火山通道岩浆流动动力学模型在天池火山喷发过程中的应用     

魏海泉  Melnik  O  刘永顺  Barmin  A  Sparks  RSJ 《岩石学报》2006,22(12):3007-3013

在圆柱形火山通道的下部,岩浆上升速度与岩浆粘度、密度及压力有关。这时的流体动力学过程可以应用一般的牛顿流体模型。火山通道中部气泡化岩浆上升时,液相和气相的转化符合质量守恒方程,混合相总体符合动量守恒方程。其中气泡形成与生长过程符合达西定律与数密度方程。在火山通道靠上部的碎屑化带里,不同组分符合质量守恒方程,混合相总体符合动量守恒方程。天池火山千年大喷发时,通道直径是62m。岩浆房内的岩浆含有约3%体积百分数的气泡,气泡体积在65%时岩浆破碎,颗粒离开通道时的速度是145ms~(-1),而气体离开通道时的速度是170ms~(-1)。气体颗粒分散相出口压力是12.2MPa。在破火山口塌陷之前,岩浆房内气泡体积可高达30%～40%。与此同时,碎屑化发生时岩浆的孔隙度也增加到70%～75%左右。这时的出口压力降低至7～8MPa,出口气体速度增加到180ms~(-1)。气象站碱流质寄生火山喷发对应的喷发通道直径是40m,喷发以气体出口速度15～25ms~(-1)的弱爆破性喷发和侵出式喷发为特征。这时浮岩的孔隙度比千年大喷发的孔隙度低,为48%～61%,而浮岩密度高,为1.01～1.35gcm~(-3)。在侵出相喷发时最高释放率可以达到42m~3s~(-1)(致密岩石当量 DRE),孔隙度变化范围是70%～80%。  相似文献   

Shallow-level decompression crystallisation and deep magma supply at Shiveluch Volcano   总被引：1，自引：0，他引：1  

M. C. S. Humphreys  J. D. Blundy  R. S. J. Sparks 《Contributions to Mineralogy and Petrology》2008,155(1):45-61

Recent petrological studies indicate that some crustal magma chambers may be built up slowly by the intermittent ascent and amalgamation of small packets of magma generated in a deep-seated source region. Despite having little effect on whole-rock compositions, this process should be detectable as variable melt trace element composition, preserved as melt inclusions trapped in phenocrysts. We studied trace element and H₂O contents of plagioclase- and hornblende-hosted melt inclusions from andesite lavas and pumices of Shiveluch Volcano, Kamchatka. Melt inclusions are significantly more evolved than the whole rocks, indicating that the whole rocks contain a significant proportion of recycled foreign material. H₂O concentrations indicate trapping at a wide range of pressures, consistent with shallow decompression-driven crystallisation. The variation of trace element concentrations indicates up to ∼30% decompression crystallisation, which accounts for crystallisation of the groundmass and rims on phenocrysts. Trace element scatter could be explained by episodic stalling during shallow magma ascent, allowing incompatible element concentrations to increase during isobaric crystallisation. Enrichment of Li at intermediate pH₂O reflects influx and condensation of metal-rich vapours. A set of “exotic melts”, identified by their anomalous incompatible trace element characteristics, indicate variable source chemistry. This is consistent with evolution of individual magma batches with small differences in trace element chemistry, and intermittent ascent of magma pulses. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

Periodic density functional theory calculations of bulk and the (010) surface of goethite     

James D Kubicki  Kristian W Paul  Donald L Sparks 《Geochemical transactions》2008,9(1):4

Background  

Goethite is a common and reactive mineral in the environment. The transport of contaminants and anaerobic respiration of microbes are significantly affected by adsorption and reduction reactions involving goethite. An understanding of the mineral-water interface of goethite is critical for determining the molecular-scale mechanisms of adsorption and reduction reactions. In this study, periodic density functional theory (DFT) calculations were performed on the mineral goethite and its (010) surface, using the Vienna Ab Initio Simulation Package (VASP).  相似文献   

0422−476: a shell galaxy with azimuthally distributed shells     

A. Wilkinson  J.-L. Prieur  R. Lemoine  D. Carter  D. Malin  W. B. Sparks 《Monthly notices of the Royal Astronomical Society》2000,319(4):977-990

A morphological and two-colour charge-coupled device photometry study of the shell galaxy 0422−476, one of the richest known azimuthally distributed shell galaxies, is presented. Taking this galaxy as a prototype, a general method for reducing observational data of these objects is defined and quantitative parameters for use in further theoretical studies are derived.
According to some recent models (e.g. that of Thomson and Wright in 1990), the shells in such a galaxy could be density waves induced in a thick disc population of dynamically cold stars by a weak interaction with another galaxy. In 0422−476 there is no evidence of either a conventional exponential disc or a thick disc. Although it is not possible to rule out the weak interaction model, the observations continue to favour the merger model (e.g. that of Quinn from 1984).  相似文献   

Evolution of crust- and core-dominated lava flows using scaling analysis     

Angelo Castruccio  A. C. Rust  R. S. J. Sparks 《Bulletin of Volcanology》2013,75(1):1-15

