443 research outputs found
The evolution and storage of primitive melts in the Eastern Volcanic Zone of Iceland: the 10 ka GrĂmsvötn tephra series (i.e. the Saksunarvatn ash)
Major, trace and volatile elements were measured in a suite of primitive macrocrysts and melt inclusions from the thickest layer of the 10 ka GrĂmsvötn tephra series (i.e. Saksunarvatn ash) at Lake HvĂtĂĄrvatn in central Iceland. In the absence of primitive tholeiitic eruptions (MgO > 7 wt%) within the Eastern Volcanic Zone (EVZ) of Iceland, these crystal and inclusion compositions provide an important insight into magmatic processes in this volcanically productive region. Matrix glass compositions show strong similarities with glass compositions from the AD 1783â1784 Laki eruption, confirming the affinity of the tephra series with the GrĂmsvötn volcanic system. Macrocrysts can be divided into a primitive assemblage of zoned macrocryst cores (An78âAn92, Mg#cpx = 82â87, Fo79.5âFo87) and an evolved assemblage consisting of unzoned macrocrysts and the rims of zoned macrocrysts (An60âAn68, Mg#cpx = 71â78, Fo70âFo76). Although the evolved assemblage is close to being in equilibrium with the matrix glass, trace element disequilibrium between primitive and evolved assemblages indicates that they were derived from different distributions of mantle melt compositions. Juxtaposition of disequilibrium assemblages probably occurred during disaggregation of incompatible trace element-depleted mushes (mean La/Ybmelt = 2.1) into aphyric and incompatible trace element-enriched liquids (La/Ybmelt = 3.6) shortly before the growth of the evolved macrocryst assemblage. Post-entrapment modification of plagioclase-hosted melt inclusions has been minimal and high-Mg# inclusions record differentiation and mixing of compositionally variable mantle melts that are amongst the most primitive liquids known from the EVZ. Coupled high-field strength element (HFSE) depletion and incompatible trace element enrichment in a subset of primitive plagioclase-hosted melt inclusions can be accounted for by inclusion formation following plagioclase dissolution driven by interaction with plagioclase-undersaturated melts. Thermobarometric calculations indicate that final crystalâmelt equilibration within the evolved assemblage occurred at ~1140 °C and 0.0â1.5 kbar. Considering the large volume of the erupted tephra and textural evidence for rapid crystallisation of the evolved assemblage, 0.0â1.5 kbar is considered unlikely to represent a pressure of long-term magma accumulation and storage. Multiple thermometers indicate that the primitive assemblage crystallised at high temperatures of 1240â1300 °C. Different barometers, however, return markedly different crystallisation depth estimates. Raw clinopyroxeneâmelt pressures of 5.5â7.5 kbar conflict with apparent melt inclusion entrapment pressures of 1.4 kbar. After applying a correction derived from published experimental data, clinopyroxeneâmelt equilibria return mid-crustal pressures of 4 ± 1.5 kbar, which are consistent with pressures estimated from the major element content of primitive melt inclusions. Long-term storage of primitive magmas in the mid-crust implies that low CO2 concentrations measured in primitive plagioclase-hosted inclusions (262â800 ppm) result from post-entrapment CO2 loss during transport through the shallow crust. In order to reconstruct basaltic plumbing system geometries from petrological data with greater confidence, mineralâmelt equilibrium models require refinement at pressures of magma storage in Iceland. Further basalt phase equilibria experiments are thus needed within the crucial 1â7 kbar range
Recommended from our members
Atmospheric processes affecting the separation of volcanic ash and SO2 in volcanic eruptions: inferences from the May 2011 GrĂmsvötn eruption
The separation of volcanic ash and sulfur dioxide
(SO2) gas is sometimes observed during volcanic eruptions.
