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21.
Comparison of measured far-from-equilibrium dissolution rates of natural glasses and silicate minerals at 25 °C and pH 4 reveals the systematic effects of crystallinity and elemental composition on these rates. Rates for both minerals and glasses decrease with increasing Si:O ratio, but glass dissolution rates are faster than corresponding mineral rates. The difference between glass and mineral dissolution rates increases with increasing Si:O ratio; ultra-mafic glasses (Si:O ? 0.28) dissolve at similar rates as correspondingly compositioned minerals, but Si-rich glasses such as rhyolite (Si:O ∼ 0.40) dissolve ?1.6 orders of magnitude faster than corresponding minerals. This behaviour is interpreted to stem from the effect of Si-O polymerisation on silicate dissolution rates. The rate controlling step of dissolution for silicate minerals and glasses for which Si:O > 0.28 is the breaking of Si-O bonds. Owing to rapid quenching, natural glasses will exhibit less polymerisation and less ordering of Si-O bonds than minerals, making them less resistant to dissolution. Dissolution rates summarized in this study are used to determine the Ca release rates of natural rocks at far-from-equilibrium conditions, which in turn are used to estimate their CO2 consumption capacity. Results indicate that Ca release rates for glasses are faster than those of corresponding rocks. This difference is, however, significantly less than the corresponding difference between glass and mineral bulk dissolution rates. This is due to the presence of Ca in relatively reactive minerals. In both cases, Ca release rates increase by ∼two orders of magnitude from high to low Si:O ratios (e.g., from granite to gabbro or from rhyolitic to basaltic glass), illustrating the important role of Si-poor silicates in the long-term global CO2 cycle. 相似文献
22.
Sigurdur Jakobsson 《Contributions to Mineralogy and Petrology》1997,127(1-2):129-135
The concentrations of water and carbon dissolved in an icelandite glass quenched from 1400 °C and 10 kbar were measured using
Fourier transform infra-red spectroscopy and elemental analyses of carbon and hydrogen. Only carbon dioxide and water were
observed in the fluid phase as analysed after quenching with a qudrupole mass analyser. The mole fraction of carbon dioxide
in the fluid phase ranged from 0.36 to 0.95. Carbon is dissolved as carbonate except at the highest CO2 fluid fugacity, where a small amount of molecular CO2 is observed. Dissolved carbon in the glasses, calculated as CO2, remained constant at approximately 1 wt %, in spite of the different CO2 fluid fugacities. Water was dissolved as molecular water and as hydroxyl groups, the hydroxyl concentration in the quenched
glasses remaining almost constant over the whole interval, whereas the molecular water dissolves in accordance with Henry's
law. Molecular water peaks at 5200␣cm−1 and 1630 cm−1, the hydroxyl peak at 4500␣cm−1, and the carbonate peaks at 1400 cm−1–1550 cm−1 have been calibrated using elemental analyses of C and H in the quenched glasses. As molecular water decreases in the melt
the higher wavenumber carbonate peak is observed to move towards the molecular water peak at 1630 cm−1 causing a split of the carbonate peaks, ranging from 45 cm−1 to 100 cm−1.
Received: 15 November 1995 / Accepted: 21 September 1996 相似文献
23.
The results are presented of a survey of mercury concentrations in various parts of the Icelandic environment. Values for air and gas samples include: <0.03 μg/m3 for Reykjavík, 15–20 km away from a hydrothermal area; 1–3 μg/m3 for air in a hydrothermal area near Lake Mývatn; 12–30 μg/m3 for air in Heimaey during the 1973 eruption; and 16 μg/m3 for a sample of fumarole gas. Values for fresh igneous rocks, of various compositions, extrusive (subaerial), subaqueous (up to 3000 m depth), and intrusive, range between 2 and 9 ppb. Highest values obtained for uncontaminated samples are 37 ppb for a pyrite-bearing zone in a hydrothermal drill hole, and 125 ppb for a volcanic sublimate. The sources of the mercury levels observed are briefly discussed. 相似文献
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25.