The distribution of clasts deposited around a volcano during an explosive eruption typically contoured by isopleth maps provides important insights into the associated plume height, wind speed and eruptive style. Nonetheless, a wide range of strategies exists to determine the largest clasts, which can lead to very different results with obvious implications for the characterization of eruptive behaviour of active volcanoes. The IAVCEI Commission on Tephra Hazard Modelling has carried out a dedicated exercise to assess the influence of various strategies on the determination of the largest clasts. Suggestions on the selection of sampling area, collection strategy, choice of clast typologies and clast characterization (i.e. axis measurement and averaging technique) are given, mostly based on a thorough investigation of two outcrops of a Plinian tephra deposit from Cotopaxi volcano (Ecuador) located at different distances from the vent. These include: (1) sampling on a flat paleotopography far from significant slopes to minimize remobilization effects; (2) sampling on specified-horizontal-area sections (with the statistically representative sampling area depending on the outcrop grain size and lithic content); (3) clast characterization based on the geometric mean of its three orthogonal axes with the approximation of the minimum ellipsoid (lithic fragments are better than pumice clasts when present); and (4) use of the method of the 50th percentile of a sample of 20 clasts as the best way to assess the largest clasts. It is also suggested that all data collected for the construction of isopleth maps be made available to the community through the use of a standardized data collection template, to assess the applicability of the new proposed strategy on a large number of deposits and to build a large dataset for the future development and refinement of dispersal models.  相似文献   

Supermassive black hole mass measurements for NGC 1300 and 2748 based on Hubble Space Telescope emission-line gas kinematics     

J. W. Atkinson  J. L. Collett  A. Marconi  D. J. Axon  A. Alonso-Herrero  D. Batcheldor  J. J. Binney  A. Capetti  C. M. Carollo  L. Dressel  H. Ford  J. Gerssen  M. A. Hughes  D. Macchetto  W. Maciejewski  M. R. Merrifield  C. Scarlata  W. Sparks  M. Stiavelli  Z. Tsvetanov  R. P. van der Marel 《Monthly notices of the Royal Astronomical Society》2005,359(2):504-520

  相似文献   

Hornblende dehydration reactions during magma ascent at Soufrière Hills Volcano, Montserrat   总被引：1，自引：1，他引：0  

V. J. E. Buckley  R. S. J. Sparks  B. J. Wood 《Contributions to Mineralogy and Petrology》2006,151(2):121-140

Hornblende phenocrysts in recent andesites of the Soufrière Hills Volcano display reaction rims of microcrystalline plagioclase, pyroxene, Fe-oxides and interstitial glass, formed by decompression during magma ascent. Mass balance calculations give the following reactions with mineral proportions in agreement with modal abundances: These reactions require an open chemical system with exchange of selected components with surrounding melt. Volatiles, TiO₂ and alkalis are expelled and SiO₂ and FeO^T are consumed. Matrix glasses fall into two compositional groups. Glasses in pumice are relatively rich in CaO and poor in K₂O and Na₂O compared to glasses in dome samples. The former glasses formed by moderate amounts of groundmass crystallisation of plagioclase, associated with rapid magma ascent in explosive eruptions. The later glasses evolved in response to hornblende breakdown, groundmass crystallisation and mixing of melts from different levels during slow magma ascent and extended residence time in the dome. Interstitial glass compositions in reaction rims reflect the compositions of the surrounding matrix glasses, but show variable compositional differences mostly consistent with the proposed open-system reactions.  相似文献   

The ‘suitcase hypothesis’: Can entrainment of meroplankton by eddies provide a pathway for gene flow between Madagascar and KwaZulu-Natal,South Africa?     

S Ockhuis  JA Huggett  G Gouws  C Sparks 《African Journal of Marine Science》2017,39(4):435-451

Similarities in the marine fauna found off the coasts of southern Madagascar and KwaZulu-Natal Province (KZN), South Africa, led to the development of the ‘suitcase project,’ with the aim of establishing whether eddies that form off southern Madagascar may package and transport biological material across the Mozambique Channel, facilitating connectivity and gene flow. Meroplankton (larval stages of fishes and benthic invertebrates) were collected on the Madagascan shelf and along a transect through a cyclonic eddy in the Mozambique Channel. The samples were analysed using microscopy and DNA barcoding, seeking to identify species known to be common to both the southeast coast of Madagascar and the east coast of South Africa and thereby to reveal potential indicators of connectivity between these regions. The greatest zooplankton biovolume in the upper 200 m occurred on the shelf, followed by in the western part of the eddy and in the region outside the eddy to the west, and was lowest in the region outside the eddy to the east. The meroplankton were dominated by taxa of coastal origin and these were also most abundant on the shelf and in the western part of the eddy, with the lowest abundances in the region outside the eddy to the east. The findings show greater zooplankton biovolumes and larval abundances and the presence of reef-associated larval assemblages on the Madagascan shelf and along the transect through the cyclonic eddy, providing support for the suitcase hypothesis that planktonic organisms are entrained within eddies as they propagate south-westwards of the Madagascan shelf.  相似文献   

