Structural weakening of the Merapi dome identified by drone photogrammetry after the 2010 eruption

Lava domes are subjected to structural weakening that can lead to gravitational collapse and produce pyroclastic flows that may travel up to several kilometers from a volcano's summit. At Merapi volcano, Indonesia, pyroclastic flows are a major hazard, frequently causing high numbers of casualties. After the Volcanic Explosivity Index 4 eruption in 2010, a new lava dome developed on Merapi volcano and was structurally destabilized by six steam-driven explosions between 2012 and 2014. Previous studies revealed that the explosions produced elongated open fissures and a delineated block in the southern dome sector. Here, we investigated the geomorphology, structures, thermal fingerprint, alteration mapping and hazard potential of the Merapi lava dome by using drone-based geomorphologic data and forward-looking thermal infrared images. The block on the southern dome of Merapi is delineated by a horseshoe-shaped structure with a maximum depth of 8&thinsp;m and it is located on the unbuttressed southern steep flank. We identify intense thermal, fumarole and hydrothermal alteration activities along this horseshoe-shaped structure. We conjecture that hydrothermal alteration may weaken the horseshoe-shaped structure, which then may develop into a failure plane that can lead to gravitational collapse. To test this instability hypothesis, we calculated the factor of safety and ran a numerical model of block-and-ash flow using Titan2D. Results of the factor of safety analysis confirm that intense rainfall events may reduce the internal friction and thus gradually destabilize the dome. The titan2D model suggests that a hypothetical gravitational collapse of the delineated unstable dome sector may travel southward for up to 4&thinsp;km. This study highlights the relevance of gradual structural weakening of lava domes, which can influence the development fumaroles and hydrothermal alteration activities of cooling lava domes for years after initial emplacement.</p

Changing eruptive styles and textural features from phreatomagmatic to strombolian activity of basaltic littoral cones: Los Erales cinder cone, Tenerife, Canary Islands

Monta&ntilde;a Los Erales is a 70 m high Quaternary cinder cone in the Bandas del Sur region, south Tenerife. Field observations on excavated sections and SEM analysis of tephra samples from the cone suggest that the eruption style of this vent changed progressively from an initial hydrovolcanic phase, through a transitional stage, to one that was entirely strombolian. Clast sizes increase from &le;1 cm angular lapilli in hydrovolcanic samples to 15 cm bombs in strombolian samples. Vesicles also increase in size from 0.5 mm to 1.2 mm, becoming more rounded in the strombolian samples. Palagonitization, extensive in the hydrovolcanic deposits, becomes less noticeable in strombolian deposits. To investigate the causes for and the nature of these changes in eruptive style, products from each major unit were analysed for their morphology, using scanning electron microscopy with both SE and BSE imaging as tephra morphologies are known to reflect the eruptive regime and degree of explosivity at the time of eruption. SEM imaging of hydrovolcanic samples illustrate angular fragments that have been rapidly quenched and contain high levels of palagonitisation and zeolitisation, whereas strombolian samples appear to be less altered and display larger clast sizes and vesicles. Our results confirm that the initial phase of activity was largely driven by magma-water (coolant) interaction, where magma may have interacted with a lens of fresh ground or surface water, causing intense fragmentation of the magma. With proceeding eruptive activity the water became exhausted, giving rise to an entirely strombolian eruptive style. Additionally, fossil diatoms were found in hydrovolcanic samples, further emphasising the influence of a, probably fluvial, water source during the early phase of emplacement.La Monta&ntilde;a de Los Erales es un cono de c&iacute;nder del Cuaternario de 70 m de altura situado en la zona de las Bandas del Sur, en el litoral meridional de la isla de Tenerife. Observaciones de campo en secciones excavadas en los flancos del cono y an&aacute;lisis SEM de las muestras de tefra sugieren que el estilo eruptivo de este aparato volc&aacute;nico cambi&oacute; progresivamente durante la erupci&oacute;n de una fase inicial hidrovolc&aacute;nica a una final enteramente estromboliana, con estadios intermedios transicionales. El tama&ntilde;o de los clastos aumenta de &le;1 cm de lapilli angular en las muestras hidrovolc&aacute;nicas a bombas de 15 cm en las estrombolianas. Las ves&iacute;culas tambi&eacute;n aumentan en tama&ntilde;o desde 0,5 mm a 1,2 mm, volvi&eacute;ndose m&aacute;s redondeadas en las muestras estrombolianas. Los intensos procesos de palagonitizaci&oacute;n de los dep&oacute;sitos hidrovolc&aacute;nicos son menos significativos en las fases estrombolianas. Con objeto de investigar la naturaleza y las causas de estos cambios se analiz&oacute; la morfolog&iacute;a de los productos de las principales fases. Se han utilizado para ello im&aacute;genes de microscop&iacute;a electr&oacute;nica (SE y BSE), ya que se sabe que las diferentes morfolog&iacute;as de estos piroclastos reflejan el r&eacute;gimen eruptivo y el grado de explosividad durante la erupci&oacute;n. Las im&aacute;genes SEM de las muestras hidrovolc&aacute;nicas presentan fragmentos angulares que se han enfriado r&aacute;pidamente y con elevado grado de palagonitizaci&oacute;n y zeolitizaci&oacute;n. Las estrombolianas, en cambio, aparecen menos alteradas y muestran mayor tama&ntilde;o de clastos y ves&iacute;culas. Los resultados obtenidos indican que la fase inicial de la erupci&oacute;n se caracteriza por una importante interacci&oacute;n magma-agua (refrigerante), probablemente relacionada con una cantidad limitada de agua superficial o fre&aacute;tica que produjo la intensa fragmentaci&oacute;n del magma. En el transcurso de la erupci&oacute;n la fuente de agua se agot&oacute;, dando lugar a las fases finales de car&aacute;cter enteramente estromboliano. F&oacute;siles de diatomeas, que se han encontrado asociados a las muestras hidrovolc&aacute;nicas, refuerzan la posibilidad de que el agua fuera de origen superficial, probablemente el cauce de un barranco

