Changes from effusive to explosive behavior are common during single eruptive events. However, in many cases these shifts are recorded between distinct eruptions, separated by periods of volcanic ...repose. In the quiescent periods, magma chamber processes are likely to play a major role in controlling the style of the next eruption, by modifying the properties of the magmas. Crystallinity, viscosity, dissolved water content and the water saturation state of the melt are among the properties that can easily change during periods of repose, and that can influence the behavior of the magmas during eruption. Here, we focus on the active Nisyros-Yali volcanic center (South Aegean Volcanic Arc) to investigate the water saturation state of the magma reservoir, before effusive and explosive events were triggered. We investigate the evolution of Cl in melt inclusions, and the fractionation of Cl from F in apatite included in other mineral phases. We present an analytical protocol for minimizing F diffusion during EPMA apatite measurements, and to correct for diffusion resulting from variable crystal orientation. The relatively high concentrations of Cl positively correlated with the degree of differentiation in melt inclusions, and the lack of a clear fractionation trend of Cl from F in apatite, indicate that explosive eruptions were generated by magmas that were water-undersaturated during magmatic storage. In effusive eruptions, both melt and apatite inclusions record Cl depletion at magmatic storage conditions. This suggests that effusive events were generated by magmas stored in areas of the reservoir with sufficient volumes of exsolved water to significantly extract Cl from the melt. This is in accordance with mineral-melt hygrometry estimates, which suggest dissolved water contents of ~4.5 wt% for magmas generating explosive events, and in excess of 5.5 wt% for magmas behaving effusively. The presence of exsolved volatiles in the magma reservoirs immediately prior to eruption favors outgassing in the conduit and effusive behavior despite the high water content. This is partly due to increasing the compressibility of the magmatic reservoir upon mafic recharge, and partly due to fostering the development of early gas permeability, at deep levels in the conduit.
The concentration of pre-eruptive volatiles is a key parameter that controls the eruptive behaviour of volcanoes. Among these, water is the most abundant volatile and has a major influence on magma ...chamber dynamics and a primary role in driving eruptions. While accurately quantifying the pre-eruptive dissolved water concentration of magmas is a crucial step in understanding eruptive styles, we still encounter problems in this regard. One of the main challenges is in discriminating pristine melt inclusions from those that lost water due to syneruptive and post-emplacement processes. To this end, we have calibrated a Fourier Transform Infrared (FTIR) setup with a Germanium crystal objective for Attenuated Total Reflectance analyses (ATR) coupled to a Focal-Plane Array detector (FPA), which allows the measurement of single-sided polished rhyolitic melt inclusions. The samples do not require any other special preparation routine, making it a versatile method (i.e. it can be applied to samples prepared for microprobe analysis). The setup generates high-resolution (4 μm) water distribution images that allow the quantification of dissolved water with an uncertainty of ±0.35 wt%. Water diffusion inside the melt inclusions can be identified on the spectral images, allowing for a qualitative analysis that, in most cases, can easily distinguish between pristine and degassed inclusions. We apply this setup to eight units (four explosive and four effusive) from the Nisyros-Yali volcanic center, in the South Aegean Sea, and compare the results with previously published hygrometry data. The results show that even in explosive units, which are generally considered unaffected by gas loss, up to 75% of the melt inclusions lost water. Because of this, the measured water contents show a spread over a range of ~2 wt%. Dissolved water contents in pristine melt inclusions match those from previous hygrometry calculations, indicating ~4 to 5 wt% H2O. In effusive units, all the melt inclusions are degassed, yielding water contents that vary from 0 to 3.6 wt%, as compared to ~5.6 wt% H2O given by mineral-melt hygrometry. The new setup and calibration provide a fast and cheap way for measuring water contents in calc-alkaline rhyolitic melt inclusions. Furthermore, our results indicate the importance of determining the pristine versus degassed nature of inclusions before any interpretations are made.
