Volcanica 2019-05-11T21:34:02+00:00 Jamie Farquharson Open Journal Systems <p><em>Volcanica</em>&nbsp;publishes high-quality, rigorously peer reviewed research pertaining to volcanology and related disciplines, while eliminating submission fees and keeping content freely accessible.</p> DensityX: A program for calculating the densities of magmatic liquids up to 1,627 °C and 30 kbar 2019-04-19T12:33:32+00:00 Kayla Iacovino Christy B Till <p>Here we present a standalone program, DensityX, to calculate the densities of hydrous silicate melts (1,000s of samples in a single model run) given pressures, temperatures, and major oxide compositions in wt% in the 10-component system SiO<sub>2</sub>-TiO<sub>2</sub>-Al<sub>2</sub>O<sub>3</sub>-Fe<sub>2</sub>O<sub>3</sub>-FeO-MgO-CaO-Na<sub>2</sub>O-K<sub>2</sub>O-H<sub>2</sub>O. Here we use DensityX to analyze over 3,000 melt inclusions over a wide compositional range to visualize the distribution of natural silicate liquid densities in the Earth’s crust. The program is open-source, written in Python, and can be accessed and run via an online interface through a web browser at <a href=""></a> or by downloading and running the code from a github repository. A companion Excel spreadsheet can also be used to run density calculations identical to those in the Python script but only for one sample at a time. In another example application, we demonstrate how DensityX can be used to constrain density-driven convective cycling in the phonolitic lava lake of Erebus volcano, Antarctica.</p> 2019-02-11T18:36:45+00:00 ##submission.copyrightStatement## Evaluating emplacement temperature of a 1000-year sequence of mass flows using paleomagnetism of their deposits at Mt. Taranaki, New Zealand 2019-04-19T12:33:32+00:00 Geoffrey A Lerner Shane J Cronin Gillian M Turner <p>Temperature can be an important characteristic used to distinguish primary pyroclastic density currents or block-and-ash flows from other collapses not primarily related to an eruption, and also governs the type and level of hazard presented by these mass flows. We examined several mass-flow deposits within the AD1000-1800 Maero Formation at Mt. Taranaki, New Zealand, for field characteristics of hot emplacement - such as the presence of charcoal, baking of soils, or gas-elutriation piping - and conducted a paleomagnetic study of their thermoremanent magnetization (TRM) to determine emplacement temperatures. Results show that the majority of the deposits result from block-and-ash flows emplaced over ~500°C. Some of these deposits were indistinguishable in the field from a re-worked or low-temperature emplaced lahar or landslide deposit, indicating that sedimentary features are not a clear determinant of high emplacement temperature. The high emplacement temperatures suggest that the time between dome emplacement and collapse during this period was usually brief (&lt;30 years), with some events consisting of rapid and repeated growth and collapse of lava domes, possibly within the same prolonged lava effusion episode.</p> 2019-04-06T12:42:54+00:00 ##submission.copyrightStatement## Structures controlling volcanic activity within Masaya caldera, Nicaragua 2019-05-06T14:18:13+00:00 Guillermo Caravantes González Hazel Rymer Jeffrey Zurek Susanna Ebmeier Stephen Blake Glyn Williams-Jones <p>Geophysical and geological observations collected in 2007-2012 shed light on the mechanisms controlling the style and location of eruptions within the Las Sierras-Masaya Caldera complex, Nicaragua. These results confirm a hypothesised ~3.5 km diameter structure with features compatible with the presence of a ring fracture (50-65°, with inward-dipping bounding walls). A central block is bound by this fracture and defines an incipient nested caldera related to the emptying of the magma chamber following the last Plinian eruption (1.8 ka). The prolongation of the Cofradías fault from the Managua graben represents the most significant structure on the floor of Masaya caldera. Current activity, including a convecting lava lake, largely depends on the interplay between the extensional stress regime associated with the Managua graben and deformation along the inner caldera bounding fault. This high spatial resolution survey uses a novel combination of geophysical methodologies to identify previously overlooked foci for future volcanic activity at Masaya.<span class="Apple-converted-space">&nbsp;</span></p> 2019-04-19T12:18:15+00:00 ##submission.copyrightStatement## Interplinian effusive activity at Popocatépetl volcano, Mexico: New insights into evolution and dynamics of the plumbing system 2019-05-06T21:55:45+00:00 Martin Friedrich Mangler Julie Prytulak Guillem Gisbert Hugo Delgado-Granados Chiara Maria Petrone <p>Effusive eruptions dominate the eruptive record of many arc volcanoes and may hold crucial information about their plumbing systems, yet they are underrepresented in geochemical and petrological studies. Here, we present whole rock major and trace element data as well as Sr–Nd–Hf isotopic compositions for 14 lava flows and four Plinian eruptions of the Popocatépetl Volcanic Complex (PVC) in the last ~23.5 ka, allowing the first comprehensive geochemical characterisation of the dynamics and evolution of its plumbing system.&nbsp;Lavas and pumices of the PVC are andesites–dacites with a narrow compositional range showing no first-order geochemical trends in the last ~23.5 ka. Trace element and isotope ratios show that PVC magmas are derived from a depleted mantle source with a component of subducted sediments. Assimilation-fractional crystallisation models show that magma compositions are modified to varying degrees by assimilation of lower and upper crust en route to the surface. In the shallow plumbing system, geochemically distinct magmas coexist and undergo extensive mixing and hybridisation, thus buffering erupted whole rock compositions. Only few flank eruptions sample more primitive magmas from deeper reservoirs that circumvented the shallow plumbing system. Some Plinian eruptions caused compositional shifts reflecting reconfigurations of the plumbing system, which also affected subsequent effusive eruptions. Our study thus shows that the geochemical variability of PVC magmas in the last ~23.5 ka is dominated by crustal processes, and magma hybridisation is the primary mechanism to produce the buffered whole rock compositions of the PVC.</p> 2019-05-06T13:42:09+00:00 ##submission.copyrightStatement## Halogen (Cl, F) release during explosive, effusive, and intrusive phases of the 2011 rhyolitic eruption at Cordón Caulle volcano (Chile) 2019-05-11T21:34:02+00:00 C Ian Schipper Jonathan M Castro Ben M Kennedy Bruce W Christenson Alessandro Aiuppa Brent Alloway Pablo Forte Gilles Seropian Hugh Tuffen <p>We investigate sulphur, chlorine and fluorine release during explosive, effusive and intrusive phases the 2011 Cordón Caulle eruption, with a focus on halogen devolatilization. Petrological analysis shows halogen release to have been promoted by isobaric crystallization in slowly-cooled magma that was emplaced in a lava flow and sub-vent intrusion. Fluorine in particular mobilized only after extensive groundmass crystallization and incipient devitrification. By 2017, the gas emitted from vent-proximal fumaroles had hydrothermal compositions, with HCl/HF ratios decreasing with decreasing temperature. We estimate that the eruption could eventually emit up to 0.84 Mt of SO<sub>2</sub>, 6.3 Mt of HCl, and 1.9 Mt of HF, but only ~7% and ~2% of total HCl and HF were emitted during explosive phases, and significant halogens are yet to be released from the intrusion. Halogen devolatilization and its associated hazards can persist long after the cessation of rhyolite eruptions with complex magma emplacement mechanisms.</p> 2019-05-11T20:54:02+00:00 ##submission.copyrightStatement##