total grain-size distribution-TGSD) to reduce the uncertainties associated with the far-travelling airborne ash mass. Volcanological studies started to integrate observations to use more realistic numerical inputs, crucial for taking robust volcanic risk mitigation actions. On 23 November 2013, Etna (Italy) erupted, producing a 10 km height plume, from which two volcanic clouds were observed at different altitudes from satellites (SEVIRI, MODIS). One was retrieved as mainly composed of very fine ash (i.e. PM 20), and the second one as made of ice/SO 2 droplets (i.e. not measurable in terms of ash mass). An atypical north-easterly wind direction transported the tephra from Etna towards the Calabria and Apulia regions (southern Italy), permitting tephra sampling in proximal (i.e. ∼ 5-25 km from the source) and medial areas (i.e. the Calabria region, ∼ 160 km). A primary TGSD was derived from the field measurement analysis, but the paucity of data (especially related to the fine ash fraction) prevented it from being entirely representative of the initial magma fragmentation. To better constrain the TGSD assessment, we also estimated the distribution from the X-band weather radar data. We integrated the field and radar-derived TGSDs by inverting the relative weighting averages to best fit the tephra loading measurements. The resulting TGSD is used as input for the FALL3D tephra dispersal model to reconstruct the whole tephra loading. Furthermore, we empirically modified the integrated TGSD by enriching the PM 20 classes until the numerical results were able to reproduce the airborne ash mass retrieved from satellite data. The resulting TGSD is inverted by best-fitting the field, ground-based, and satellite-based measurements. The results indicate a total erupted mass of 1.2 × 10 9 kg, being similar to the fieldderived value of 1.3 × 10 9 kg, and an initial PM 20 fraction between 3.6 and 9.0 wt %, constituting the tail of the TGSD. 1 Introduction Volcanic explosive eruptions pose hazards related to the release of large quantities of material into the atmosphere. The observation of the eruption features, such as the eruptive column, the tephra loading, or the far-travelling volcanic plume, aims at characterizing the eruption source parameters (ESPs). Hazard assessment related to tephra dispersal, and its implications for aviation safety and public health, is one of the Published by Copernicus Publications on behalf of the European Geosciences Union.

Archaeomagnetic dating on the Minoan ash horizons of the Santorini volcano and on fired destruction levels at late Minoan sites on Crete demonstrates that the basal (Plinian) air-fall ash of the first'Minoan'pumice is contemporaneous with the destruction levels on central ...

The Ilopango caldera is the source of the large Tierra Blanca Joven (TBJ) eruption that occurred about 1.5 ka years ago, between ca. AD270 and AD535. The eruption dispersed volcanic ash over much of the present territory of El Salvador, and pyroclastic density currents (PDCs) extended 40 km from the volcano. In this study, we document the physical characteristics of the deposits from all over El Salvador to further constrain the eruption processes and the intensity and magnitude of the different phases of the eruption. The succession of deposits generated by the TBJ eruption is made of 8 units. The eruption started with PDCs of hydromagmatic origin (Unit A 0), followed by fallout deposits (Units A and B) that are b15 cm thick and exposed in sections close to the Ilopango caldera (within 10-15 km). The eruption, then, transitioned into a regime that generated further PDCs (Units C-F), these range from dilute to dense and they filled the depressions near the Ilopango caldera with thicknesses up to 70 m. Deposits from the co-ignimbrite plume (Unit G) are the most widespread, the deposits are found in Guatemala, Honduras, Nicaragua, Costa Rica and the Pacific Ocean and cm-thick across El Salvador. Modelling of the deposits suggests that column heights were 29 km and 7 km for the first two fallout phases, and that the co-ignimbrite phoenix plume rose up to 49 km. Volumes estimated for the fallout units are 0.15, 0.8 and 16 km 3 dense rock equivalent (DRE) for Unit A, B and G respectively. The PDCs deposits volumes were estimated to be ~0.5, ~3.3, ~0.3 and ~9.1 km 3 DRE for Units C, D, E and F, respectively. The combined volume of TBJ deposits is ~30 km 3 DRE (~58 km 3 bulk rock), indicating that it was one of largest Holocene eruptions from Central America. This eruption occurred while Mayan populations were living in the region and it would have had a significant impact on the areas within tens of kilometres of the vent for many years to decades after the eruption.

The Chemnitz Fossil Forest depicts one of the most completely preserved forest ecosystems in late Paleozoic Northern Hemisphere of tropical Pangaea. Fossil biota was preserved as a T 0 taphocoenosis resulting from the instantaneous entomb-ment by volcanic ashes of the Zeisigwald Tuff. The eruption depicts one of the late magmatic events of post-variscan rhy-olitic volcanism in Central Europe. This study represents a multi-method evaluation of the pyroclastic ejecta encompassing sedimentological and (isotope) geochemical approaches to shed light on magmatic and volcanic processes, and their role in preserving the fossil assemblage. The Zeisigwald Tuff pyroclastics (ZTP) reveal a radiometric age of 291 ± 2 Ma, pointing to a late Sakmarian/early Artinskian (early Permian) stratigraphic position for the Chemnitz Fossil Forest. The initial eruption was of phreatomagmatic style producing deposits of cool, wet ashes, which deposited from pyroclastic fall out and density currents. Culmination of the eruption is reflected by massive hot and dry ignimbrites. Whole-rock geochemistry and zircon grain analysis show that pyroclastic deposits originated from a felsic, highly specialised magma, which underwent advanced fractionation, and is probably related to post-Carboniferous magmatism in the Western Erzgebirge. The ascending magma recycled old cadomic crust of the Saxo-thuringian zone, likely induced by a mantle-derived heat flow during a phase of post-variscan crustal delamination. Geochemical trends within the succession of the basal pyroclastic horizons reflect inverse zonation of the magma chamber and provide evidence for the continuous eruption and thus a simultaneous burial of the diverse ecosystem.

