https://www.jvolcanica.org/ojs/index.php/volcanica/issue/feed Volcanica 2019-04-19T12:33:32+00:00 Jamie Farquharson farquharson@jvolcanica.org 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> https://www.jvolcanica.org/ojs/index.php/volcanica/article/view/12 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 kayla.iacovino@asu.edu Christy B Till christy.till@asu.edu <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="https://densityx.herokuapp.com/">https://densityx.herokuapp.com</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## https://www.jvolcanica.org/ojs/index.php/volcanica/article/view/24 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 g.lerner@auckland.ac.nz Shane J Cronin s.cronin@auckland.ac.nz Gillian M Turner gillian.turner@vuw.ac.nz <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## https://www.jvolcanica.org/ojs/index.php/volcanica/article/view/20 Structures controlling volcanic activity within Masaya caldera, Nicaragua 2019-04-19T12:19:00+00:00 Guillermo Caravantes González guillermo@geoarc.org Hazel Rymer h.rymer@open.ac.uk Jeffrey Zurek jeffrey_zurek@sfu.ca Susanna Ebmeier S.K.Ebmeier@leeds.ac.uk Stephen Blake stephen.blake@open.ac.uk Glyn Williams-Jones glynwj@sfu.ca <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##