Water-rich silicic magmas are capable of erupting effusively and explosively, and this drastic change in eruptive styles, termed effusive-explosive transition, has important implications in managing ...volcanic hazards. Some volcanoes exhibit effusive-explosive transitions during the same eruptive event, while others show this behavior between different eruptions. In the latter case, magma chamber processes induce physical-chemical changes in the magma, which can favor either effusivity or explosivity. This is the case for the Nisyros-Yali volcanic center, from the South Aegean Sea. In the recent stages of activity (past 120 ky), the volcanic area generated eight rhyolitic effusive and explosive events (five on the island of Nisyros and three on the island of Yali), including two caldera-forming eruptions. Changes of water content, temperature and pre-eruptive water-saturation between effusive and explosive deposits point to a potential time-dependency between the two eruptive styles. We investigate this time-dependency by applying UTh disequilibrium dating to zircon crystals. Our eruptive age estimates of the investigated units range from 118.7 ± 10 ka to 19.9 ± 1.5 ka for Nisyros, and from 40 ± 5.2 ka to 22.7 ± 1.6 ka for Yali. Yali volcano has developed after the two caldera-forming events on Nisyros, which occurred at 63.1 ± 4.7 ka and 58.4 ± 2.7 ka. Yali marks the transition to a more geometrically complex system, where the upper-crustal silicic mush hosts at least two eruptible magma chambers (one under Yali, and one under Nisyros). The eruptive styles at both volcanoes seem to be correlated with the length of the repose periods. Effusive events occur after longer periods of volcanic quiescence, while explosive events are generated after shorter periods of repose of ~5–10 ky, which can be extended based on eruption age uncertainty to <18 ky for Nisyros and <12 ky for Yali. This observation is explained by the physical state of the volatiles in the magma chamber, with longer repose periods favoring volatile build-up. This can lead to water-supersaturation at storage pressures which was shown to favor effusivity. Based on this interpretation, both Nisyros and Yali volcanoes are presently in the effusive time window, which makes it probable for the next eruptions to be non-explosive.
Arc volcanoes generally emit water-rich, high-viscosity silicic magmas, which are prone to erupt explosively. However, effusive behavior is a common occurrence despite the high-H2O, high viscosity ...conditions. The contrasting shift from effusive to explosive behavior (and vice-versa) at any individual volcano raises the question on what controls eruptive style. Permeability development in conduits allows magma to outgas and is clearly a key factor. However, an important question is whether magma reservoir processes can also have an influence on eruptive styles. The answer could have direct impact on predicting eruptive behavior. Hence, we explore this potential connection by analyzing nine alternating effusive and explosive silicic deposits that were emplaced during distinct eruptions at the active Nisyros-Yali volcanic center. The lavas and pyroclastic deposits are compositionally similar. This indicates a negligible influence of the bulk rock composition on different eruptive styles. The crystal contents vary between units, without any clear correlation with eruptive style (from nearly aphyric to ~45 vol% crystals). Mineral textures and chemistry do show variations between effusive and explosive eruptions, with a larger proportion of resorbed plagioclase and, in most cases, more evolved amphiboles present in the lava flows. Mineral thermo-barometry and hygrometry show that the storage zones of magmas generating effusive eruptions evolved towards colder and more water-rich conditions (710–790 °C; 5.6–6.5 wt% H2O) than their explosive counterparts (815–850 °C; 4.2–4.6 wt% H2O). At storage pressures of 1.5–2 kbar, relevant for Nisyros-Yali, the volatile saturation level is reached at >5 wt% H2O. Therefore, it is likely that the magmas reached water-saturation before generating effusive eruptions, and were undersaturated before explosive events. We hypothesize that the presence of exsolved volatiles in the subvolcanic reservoir can enhance the outgassing potential of the magma during conduit ascent. Hence, the rhyolitic effusive-explosive transitions can be influenced by the pre-eruptive exsolved versus dissolved state of the volatiles in the magma chamber. This can lead to the less explosive eruptions for the most water-rich reservoir conditions.