Magma Ascent along a Major Terrane Boundary: Crustal Contamination and Magma Mixing at the Drumadoon Intrusive Complex, Isle of Arran, Scotland

The composite intrusions of Drumadoon and An Cumhann crop out on the SE coast of the Isle of Arran, Scotland and form part of the larger British and Irish Palaeogene Igneous Province, a subset of the North Atlantic Igneous Province. The intrusions (shallow-level dykes and sills) comprise a central quartz-feldspar-phyric rhyolite flanked by xenocryst-bearing basaltic andesite, with an intermediate zone of dark quartz-feldspar-phyric dacite. New geochemical data provide information on the evolution of the component magmas and their relationships with each other, as well as their interaction with the crust through which they travelled. During shallow-crustal emplacement, the end-member magmas mixed. Isotopic evidence shows that both magmas were contaminated by the crust prior to mixing; the basaltic andesite magma preserves some evidence of contamination within the lower crust, whereas the rhyolite mainly records upper-crustal contamination. The Highland Boundary Fault divides Arran into two distinct terranes, the Neoproterozoic to Early Palaeozoic Grampian Terrane to the north and the Palaeozoic Midland Valley Terrane to the south. The Drumadoon Complex lies within the Midland Valley Terrane but its isotopic signatures indicate almost exclusive involvement of Grampian Terrane crust. Therefore, although the magmas originated at depth on the northern side of the Highland Boundary Fault, they have crossed this boundary during their evolution, probably just prior to emplacemen

CO2 bubble generation and migration during magma-carbonate interaction

We conducted quantitative textural analysis of vesicles in high temperature and pressure carbonate assimilation experiments (1200 °C, 0.5 GPa) to investigate CO2 generation and subsequent bubble migration from carbonate into magma. We employed Mt. Merapi (Indonesia) and Mt. Vesuvius (Italy) compositions as magmatic starting materials and present three experimental series using (1) a dry basaltic-andesite, (2) a hydrous basaltic-andesite (2 wt% H2O), and (3) a hydrous shoshonite (2 wt% H2O). The duration of the experiments was varied from 0 to 300 s, and carbonate assimilation produced a CO2-rich fluid and CaO-enriched melts in all cases. The rate of carbonate assimilation, however, changed as a function of melt viscosity, which affected the 2D vesicle number, vesicle volume, and vesicle size distribution within each experiment. Relatively low-viscosity melts (i.e. Vesuvius experiments) facilitated efficient removal of bubbles from the reaction site. This allowed carbonate assimilation to continue unhindered and large volumes of CO2 to beliberated, a scenario thought to fuel sustained CO2-driven eruptions at the surface. Conversely, at higher viscosity (i.e. Merapi experiments), bubble migration became progressively inhibited and bubble concentration at the reaction site caused localised volatile over-pressure that can eventually trigger short-lived explosive outbursts. Melt viscosity therefore exerts a fundamental control on carbonate assimilation rates and, by consequence, the style of CO2-fuelled eruptions

