The magmatic and eruptive evolution of the 1883 caldera-forming eruption of Krakatau: Integrating field- to crystal-scale observations

Explosive, caldera-forming eruptions are exceptional and hazardous volcanic phenomena. The 1883 eruption of Krakatau is the largest such event for which there are detailed contemporary written accounts, allowing information on the eruptive progression to be integrated with the stratigraphy and geochemistry of its products. Freshly exposed sequences of the 1883 eruptive deposits of Krakatau, stripped of vegetation by a tsunami generated by the flank collapse of Anak Krakatau in 2018, shed new light on the eruptive sequence. Matrix glass from the base of the stratigraphy is chemically distinct and more evolved than the overlying sequence indicating the presence of a shallow, silicic, melt-rich region that was evacuated during the early eruptive activity from May 1883 onwards. Disruption of the shallow, silicic magma may have led to the coalescence and mixing of chemically similar melts representative of a range of magmatic conditions, as evidenced by complex and varied plagioclase phenocryst zoning profiles. This mixing, over a period of two to three months, culminated in the onset of the climactic phase of the eruption on 26th August 1883. Pyroclastic density currents (PDCs) emplaced during this phase of the eruption show a change in transport direction from north east to south west, coinciding with the deposition of a lithic lag breccia unit. This may be attributed to partial collapse of an elevated portion of the island, resulting in the removal of a topographic barrier. Edifice destruction potentially further reduced the overburden on the underlying magmatic system, leading to the most explosive and energetic phase of the eruption in the morning of 27th August 1883. This phase of the eruption culminated in a final period of caldera collapse, which is recorded in the stratigraphy as a second lithic lag breccia. The massive PDC deposits emplaced during this final phase contain glassy blocks up to 8 m in size, observed for the first time in 2019, which are chemically similar to the pyroclastic sequence. These blocks are interpreted as representing stagnant, shallow portions of the magma reservoir disrupted during the final stages of caldera formation. This study provides new evidence for the role that precursory eruptions and amalgamation of shallow crustal magma bodies potentially play in the months leading up to caldera-forming eruptions

Explosive volcanic activity on Venus: The roles of volatile contribution, degassing, and external environment

We investigate the conditions that will promote explosive volcanic activity on Venus. Conduit processes were simulated using a steady-state, isothermal, homogeneous flow model in tandem with a degassing model. The response of exit pressure, exit velocity, and degree of volatile exsolution was explored over a range of volatile concentrations (H2O and CO2), magma temperatures, vent altitudes, and conduit geometries relevant to the Venusian environment. We find that the addition of CO2 to an H2O-driven eruption increases the final pressure, velocity, and volume fraction gas. Increasing vent elevation leads to a greater degree of magma fragmentation, due to the decrease in the final pressure at the vent, resulting in a greater likelihood of explosive activity. Increasing the magmatic temperature generates higher final pressures, greater velocities, and lower final volume fraction gas values with a correspondingly lower chance of explosive volcanism. Cross-sectionally smaller, and/or deeper, conduits were more conducive to explosive activity. Model runs show that for an explosive eruption to occur at Scathach Fluctus, at Venus’ mean planetary radius (MPR), 4.5% H2O or 3% H2O with 3% CO2 (from a 25 m radius conduit) would be required to initiate fragmentation; at Ma’at Mons (~9 km above MPR) only ~2% H2O is required. A buoyant plume model was used to investigate plume behaviour. It was found that it was not possible to achieve a buoyant column from a 25 m radius conduit at Scathach Fluctus, but a buoyant column reaching up to ~20 km above the vent could be generated at Ma’at Mons with an H2O concentration of 4.7% (at 1300 K) or a mixed volatile concentration of 3% H2O with 3% CO2 (at 1200 K). We also estimate the flux of volcanic gases to the lower atmosphere of Venus, should explosive volcanism occur. Model results suggest explosive activity at Scathach Fluctus would result in an H2O flux of ~107 kg s-1. Were Scathach Fluctus emplaced in a single event, our model suggests that it may have been emplaced in a period of ~15 days, supplying 1-2 x 104 Mt H2O to the atmosphere locally. An eruption of this scale might increase local atmospheric H2O abundance by several ppm over an area large enough to be detectable by near-infrared nightside sounding using the 1.18 µm spectral window such as that carried out by the Venus Express/VIRTIS spectrometer. Further interrogation of the VIRTIS dataset is recommended to search for ongoing volcanism on Venus