The exact conditions under which separation occurs are not
fully understood but the phenomenon is of importance because
of the effects volcanic emissions have on aviation, on
the environment, and on the earthâs radiation balance. The
eruption of GrĂmsvötn, a subglacial volcano under the Vatnajökull
glacier in Iceland during 21â28 May 2011 produced
one of the most spectacular examples of ash and SO2 separation,
which led to errors in the forecasting of ash in the
atmosphere over northern Europe. Satellite data from several
sources coupled with meteorological wind data and photographic
evidence suggest that the eruption column was unable
to sustain itself, resulting in a large deposition of ash,
which left a low-level ash-rich atmospheric plume moving
southwards and then eastwards towards the southern Scandinavian
coast and a high-level predominantly SO2 plume travelling
northwards and then spreading eastwards and westwards.
Here we provide observational and modelling perspectives
on the separation of ash and SO2 and present quantitative
estimates of the masses of ash and SO2 that erupted,
the directions of transport, and the likely impacts. We hypothesise
that a partial column collapse or âsloughingâ fed
with ash from pyroclastic density currents (PDCs) occurred
during the early stage of the eruption, leading to an ash-laden
gravity intrusion that was swept southwards, separated from
the main column. Our model suggests that water-mediated
aggregation caused enhanced ash removal because of the
plentiful supply of source water from melted glacial ice and
from entrained atmospheric water. The analysis also suggests
that ash and SO2 should be treated with separate source
terms, leading to improvements in forecasting the movement
of both types of emissions
Diffusive over-hydration of olivine-hosted melt inclusions
The pre-eruptive water content of magma is often estimated using crystal-hosted melt inclusions. However, olivine-hosted melt inclusions are prone to post-entrapment modification by H+ diffusion as they re-equilibrate with their external environment. This effect is well established for the case of H+ loss from olivine-hosted inclusions that have cooled slowly in degassed magma. Here we present evidence for the opposite effect: the addition of H+ into inclusions that are held in melts that are enriched in H2O with respect to the trapped melts. The compositional variability in a suite of 211 olivine-hosted inclusions from the Laki and Skuggafjöll eruptions in Iceland's Eastern Volcanic Zone indicates that diffusive H+ gain governs the H2O content of incompatible trace element depleted inclusions. Individual eruptive units contain olivine-hosted inclusions with widely varying incompatible element concentrations but near-constant H2O. Furthermore, over 40% of the inclusions have H2O/Ce>380H2O/Ce>380, significantly higher than the H2O/Ce expected in primary Icelandic melts or mid-ocean ridge basalts (150â280). The fact that the highest H2O/Ce ratios are found in the most incompatible element depleted inclusions indicates that hydration is a consequence of the concurrent mixing and crystallisation of compositionally diverse primary melts. Hydration occurs when olivines containing depleted inclusions with low H2O contents are juxtaposed against more hydrous melts during mixing. Melt inclusions from a single eruption may preserve evidence of both diffusive H+ loss and H+ gain. Trace element data are therefore vital for determining H2O contents of melt inclusions at the time of inclusion trapping and, ultimately, the H2O content of the mantle source regions
Tracking timescales of short-term precursors to large basaltic fissure eruptions through FeâMg diffusion in olivine
Petrological constraints on the timescales of pre-eruptive crystal storage and magma degassing provide an important framework for the interpretation of seismic, geodetic and gas monitoring data in volcanically active regions. We have used FeâMg diffusion chronometry in 86 olivine macrocrysts from the AD 1783â1784 Laki eruption on Iceland's Eastern Volcanic Zone to characterise timescales of crystal storage and transport in the lead-up to this eruption. The majority of these olivines have core compositions of Fo 81 olivines record FeâMg diffusion timescales of âŒ124 days; these crystals are likely to have formed in mid-crustal magma chambers, been transferred to storage at shallower levels and then entrained into the Laki melt prior to eruption. Typical FeâMg diffusion timescales of 6â10 days are shorter than the average time interval between discrete episodes of the Laki eruption, indicating variable or pulsed disaggregation