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101.
102.
Lucia Gurioli Bruce F. Houghton Katherine V. Cashman Raffaello Cioni 《Bulletin of Volcanology》2005,67(2):144-159
The 79 AD eruption of Vesuvius included 8 eruption units (EU1–8) and several complex transitions in eruptive style. This study focuses on two important transitions: (1) the abrupt change from white to gray pumice during the Plinian phase of the eruption (EU2 to EU3) and (2) the shift from sustained Plinian activity to the onset of caldera collapse (EU3 to EU4). Quantification of the textural features within individual pumice clasts reveals important changes in both the vesicles and groundmass crystals across each transition boundary. Clasts from the white Plinian fall deposit (EU2) present a simple story of decompression-driven crystallization followed by continuous bubble nucleation, growth and coalescence in the eruptive conduit. In contrast, pumices from the overlying gray Plinian fall deposit (EU3) are heterogeneous and show a wide range in both bubble and crystal textures. Extensive bubble growth, coalescence, and the onset of bubble collapse in pumices at the base of EU3 suggest that the early EU3 magma experienced protracted vesiculation that began during eruption of the EU2 phase and was modified by the physical effects of syn-eruptive mingling-mixing. Pumice clasts from higher in EU3 show higher bubble and crystal number densities and less evidence of bubble collapse, textural features that are interpreted to reflect more thorough mixing of two magmas by this stage of the eruption, with consequent increases in both vesiculation and crystallization. Pumice clasts from a short-lived, high column at the onset of caldera collapse (EU4) continue the trend of increasing crystallization (enhanced by mixing) but, unexpectedly, the melt in these clasts is more vesicular than in EU3 and, in the extreme, can be classified as reticulite. We suggest that the high melt vesicularity of EU4 reflects strong decompression following the partial collapse of the magma chamber.Editorial responsibility: D.B. Dingwell 相似文献
103.
Petrogenesis of Mafic Inclusions in Rhyolitic Lavas from Narugo Volcano, Northeastern Japan 总被引:1,自引:0,他引:1
Mafic inclusions present in the rhyolitic lavas of Narugo volcano,Japan, are vesiculated andesites with diktytaxitic texturesmainly composed of quenched acicular plagioclase, pyroxenes,and interstitial glass. When the mafic magma was incorporatedinto the silica-rich host magma, the cores of pyroxenes andplagioclase began to crystallize (>1000°C) in a boundarylayer between the mafic and felsic magmas. Phenocryst rim compositionsand interstitial glass compositions (average 78 wt % SiO2) inthe mafic inclusions are the same as those of the phenocrystsand groundmass glass in the host rhyolite. This suggests thatthe host felsic melt infiltrated into the incompletely solidifiedmafic inclusion, and that the interstitial melt compositionin the inclusions became close to that of the host melt (c.850°C). Infiltration was enhanced by the vesiculation ofthe mafic magma. Finally, hybridized and density-reduced portionsof the mafic magma floated up from the boundary layer into thehost rhyolite. We conclude that the ascent of mafic magma triggeredthe eruption of the host rhyolitic magma. KEY WORDS: mafic inclusion; stratified magma chamber; magma mixing; mingling; Narugo volcano; Japan 相似文献
104.
105.
Laboratory studies examined two key aspects of the performance of a continuous-flow diffusion chamber (CFD) instrument that detects ice nuclei (IN) concentrations in air samples: separating IN from non-IN, and collecting IN aerosols to determine chemical composition. In the first study, submicron AgI IN particles were mixed in a sample stream with submicron non-IN salt particles, and the sample stream was processed in the CFD at −19°C and 23% supersaturation with respect to ice. Examination of the residual particles from crystals nucleated in the CFD confirmed that only AgI particles served as IN in the mixed stream. The second study applied this technique to separate and analyze IN and non-IN particles in a natural air sample. Energy-dispersive X-ray analyses (EDS) of the elemental composition of selected particles from the IN and non-IN fractions in ambient air showed chemical differences: Si and Ca were present in both, but S, Fe and K were also detected in the non-IN fraction. 相似文献
106.
银山地区火山岩-次火山岩由流纹岩、流纹英安斑岩、英安质熔岩、英安斑岩和粗面安山斑岩组成,喷发和侵入存在着反序特征.通过各种物理化学方法确定了岩浆房中存在的化学成分和温度、密度、粘度梯度.建立了以英安质岩浆为主,顶部有一层富SiO2、富K的流纹质岩浆,底部为少量粗面安山质岩浆的带状岩浆房.岩浆演化及带状岩浆房的形成是分离结晶、同化混染、岩浆对流和边界层机制共同作用的结果. 相似文献
107.