CO2 bubble generation and migration during magma–carbonate interaction

We conducted quantitative textural analysis of vesicles in high temperature and pressure carbonate assimilation experiments (1200&nbsp;°C, 0.5&nbsp;GPa) to investigate CO2 generation and subsequent bubble migration from carbonate into magma. We employed Mt. Merapi (Indonesia) and Mt. Vesuvius (Italy) compositions as magmatic starting materials and present three experimental series using (1) a dry basaltic-andesite, (2) a hydrous basaltic-andesite (2&nbsp;wt% H2O), and (3) a hydrous shoshonite (2&nbsp;wt% H2O). The duration of the experiments was varied from 0 to 300&nbsp;s, and carbonate assimilation produced a CO2-rich fluid and CaO-enriched melts in all cases. The rate of carbonate assimilation, however, changed as a function of melt viscosity, which affected the 2D vesicle number, vesicle volume, and vesicle size distribution within each experiment. Relatively low-viscosity melts (i.e. Vesuvius experiments) facilitated efficient removal of bubbles from the reaction site. This allowed carbonate assimilation to continue unhindered and large volumes of CO2 to be liberated, a scenario thought to fuel sustained CO2-driven eruptions at the surface. Conversely, at higher viscosity (i.e. Merapi experiments), bubble migration became progressively inhibited and bubble concentration at the reaction site caused localised volatile over-pressure that can eventually trigger short-lived explosive outbursts. Melt viscosity therefore exerts a fundamental control on carbonate assimilation rates and, by consequence, the style of CO2-fuelled eruptions

Magma-Carbonate Interaction Processes and Associated CO2 Release at MerapiVolcano, Indonesia: Insights from Experimental Petrology

There is considerable evidence for continuing, late-stage interaction between the magmatic system at Merapi volcano, Indonesia, and local crustal carbonate (limestone). Calc-silicate xenoliths within Merapi basaltic-andesite eruptive rocks display textures indicative of intense interaction between magma and crustal carbonate, and Merapi feldspar phenocrysts frequently contain crustally contaminated cores and zones. To resolve the interaction processes between magma and limestone in detail we have performed a series of time-variable decarbonation experiments in silicate melt, at magmatic pressure and temperature, using a Merapi basaltic-andesite and local Javanese limestone as starting materials.We have used in situ analytical methods to determine the elemental and strontium isotope composition of the experimental products and to trace the textural, chemical, and isotopic evolution of carbonate assimilation. The major processes of magma^carbonate interaction identified are: (1) rapid decomposition and degassing of carbonate; (2) generation of a Ca-enriched, highly radiogenic strontium contaminant melt, distinct from the starting material composition; (3) intense CO2 vesiculation, particularly within the contaminated zones; (4) physical mingling between the contaminated and unaffected melt domains; (5) chemical mixing between melts. The experiments reproduce many of the features of magma^carbonate interaction observed in the natural Merapi xenoliths and feldspar phenocrysts. The Ca-rich, high 87Sr/86Sr contaminant melt produced in the experiments is considered as a precursor to the Ca-rich (often ‘hyper-calcic’) phases found in the xenoliths and the contaminated zones inMerapi feldspars.The xenoliths also exhibit micro-vesicular textures that can be linked to the CO2 liberation process seen in the experiments.This study, therefore, provides well-constrained petrological insights into the problem of crustal interaction at Merapi and points toward the substantial impact of such interaction on the volatile budget of the volcano