Course name: Earth Systems I: Solid Earth

Saint Louis University, Madrid Campus, Faculty: Science and Engineering

Semester:  Spring 2005.

Course description: On the structure of our planet and the forming processes: plate tectonics, crustal evolution, rocks, surface and groundwater hydrology, and so on. Focus on volcanic activity in the Canary Islands, where students will carry out field studies during a long-weekend visit.
Mandatory trip: Lanzarote (Canary Islands); unpaid fees result in automatic removal from class.

Course Objectives: 
By end of the course the student should:
• Know the basic types of rocks and understand the basic principles of the rock cycle.
• Know and understand the basic principles of plate tectonics and volcanism.
• Know and understand the most important processes on the earth´s surface.
• Achieve a foundation on the basic principles underlying the patterns and dynamics of the earth´s surface and interior.

Textbook: Following textbook is absolutely necessary for the course:
PRESS, Frank, & SIEVER, Raymond (2001): Understanding Earth. 3rd edition. – New York (W. H. Freeman and Company).

Supplementary reading: Following books may be interesting or helpful for some aspects of the course, but they are not necessary:
ANDEL, T. H. van, (1994): New views on an old planet. A history of global change. 439 pp.; Cambridge (Cambridge University Press).
ARAÑA, V., & CARRACEDO, J. C. (1979): Los volcanes de las islas Canarias. – Vol. I: Tenerife; Vol. II: Lanzarote y Fuerteventura.
BOLT, Bruce A. (1999): Earthquakes. – 366 p.; New York (W. H. Freeman and Company).
CUNNINGHAM, W.P., & SAIGO, B. Woodworth (1992): Environmental Science – A Global Concern. 2nd edition. – 622 p., Dubuque (Wm. C. Brown Publishers).
CUNNINGHAM, W.P., & CUNNINGHAM, M.A., & SAIGO, B. Woodworth (2002): Environmental Science – A Global Concern. 7th edition. – 646 p., Boston.
DECKER, Robrt & Barbara: Volcanoes. – 321 p.; New York (W. H. Freeman and Company).
MERRITTS, D., & WET, A. DE, & MENKING, K. (1998): Environmental geology. 452 pp.; New York (Freeman a. Co.).
SCARTH, Alwyn & TANGUY, Jean-Claude (2000): Volcanoes of Europe. – Oxford.
YARZA, Esperanza (1988): Volcanes de Iberoamerica. – 128 p.; Madrid (Anaya).

Course Calendar:
Tuesday, Jan. 18th: Introduction – Building a planet (Textbook chapter 1)
Thursday, Jan. 20th: Minerals (Textbook chapter 2)
Tuesday, Jan. 25 & Thursday, Jan. 27: Rocks (Textbook chapter 3)
Thursday, Jan. 27: End of DROP/ADD period
Tuesday, Feb. 1 & Thursday, Feb. 3: Igneous Rocks (Textbook chapter 4)
Tuesday, Feb. 8 & Thursday, Feb. 10: Volcanism (I) (Textbook chapter 5)
Tuesday, Feb. 15: Review & Preparation of first mid-term exam
Tuesday, Feb. 15: Deadline for the submission of the title of the paper
Thursday, Feb. 17: First mid-term exam
Tuesday, Feb. 22 & Thursday, Feb. 24: Volcanism (II) (Textbook chapter 5)
Tuesday, Mar. 1 & Thursday, Mar. 3: Volcanism (III) (Textbook chapter 5)
Saturday, Mar. 5, to Sunday, Mar. 13: SPRING BREAK
Tuesday, Mar. 15: Weathering and Erosion (Textbook chapter 6)
Thursday, Mar. 17, to Sunday, Mar.20: Field trip to the Canary Islands
Tuesday, Mar. 22: Sediments and Sedimentary Rocks (I) (Chapter 7)
Thursday, Mar. 24, to Sunday, Mar.27: Easter
Tuesday, Mar. 29: Review & Preparation of second mid-term exam
Thursday, Mar. 31: Second mid-term exam
Tuesday, Apr. 5: Deadline for the submission of papers and PowerPoint presentations
Tuesday, Apr. 5: Sediments and Sedimentary Rocks (II) (Chapter 7)
Thursday, Apr. 7: Metamorphic Rocks (Textbook chapter 8)
Thursday, Apr. 7: Deadline for the submission of the exercise
Friday, Apr. 8: Last day to drop a class and receive a grade of "W"
Tuesday, Apr. 12: The Rock Record and the Geologic Time Scale (Textbook chapter 9)
Thursday, Apr. 14: Rock Deformation (Textbook chapter 10)
Tuesday, Apr. 19 & Thursday, Apr. 21: The Hydrologic Cycle and Groundwater (Chapter 12)