长白山天池火山研究进展 总被引:25,自引:0,他引:25
长白山天池火山距今4105年以来至少发生过两次大规模喷发。其最近的一次大喷发发生于公元850~1040年间。估计了这次喷发的喷发物体积和C1,F,S等的释放量。数值模拟表明,该次大喷发对全球气候变化产生过重要影响,最近的地球物理探测结果显示,在该火山下面存在地壳和上地幔双层岩浆房。认为该火山现在仍是一座具潜在灾害性大喷发危险的现代活动火山。 相似文献
108.
在过去的20年里,探测和勾画岩浆囊的科学有了长足的进步。多种地震技术,包括速度和衰减的层析成像,地震活动性映像,反射和折射,势场技术,如重力,大地测量和电磁观测,都提供了关于在几个火山下面的岩浆囊的大小,形状和物理状态的有用信息。本文对这些技术进行了讨论和综述。我国已在P波波速层析成像方面开展了一系列工作。特别是在云南地区已得到了该省及其邻近地区的三维速度图像。由于现有台网不够密集,获得的速度图像分辨较低。尽管如此,在腾冲地区从20km到450km深度都有低速度结构的显示。要想系统地研究腾冲火山地区的火山构造和地震活动性,以及探测该地区的岩浆囊,必须在该地区布设较密集的地震观测台网。 相似文献
109.
The design and performance of a smog chamber for the study of photochemical reactions under simulated environmental conditions is described. The chamber is thermostated for aerosol experiments, and it comprises a gas chromatographic sample enrichment system suitable for monitoring hydrocarbons at the ppbv level. By irradiating NO
x
/alkane-mixtures rate constants for the reaction of OH radicals with n-alkanes are determined from n-pentane to n-hexadecane to be (k±2)/10–12 cm3 s–1=4.29±0.16, 6.2±0.6, 7.52 (reference value), 8.8±0.3, 10.2±0.3, 11.7±0.4, 13.7±0.3, 15.1±0.5, 17.5±0.6, 19.3±0.7, 22.3±1.0, and 25.0±1.3, respectively at 312 K. Rate constants, (k±2)/10–17 cm3 s–1, for the reaction of ozone with trans-2-butene (21.2±1.0), cis-3-methylpentene-(2) (47.2±1.7), cyclopentene (62.4±3.5), cyclohexene (7.8±0.5), cycloheptene (28.3±1.5), -pinene (8.6±1.3), and -pinene (1.4±0.2) are determined in the dark at 297 K using cis-2-butene (13.0) as reference standard. 相似文献
110.
Laboratory studies of some environmental variables controlling sulfur emissions from plants 总被引:8,自引:0,他引:8
R. Fall D. L. Albritton F. C. Fehsenfeld W. C. Kuster P. D. Goldan 《Journal of Atmospheric Chemistry》1988,6(4):341-362
Several trace sulfur gases that can have a significant influence on atmospheric chemistry are emitted from biological systems. In order to begin to address biological questions on the mechnisms of production of such gases, laboratory-scale experiments have been developed that reproduce such emissions under controlled conditions. Using a flux chamber technique, flats containing soil, or soil plus plants were sampled for the net fluxes of sulfur gases. The major sulfur gas emitted from all the plants tested (corn, alfalfa, and wheat) was dimethyl sulfide (DMS). Alfalfa and wheat also emitted lesser amounts of methanethiol, variable amounls of hydrogen sulfide, and in some experiments wheat emitted carbon disulfide. The use of a plant incubator allowed a systematic study of the effects of variables such as temperature, photon flux, and carbon dioxide levels, on these emissions. Fluxes of all the emitted sulfur gases increased exponentially with increasing air temperature, and increased with increasing photon flux up to a saturation level of \~300 E/m–2 sec-1. Three to four-fold changes in DMS flux were observed during light to dark or dark to light transitions. By varying the CO2 content of the chamber flush gas, it was shown that the observed sulfur fluxes from corn and alfalfa were not related to the CO2 concentration. Growing these crop plants through holes in a Teflon soil-covering film allowed a separate determination of soil and foliage emissions and substantiation of the light dependent uptake of COS by growing vegetation observed in previous field studies. 相似文献