of stored crystals into the carrier liquid prior to the onset of each episode. The diffusion timescales coincide with historical accounts of strong and frequent earthquakes in southeast Iceland, which we interpret as being associated with mush disaggregation related to melt withdrawal and the initiation of dyke propagation from a crustal magma reservoir at âŒ6 ± 3 km depth to the surface. We calculate pre-eruptive CO2 fluxes of 2â6 Mtâdâ1, assuming a pre-eruptive CO2 outgassing budget of 189.6 Mt for the Laki eruption and a constant rate of CO2 release in the 6â10 days preceding each eruptive episode. Our dataset indicates that petrological constraints on the timescales of magmatic processes occurring in the days leading up to historic eruptions may enhance our ability to forecast the onset of future large eruptions, both in Iceland and further afield
The Giant Lavas of Kalkarindji: rubbly pÄhoehoe lava in an ancient continental flood basalt province
The Kalkarindji continental flood basalt province of northern Australia erupted in the mid Cambrian (c. 511-505 Ma). It now consists of scattered basaltic lava fields, the most extensive being the Antrim Plateau Volcanics (APV) - a semi-continuous outcrop (c. 50,000 km2) reaching a maximum thickness of 1.1 km. Cropping out predominately in the SW of the APV, close to the top of the basalt succession, lies the Blackfella Rockhole Member (BRM). Originally described as âbasaltic agglomerateâ the BRM has, in recent years, been assumed to be explosive tephra of phreatomagmatic origin, thus providing a potent vehicle for volatile release to the upper atmosphere. Our detailed field investigations reveal that this basaltic agglomerate is, in reality, giant rubble collections (15 - 20 m thick) forming the upper crusts of rubbly pÄhoehoe lava units 25 - 40 m thick; covering 18,000 - 72,000 km2 and an estimated volume of 1,500 - 19,200 km3. These flows, rheologically but not chemically, distinct from the majority of Kalkarindji lavas, indicate a fundamental change in eruption dynamics. A low volatile content, induced high amounts of pre-eruptive degassing causing super-cooling and an increase in crystal nucleation and viscosity. A more viscous lava and a consistently faster rate of effusion (analogous to that of Laki, Iceland) created the flow dynamics necessary to disturb the lava crust to the extent seen in the BRM. Volatile release is estimated at 1.65 x 104 - 2.11 x 105 Tg total CO2 at a rate of 867 Tg a- 1 and 9.07 x 103 - 1.16 x 105 Tg SO2 at 476.50 Tg a- 1. These masses accounted for 0.5% of Cambrian atmospheric conditions whilst limiting factors reduced the effect of volatile delivery to the atmosphere, thus any potential global impact caused by these flows alone was minimal
Recommended from our members
Landscape evolution associated with the 2014â2015 Holuhraun eruption in Iceland
The 2014â2015 Holuhraun eruption in Iceland developed between the outlet glacier Dyngjujökull and the Askja central volcano and extruded a bulk lava volume of over 1âŻkm3 onto the floodplain of the JökulsĂĄ ĂĄ Fjöllum river, making it the largest effusive eruption in Iceland during the past 230 years. Time-series monitoring using a combination of traditional aerial imaging, unmanned aerial systems, and field-based geodetic surveys, established an unprecedented record of the hydrological response of the river system to this lava flow. We observed: (1) the formation of lava-dammed lakes and channels produced during dam-breaching events; (2) percolation of glacial meltwater into the porous and permeable lava, forming an ephemeral hydrothermal system that included hot pools and hot springs that emerged from the lava flow front; and (3) the formation of new seepage channels caused by upwelling of water around the periphery of the lava flow. The observations show that lava flows, like the one produced by the 2014â2015 Holuhraun eruption, can cause significant hydrological changes that continue for several years after the lava is emplaced. Documenting these processes is therefore crucial for our interpretation of volcanic landscapes and processes of lavaâwater interaction on both Earth and Mars
A Liposome-Micelle-Hybrid (LMH) Oral Delivery System for Poorly Water-Soluble Drugs: Enhancing Solubilisation and Intestinal Transport