Multi-system neurological disease is common in patients with OPA1 mutations

Additional neurological features have recently been described in seven families transmitting pathogenic mutations in OPA1, the most common cause of autosomal dominant optic atrophy. However, the frequency of these syndromal ‘dominant optic atrophy plus’ variants and the extent of neurological involvement have not been established. In this large multi-centre study of 104 patients from 45 independent families, including 60 new cases, we show that extra-ocular neurological complications are common in OPA1 disease, and affect up to 20% of all mutational carriers. Bilateral sensorineural deafness beginning in late childhood and early adulthood was a prominent manifestation, followed by a combination of ataxia, myopathy, peripheral neuropathy and progressive external ophthalmoplegia from the third decade of life onwards. We also identified novel clinical presentations with spastic paraparesis mimicking hereditary spastic paraplegia, and a multiple sclerosis-like illness. In contrast to initial reports, multi-system neurological disease was associated with all mutational subtypes, although there was an increased risk with missense mutations [odds ratio = 3.06, 95% confidence interval = 1.44–6.49; P = 0.0027], and mutations located within the guanosine triphosphate-ase region (odds ratio = 2.29, 95% confidence interval = 1.08–4.82; P = 0.0271). Histochemical and molecular characterization of skeletal muscle biopsies revealed the presence of cytochrome c oxidase-deficient fibres and multiple mitochondrial DNA deletions in the majority of patients harbouring OPA1 mutations, even in those with isolated optic nerve involvement. However, the cytochrome c oxidase-deficient load was over four times higher in the dominant optic atrophy + group compared to the pure optic neuropathy group, implicating a causal role for these secondary mitochondrial DNA defects in disease pathophysiology. Individuals with dominant optic atrophy plus phenotypes also had significantly worse visual outcomes, and careful surveillance is therefore mandatory to optimize the detection and management of neurological disability in a group of patients who already have significant visual impairment

US hegemony and the origins of Japanese nuclear power : the politics of consent

This paper deploys the Gramscian concepts of hegemony and consent in order to explore the process whereby nuclear power was brought to Japan. The core argument is that nuclear power was brought to Japan as a consequence of US hegemony. Rather than a simple manifestation of one state exerting material ‘power over' another, bringing nuclear power to Japan involved a series of compromises worked out within and between state and civil society in both Japan and the USA. Ideologies of nationalism, imperialism and modernity underpinned the process, coalescing in post-war debates about the future trajectory of Japanese society, Japan's Cold War alliance with the USA and the role of nuclear power in both. Consent to nuclear power was secured through the generation of a psychological state in the public mind combining the fear of nuclear attack and the hope of unlimited consumption in a nuclear-fuelled post-modern world

US Cosmic Visions: New Ideas in Dark Matter 2017: Community Report

This white paper summarizes the workshop "U.S. Cosmic Visions: New Ideas in Dark Matter" held at University of Maryland on March 23-25, 2017

Strong responses of Southern Ocean phytoplankton communities to volcanic ash

Volcanic eruptions have been hypothesized as an iron supply mechanism for phytoplankton blooms; however, little direct evidence of stimulatory responses has been obtained in the field. Here we present the results of twenty-one 1–2?day bottle enrichment experiments from cruises in the South Atlantic and Southern Ocean which conclusively demonstrated a photophysiological and biomass stimulation of phytoplankton communities following supply of basaltic or rhyolitic volcanic ash. Furthermore, experiments in the Southern Ocean demonstrated significant phytoplankton community responses to volcanic ash supply in the absence of responses to addition of dissolved iron alone. At these sites, dissolved manganese concentrations were among the lowest ever measured in seawater, and we therefore suggest that the enhanced response to ash may have been a result of the relief of manganese (co)limitation. Our results imply that volcanic ash deposition events could trigger extensive phytoplankton blooms, potentially capable of significant impacts on regional carbon cycling

Geology, petrology and geochemistry of the dome complex of Huequi volcano, southern Chile

Huequi, a little-known volcano in the southern part of the Andean southern volcanic zone (SSVZ), shows a regionally unusual eruption style, mineralogy and geochemistry. The volcano comprises multiple highly-eroded lava domes. Past eruptions were accompanied by relatively minor explosive activity, most recently from 1890-1920. The rocks erupted by Huequi range from basaltic andesite to dacite, and are highly distinctive when compared to other volcanoes of the SSVZ, being K-poor and Al-rich, and containing euhedral hornblende phenocrysts. Overall compositions suggest a notably water-rich magma source, evolving through high levels of fractionation and subsequent degassing to produce highly porphyritic dome-forming andesites. The ultimate causes of water-rich magmas at this point in the arc remain unclear

Vulcanian explosion cycles: patterns and predictability

Repetitive and violent Vulcanian explosion sequences are common hazards at many volcanoes. Statistical analyses of such sequences form the basis of forecasting models and reveal underlying explosive processes. However, no single statistical model describes interexplosion repose intervals in Vulcanian systems. Soufrière Hills, Montserrat, is best described by a log-logistic model, while Sakurajima, Japan, shows a transition from a log-logistic to a Weibull model as activity intensifies. Anak Krakatau, Indonesia, displays two failure modes on different time scales, both described by Weibull distributions. At the Kameni Islands, Santorini, Greece, model-fitting parameters vary between eruption cycles. Rates of magma rise and pressurization may be the most important controls in determining the statistical distribution of repose intervals in Vulcanian systems