•In water-rich silicic systems effusions can be generated by magmas with higher water contents than explosions.•The paper presents the comparative example of effusive and explosive deposits erupted at Nisyros-Yali.•Explosive eruptions were generated by water-rich magmas that were water-undersaturated during pre-eruptive storage.•Effusive eruptions were generated by water-richer magmas that were water-supersaturated during pre-eruptive storage.•The role of pre-eruptive exsolved volatiles in controlling eruptive styles is explored.
Most arc volcanoes erupt intermediate to silicic magmas that have sufficient volatile contents to behave explosively. Despite this explosive potential, low-energy effusive eruptions of such viscous ...water-rich magmas are common occurrences. Hence, predicting the style of the next eruption, with its obvious importance on hazard mitigation, remains one of the main challenges of volcanology. Here, we investigate the changes in eruptive styles at Methana volcano, from the South Aegean Arc. This volcano has generated multiple andesite-to-dacite eruptions, with the last event occurring in historical times (~2250 BP). We focus on 14 eruptive events, 3 being explosive. We compare the petrology and geochemistry of the deposits to reconstruct the magma chamber events that preceded both types of eruptions. We estimate the thermo-chemical conditions that characterized each eruptive event, and highlight the causes that promoted or inhibited magma fragmentation: temperature, pressure, composition, relative volumes of different magma batches, dissolved water content, crystallinity, melt and bulk viscosities. The results indicate that Methana harbors an upper-crustal silicic reservoir stored at ~2 kbar (likely dacitic to rhyodacitic in composition) that is in a highly crystalline state (>50 vol% crystals, mostly uneruptible). All the eruptions are triggered by deeper magma recharge ascending from storage pressures of ~4–5 kbar, leading to some rejuvenation of the shallow silicic mush. The most mafic recharges (~55 wt% SiO2, ~1000 °C, >3 wt% H2O) promote effusive eruptions after mixing and hybridizing the upper-crustal reservoir (hybrids of ~57–64 wt% SiO2, ~900–950 °C, generally 3–4 wt% H2O). Slightly colder, wetter and more differentiated recharges (~62 wt% SiO2; ~900 °C, ~4 wt% H2O) trigger explosive events after having minimal interaction with the upper-crustal reservoir. However, the dissolved water content is not the only factor influencing explosivity, as some of the wettest magmas (>4.5 wt% H2O) generate lava flows. Our data indicate that a key control on effusive-explosive transitions at Methana is the crystallinity of the erupted material. A high crystallinity (40–55 vol%) increases the bulk-viscosity, which results in the magma having a slower ascent velocity. In addition, crystallinity enhances the formation of permeable pathways for the gas. Longer ascent timescales and enhanced permeability in the conduit improve the outgassing potential of the magmas and lead to effusive behavior. The opposite occurs for explosive events. Here, the lower crystallinity of the magmas (30 vol%) translates into lower bulk-viscosities and faster ascent rates, which inhibit outgassing. This case study highlights the importance of obtaining better constraints on the state of subvolcanic magma reservoirs, in particular concerning crystallinity and volatile concentrations, which has to become a priority in the years to come.
The aim of this exploratory research is to capture spatial evolution patterns in the Bucharest metropolitan area using sets of single polarised synthetic aperture radar (SAR) satellite data and ...multi-temporal radar interferometry. Three sets of SAR data acquired during the years 1992-2010 from ERS-1/-2 and ENVISAT, and 2011-2014 from TerraSAR-X satellites were used in conjunction with the Small Baseline Subset (SBAS) and persistent scatterers (PS) high-resolution multi-temporal interferometry (InSAR) techniques to provide maps of line-of-sight displacements. The satellite-based remote sensing results were combined with results derived from classical methodologies (i.e., diachronic cartography) and field research to study possible trends in developments over former clay pits, landfill excavation sites, and industrial parks. The ground displacement trend patterns were analysed using several linear and nonlinear models, and techniques. Trends based on the estimated ground displacement are characterised by long-term memory, indicated by low noise Hurst exponents, which in the long-term form interesting attractors. We hypothesize these attractors to be tectonic stress fields generated by transpressional movements.