A novel liposome-micelle-hybrid (LMH) carrier system was developed as a superior oral drug delivery platform compared to conventional liposome or micelle formulations. The optimal LMH system was engineered by encapsulating TPGS micelles in the aqueous core of liposomes and its efficacy for oral delivery was demonstrated using lovastatin (LOV) as a model poorly soluble drug with P-gp (permeability glycoprotein) limited intestinal absorption. LOV-LMH was characterised as unilamellar, spherical vesicles encapsulating micellar structures within the interior aqueous core and showing an average diameter below 200 nm. LMH demonstrated enhanced drug loading, water apparent solubility and extended/controlled release of LOV compared to conventional liposomes and micelles. LMH exhibited enhanced LOV absorption and transportation in a Caco-2 cell monolayer model of the intestine by inhibiting the P-gp transporter system compared to free LOV. The LMH system is a promising novel oral delivery approach for enhancing bioavailability of poorly water-soluble drugs, especially those presenting P-gp effluxes limited absorption
Intra-articular calcaneal fracture: closed reduction and balloon-assisted augmentation with calcium phosphate cement: a case report
Ash generation and distribution from the April-May 2010 eruption of Eyjafjallajökull, Iceland
The 39-day long eruption at the summit of Eyjafjallajökull volcano in AprilâMay 2010 was of modest size but ash was widely dispersed. By combining data from ground surveys and remote sensing we show that the erupted material was 4.8±1.2·1011â
kg (benmoreite and trachyte, dense rock equivalent volume 0.18±0.05â
km3). About 20% was lava and water-transported tephra, 80% was airborne tephra (bulk volume 0.27â
km3) transported by 3â10â
km high plumes. The airborne tephra was mostly fine ash (diameter <1000 ”m). At least 7·1010â
kg (70â
Tg) was very fine ash (<28 ”m), several times more than previously estimated via satellite retrievals. About 50% of the tephra fell in Iceland with the remainder carried towards south and east, detected over ~7 million km2 in Europe and the North Atlantic. Of order 1010â
kg (2%) are considered to have been transported longer than 600â700â
km with <108â
kg (<0.02%) reaching mainland Europe
Satellite detection, long-range transport, and air quality impacts of volcanic sulfur dioxide from the 2014â2015 flood lava eruption at BĂĄrĂ°arbunga (Iceland)
The 2014â2015 BĂĄrĂ°arbunga-VeiĂ°ivötn fissure eruption at Holuhraun produced about 1.5âkm3 of lava, making it the largest eruption in Iceland in more than 200âyears. Over the course of the eruption, daily volcanic sulfur dioxide (SO2) emissions exceeded daily SO2 emissions from all anthropogenic sources in Europe in 2010 by at least a factor of 3. We present surface air quality observations from across Northern Europe together with satellite remote sensing data and model simulations of volcanic SO2 for September 2014. We show that volcanic SO2 was transported in the lowermost troposphere over long distances and detected by air quality monitoring stations up to 2750âkm away from the source. Using retrievals from the Ozone Monitoring Instrument (OMI) and the Infrared Atmospheric Sounding Interferometer (IASI), we calculate an average daily SO2 mass burden of 99â±â49 kilotons (kt) of SO2 from OMI and 61â±â18âkt of SO2 from IASI for September 2014. This volcanic burden is at least a factor of 2 greater than the average SO2 mass burden between 2007 and 2009 due to anthropogenic emissions from the whole of Europe. Combining the observational data with model simulations using the United Kingdom Met Office's Numerical Atmospheric-dispersion Modelling Environment model, we are able to constrain SO2 emission rates to up to 120âkilotons per day (kt/d) during early September 2014, followed by a decrease to 20â60âkt/d between 6 and 22 September 2014, followed by a renewed increase to 60â120âkt/d until the end of September 2014. Based on these fluxes, we estimate that the eruption emitted a total of 2.0â±â0.6âTg of SO2 during September 2014, in good agreement with ground-based remote sensing and petrological estimates. Although satellite-derived and model-simulated vertical column densities of SO2 agree well, the model simulations are biased low by up to a factor of 8 when compared to surface observations of volcanic SO2 on 6â7 September 2014 in Ireland. These biases are mainly due to relatively small horizontal and vertical positional errors in the simulations of the volcanic plume occurring over transport distances of thousands of kilometers. Although the volcanic air pollution episodes were transient and lava-dominated volcanic eruptions are sporadic events, the observations suggest that (i) during an eruption, volcanic SO2 measurements should be assimilated for near real-time air quality forecasting and (ii) existing air quality monitoring networks should be retained or extended to monitor SO2 and other volcanic pollutants
- âŠ