La erupción submarina de La Restinga en la isla de El Hierro, Canarias: Octubre 2011-Marzo 2012

The first signs of renewed volcanic activity at El Hierro began in July 2011 with the occurrence of abundant, low-magnitude earthquakes. The increasing seismicity culminated on October 10, 2011, with the onset of a submarine eruption about 2 km offshore from La Restinga, the southernmost village on El Hierro. The analysis of seismic and deformation records prior to, and throughout, the eruption allowed the reconstruction of its main phases: 1) ascent of magma and migration of hypocentres from beneath the northern coast (El Golfo) towards the south rift zone, close to La Restinga, probably marking the hydraulic fracturing and the opening of the eruptive conduit; and 2) onset and development of a volcanic eruption indicated by sustained and prolonged harmonic tremor whose intensity varied with time. The features monitored during the eruption include location, depth and morphological evolution of the eruptive source and emission of floating volcanic bombs. These bombs initially showed white, vesiculated cores (originated by partial melting of underlying pre-volcanic sediments upon which the island of El Hierro was constructed) and black basanite rims, and later exclusively hollow basanitic lava balloons. The eruptive products have been matched with a fissural submarine eruption without ever having attained surtseyan explosiveness. The eruption has been active for about five months and ended in March 2012, thus becoming the second longest reported historical eruption in the Canary Islands after the Timanfaya eruption in Lanzarote (1730-1736). This eruption provided the first opportunity in 40 years to manage a volcanic crisis in the Canary Islands and to assess the interpretations and decisions taken, thereby gaining experience for improved management of future volcanic activity. Seismicity and deformation during the eruption were recorded and analysed by the Instituto Geográfico Nacional (IGN). Unfortunately, a lack of systematic sampling of erupted pyroclasts and lavas, as well as the sporadic monitoring of the depth and growth of the submarine vent by deployment of a research vessel, hampered a comprehensive assessment of hazards posed during volcanic activity. Thus, available scientific data and advice were not as high quality as they could have been, thereby limiting the authorities in making the proper decisions at crucial points during the crisis. The response in 2011-12 to the El Hierro eruption has demonstrated that adequate infrastructure and technical means exist in the Canary Islands for the early detection of potential eruptive hazards. However, it also has taught us that having detailed emergency management plans may be of limited value without an accompanying continuous, well-integrated scientific monitoring effort (open to national and international collaboration) during all stages of an eruption.Los primeros indicios de una posible erupción volcánica en El Hierro se percibieron a partir de julio de 2011 en forma de sismos de baja intensidad pero anormalmente numerosos. La intensificación de la sismicidad culminó con el inicio de la erupción submarina el 10 de octubre de 2011 a unos 2 km al sur de La Restinga. La sismicidad y deformación del terreno que precedieron y acompañaron a esta erupción han permitido reconstruir las principales fases de actividad volcánica: 1) generación y ascenso del magma con migración de los hipocentros sísmicos desde el norte, en el Golfo, hasta el rift sur, en La Restinga, marcando la apertura hidráulica del conducto magmático; y 2) inicio y continuidad de la erupción volcánica evidenciada por un tremor armónico continuo de intensidad variable en el tiempo. Las características observadas a lo largo de la erupción, principalmente localización, profundidad y evolución morfológica del foco emisor, así como emisión de materiales volcánicos flotantes, inicialmente con un núcleo blanco poroso (procedentes de la fusión parcial de sedimentos de la capa superior de la corteza oceánica anteriores a la construcción del edificio insular de El Hierro) envuelto por una corteza basanítica y después huecas (lava balloons), se han correspondido con una erupción submarina fisural profunda sin que nunca hayan intervenido mecanismos más explosivos tipo surtseyano. La erupción se mantuvo activa durante unos cinco meses, dándose por finalizada en marzo del 2012, convirtiéndose de este modo en la segunda erupción histórica más longeva de Canarias después de la de Timanfaya (1730-36) en Lanzarote. Esta erupción ha supuesto la primera oportunidad en 40 años de gestionar una crisis volcánica en Canarias y de analizar las observaciones e interpretaciones y las decisiones adoptadas, con objeto de mejorar la gestión de futuras crisis volcánicas. El Instituto Geográfico Nacional (IGN) se encargó de adquirir y analizar la información sísmica y de deformación durante todo el proceso. Sin embargo, no se dispuso inicialmente de un barco oceanográfico que realizara estudios sistemáticos de la profundidad y progresión de la erupción, así como de toma de muestras de los materiales emitidos (piroclastos y lavas), elementos claves para la determinación de la peligrosidad eruptiva. Estas deficiencias en el seguimiento científico del proceso eruptivo dificultaron en algunos momentos la toma de decisiones de protección civil. El análisis de la crisis ha puesto de manifiesto que, aunque se disponga de una infraestructura técnica adecuada para la detección temprana de crisis eruptivas en el archipiélago, de poco valen las medidas administrativas planificadas sin un seguimiento científico continuo e integrador del proceso eruptivo, abierto a la colaboración científica nacional e internacional