Long term exposure to respirable volcanic ash on Montserrat: a time series simulation     

T. K. Hincks  W. P. Aspinall  P. J. Baxter  A. Searl  R. S. J. Sparks  G. Woo 《Bulletin of Volcanology》2006,68(3):266-284

Frequent ash fallout from long-lived eruptions (with active phases greater than 5 years) may lead to local populations experiencing unacceptably high cumulative exposures to respirable particulate matter. Ash from Montserrat has been shown to contain significant levels of cristobalite and other reactive agents that are associated with an increased risk of developing pneumoconiosis (including silicosis) and other long-term health problems. There are a number of difficulties associated with estimating risks in populations due to uncertain and wide ranging individual exposures, change in behaviour with time and the natural variation in individual response. Present estimates of risk in workers and other population groups are simplifications based on a limited number of exposure measurements taken on Montserrat (1996–1999), and exposure−response curves from epidemiological studies of coal workers exposed to siliceous dust. In this paper we present a method for calculating the long-term cumulative exposure to cristobalite from volcanic ash by Monte Carlo simulation. Code has been written to generate synthetic time series for volcanic activity, rainfall, ash deposition and erosion to give daily ash deposit values and cristobalite fraction at a range of locations. The daily mean personal exposure for PM₁₀ and cristobalite is obtained by sampling from a probability distribution, with distribution parameters dependent on occupation, ground deposit depth and daily weather conditions. Output from multiple runs is processed to calculate the exceedance probability for cumulative exposure over a range of occupation types, locations and exposure periods. Results are interpreted in terms of current occupational standards, and epidemiological exposure−response functions for silicosis are applied to quantify the long-term health risk. Assuming continuing volcanic activity, median risk of silicosis (profusion 1/0 or higher) for an average adult after 20 years continuous exposure is estimated to be approximately 0.5% in northern Montserrat to 1.6% in Cork Hill. The occupational group with the highest exposure to ash are gardeners, with a corresponding 2% to 4% risk of silicosis. In situations where opportunities for in-depth exposure studies are limited, computer simulations provide a good indication of risk based on current expert knowledge. By running the code for a range of input scenarios, the cost-benefit of mitigation measures (such as a programme of active ash clearance) can be estimated. Results also may be used to identify situations where full exposure studies or fieldwork would be beneficial. Editorial responsibility: J Stix  相似文献   

火山岩U-Th矿物等时线年龄的新模型及其意义   总被引：1，自引：0，他引：1  

隋建立  樊祺诚  刘嘉麒  R S J Sparks 《岩石学报》2006,22(6):1511-1516

U-Th矿物等时线法定年适用于小于350ka范围的年轻火山岩。但是,火山岩矿物U-Th同位素比值不仅反映了火山的喷发年龄,而且受到岩浆房过程和结晶分异过程时间尺度的影响,在一些研究中,出现了等时线年龄(表面年龄)比实际火山喷发年龄偏老的问题,这种现象为研究岩浆房滞留时间和矿物结晶分异时间尺度问题提供了很好的条件。长期以来,国际上不乏此类研究,但迄今为止,还没有准确、实用的数值模型来描述结晶分异过程对矿物等时线年龄的影响,更无从谈起合理的计算方程。本文以一个简化的晶体生长模型(岩浆房U-Th同位素初始比值保持不变;不考虑可能的熔蚀和结晶间断;矿物的结晶速率可以简化表示,例如dV=kt·dt)为例,考察了在晶体生长(结晶分异)条件影响下的U-Th同位素衰变关系: ((~(230)Th)/(~(232)Th))=((~(230)Th)/(~(232)Th))_0·1/(λT_m)·(e~(-λ(T_1-T_m))-e~(-λT_1))+((~(238)U)/(~(232)Th))·1/(λT_m)·(e~(-λT_1)-e~(-λ(T_1-T_m)))]这仍然是一个线性方程,斜率(m)表达了火山岩喷发年龄(T_2)和矿物结晶分异时间(T_m,岩浆房滞留时问)尺度的耦合关系,而不只是喷发年龄,用方程表示为m=1/(λT_m)·(e~(-λ(T_2+T_m))-e~(-λT_2))新的模型表明,等时线出现的一般条件是不同种类的矿物具有相同的结晶历史(包括火山岩喷发年龄和矿物结晶分异的时间尺度),而不是单一的喷发年龄,在大多数年轻火山岩喷发年龄相对表较明确的条件下,我们可以应用该模型估算很多火山的岩浆房滞留时间尺度。把新的模型和方程应用于天池火山的U-Th同位素年代学研究,根据Dunlap(1996)分析测试的数据,天池火山千年大喷发岩浆房滞留时间为100ka左右。这个时间与Dunlap(1996)所估计的时间(60～100ka)的上限一致;值得注意的是,在我们的新模型中,我们认为岩浆房滞留时间和矿物结晶分异时间尺度可能被低估,实际时间应当大于等于这个数值。  相似文献