This work provides a comprehensive GIS mapping integrated with geological and geophysical data (magnetic and gravimetric) to reveal the interplay between (i) magmatism and volcanic activity, (ii) ...intra-mountain basin development and (iii) large-scale faulting/tectonic features in the post-collisional setting of the East Carpathians. The geological, geophysical and tectonic data of the Călimani-Gurghiu-Harghita range (CGH) confirm the contemporaneous formation of basins and volcanic activity. The two phenomena propagated southwards in time, parallel to the collisional front, in close relation to the development of the fault systems. The geometry of the faults and alignment of volcanic edifices indicate both strike-slip and normal faulting, with no rotation. The main volcanic range and main tectonic basins evolved along a regional NNW-SSE striking sinistral transtensional fault zone with left stepping stepovers and pull-apart basins in the transfer areas. The fault zones probably acted as least resistance areas that fostered the development of magma ascent paths and plumbing systems. These connected the volcanic centers with numerous magma chambers emplaced at the upper mantle – lower crust boundary and throughout the lower and upper crust. The magma generation is most likely a result of the interplay between large-scale transtensional systems that induced decompression in the previously metasomatised mantle, and asthenosphere upwelling in the post-collisional East Carpathian orogen.
•The article discusses the tectonic and structural control of post-collisional volcanism vs. typical arc volcanism.•The Călimani-Gurghiu-Harghita range is an example of post-collisional volcanism, showing ~ 160 km length.•The N-S development of tectonic structures at 10-0.03 Ma is following the mountain building processes in the East Carpathians.•The history of deformation and evolution of the stress field is combined with volume of erupted magma along the CGH.
Experimental and, retrospective, clinical data indicate that anaesthetic technique might influence the risk of metastasis after cancer surgery. Neutrophil extracellular trapping (NETosis) is an ...immunological mechanism strongly linked with increased metastatic risk. Similarly, vascular endothelial growth factor A is linked to angiogenesis implicated in recurrence. Therefore, we investigated the effect of four anaesthetic techniques on NETosis and angiogenic factors expression in women undergoing breast cancer resection.
Women (n=120) undergoing primary breast tumour resection were randomly assigned to receive one of four anaesthetics: sevoflurane (S), sevoflurane plus i.v. lidocaine (SL), propofol (P), and propofol plus i.v. lidocaine (PL). Venous blood was collected before induction and 20–28 h after operation. Neutrophil myeloperoxidase and citrullinated histone H3, biomarkers of NETosis, and biomarkers of angiogenesis were measured by enzyme-linked immunosorbent assay.
Patient characteristic data and perioperative management did not differ between study groups. The anaesthetic technique including lidocaine decreased expression of citrullinated histone H3 compared with no lidocaine (109 23 vs 125 22 ng ml−1, P=0.01 for SL and S and 98 14 vs 130 32 mg ml−1, P=0.007, for PL and P, respectively). Similarly, myeloperoxidase was decreased by lidocaine (8.5 3.4 vs 10.8 1.8 ng ml−1, P=0.03 for SL and S and 8.6 3.1 vs 11.6 2.5 ng ml−1, P=0.01 for PL and P, respectively). Lidocaine also decreased expression of matrix metalloproteinase 3 (MMP3) but not MMP9, whichever anaesthetic was used. Vascular endothelial growth factor A concentrations were not significantly influenced by the anaesthetic technique.
I.V. perioperative lidocaine decreased postoperative expression of NETosis and MMP3, regardless of general anaesthetic technique. This supports the hypothesis that i.v. lidocaine during cancer surgery of curative intent might reduce recurrence.
NCT02839668.
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