Investigating H2O contents in clinopyroxene from explosive versus effusive eruption products from Merapi volcano, Indonesia

&amp;lt;p&amp;gt;The 2010 eruption of Merapi produced pyroclastic deposits and lava flows that are compositionally very similar, raising the question as to the underlying reason of the differences in eruptive styles between the various phases of the 2010 eruptive events. To test whether primary magmatic volatile content is the reason for the different eruption styles, we analyzed magmatic water contents in nominally anhydrous clinopyroxene crystals contained in lava and ash from the 2010 eruptive events. We utilized two analytical approaches: (i) Fourier-transform infrared spectroscopy (FTIR) analysis of fresh clinopyroxene from the ash and lava samples and (ii) FTIR analysis of clinopyroxene both prior to and after experimental re-hydration. By employing calculated partition coefficients, we determined the magmatic water content of the magma from which the various crystals grew. The magmatic water content determined from the unmodified clinopyroxenes from lava samples yield a range of 0.35 wt.% to 2.02 wt.% H&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O, whereas magmatic water contents determined from untreated clinopyroxene contained in the ash samples range between 0.04 and 3.25 wt.%, with two outliers at 4.62 and 5.19 and wt.%, respectively. In contrast, for the rehydrated crystals the range for lava derived clinopyroxene crystals is between 1.94 and 2.19 wt.% and for ash between 1.74 and 2.66 wt.%, with two crystals at extreme values of 0.85 and 3.20 wt.%. We interpret these results to indicate that crystals from different populations are present in the 2010 eruptive products, with the dominant group reflecting relatively low magmatic H&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O contents (around 2 wt.%) due to storage in shallow magma reservoirs and pockets at high levels within the Merapi plumbing systems (e.g. top 3 km). The overall higher H&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O range and the occasionally more extreme values recorded in clinopyroxenes from ash deposits may then represent the presence of a crystal population that last equilibrated at deeper levels and at higher water contents, i.e. these crystals derive from the replenishing magma that activated the shallow portion of the plumbing system during the 2010 events. While this is work in progress, our results so far seem to suggest that the pyroclastic deposits of the 2010 Merapi eruption may contain a higher fraction of clinopyroxene derived from &amp;amp;#8216;deeper magma&amp;amp;#8217; with higher H&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O contents then what we have detected in associated lavas.&amp;lt;/p&amp;gt; </jats:p

Landscape science: a Russian geographical tradition

The Russian geographical tradition of landscape science (landshaftovedenie) is analyzed with particular reference to its initiator, Lev Semenovich Berg (1876-1950). The differences between prevailing Russian and Western concepts of landscape in geography are discussed, and their common origins in German geographical thought in the late nineteenth and early twentieth centuries are delineated. It is argued that the principal differences are accounted for by a number of factors, of which Russia's own distinctive tradition in environmental science deriving from the work of V. V. Dokuchaev (1846-1903), the activities of certain key individuals (such as Berg and C. O. Sauer), and the very different social and political circumstances in different parts of the world appear to be the most significant. At the same time it is noted that neither in Russia nor in the West have geographers succeeded in specifying an agreed and unproblematic understanding of landscape, or more broadly in promoting a common geographical conception of human-environment relationships. In light of such uncertainties, the latter part of the article argues for closer international links between the variant landscape traditions in geography as an important contribution to the quest for sustainability