Agust Gudmundsson Niels Oskarsson Karl Gronvold Kristjan Saemundsson Oddur Sigurdsson Ragnar Stefansson Sigurdur R Gislason Pall Einarsson Bryndis Brandsdottir Gudrun Larsen Haukur Johannesson Thorvaldur Thordarson 《Bulletin of Volcanology》1992,54(3):238-246
The eruption that started in the Hekla volcano in South Iceland on 17 January 1991, and came to an end on 11 March, produced mainly andesitic lava. This lava covers 23 km2 and has an estimated volume of 0.15 km3. This is the third eruption in only 20 years, whereas the average repose period since 1104 is 55 years. Earthquakes, as well as a strain pulse recorded by borehole strainmeters, occurred less than half an hour before the start of the eruption. The initial plinian phase was very short-lived, producing a total of only 0.02 km3 of tephra. The eruption cloud attained 11.5 km in height in only 10 min, but it became detached from the volcano a few hours later. Several fissures were active during the first day of the eruption, including a part of the summit fissure. By the second day, however, the activity was already essentially limited to that segment of the principal fissure where the main crater subsequently formed. The average effusion rate during the first two days of the eruption was about 800 m3 s–1. After this peak, the effusion rate declined rapidly to 10–20 m3 s–1, then more slowly to 1 m3 s–1, and remained at 1–12 m3 s–1 until the end of the eruption. Site observations near the main crater suggest that the intensity of the volcanic tremor varied directly with the force of the eruption. A notable rise in the fluorine concentration of riverwater in the vicinity of the eruptive fissures occurred on the 5th day of the eruption, but it levelled off on the 6th day and then remained essentially constant. The volume and initial silica content of the lava and tephra, the explosivity and effusion rate during the earliest stage of the eruption, as well as the magnitude attained by the associated earthquakes, support earlier suggestions that these parameters are positively related to the length of the preceeding repose period. The chemical difference between the eruptive material of Hekla itself and the lavas erupted in its vicinity can be explained in terms of a density-stratified magma reservoir located at the bottom of the crust. We propose that the shape of this reservoir, its location at the west margin of a propagating rift, and its association with a crustal weakness, all contribute to the high eruption frequency of Hekla. 相似文献
26.
Paul F. McMillan Sigurdur Jakobsson John R. Holloway Lynn A. Silver 《Geochimica et cosmochimica acta》1983,47(11):1937-1943
The Raman spectra of albite glasses with 4.5 and 6.6 weight percent water have been obtained, and are compared with that of a dry sample. The hydrous glasses show bands near 3600 cm?1 due to O-H stretching, and a previously unreported weak band near 1600 cm?1 due to bending of molecular H2O. Other weak spectral features are discussed, and the effect of dissolved water on the aluminosilicate framework vibrations is considered. 相似文献
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28.
Dr. Sigurdur Thorarinsson 《International Journal of Earth Sciences》1968,57(3):705-718
The rate of the lava production of three Icelandic fissure eruptions (Lakagigar 1783, Hekla 1947, Askja 1961) is calculated and an attempt is made at a reasonable approximation of the rate of lava production per length and width of the feeding fissures and the rate of upward migration of the magma through the fissures. The results are summed up in Table 2. The figures for the maximum upward migration there presented should be regarded as minimum figures. As a comparison with the mainly lava producing fissure eruptions the tephra production of the acid and highly explosive Askja eruption of 1875 is discussed. It has hitherto been assumed that the enormous amount of tephra, about 2 km3, which was produced by this eruption in 8 1/2 hours, came entirely from the Viti crater, but with regard to its small diameter it seems likely that the very fine grained tephra produced during the first hours of the eruption was partly expelled from nearby fissures now covered by Lake Öskjuvatn.
Dedicated to Professor Dr. A.Rittmann on the occasion of his 75. birthday 相似文献
Zusammenfassung Die Rate der Lavaförderung bei drei isländischen Spalteneruptionen (Lakagigar 1783, Hekla 1947, Askja 1961) wird errechnet, und es wird versucht, einen Annäherungswert zu gewinnen über die Rate der Lavaförderung, bezogen auf Länge und Weite der Zuführungsspalten und die Rate der Aufwärtsbewegung des Magma durch die Spalten. Die Ergebnisse sind in Tafel 2 zusammengefaßt. Die darin angegebenen Zahlen für die maximale Aufwärtsbewegung sollten als Minimum aufgefaßt werden. Als Vergleich mit den hauptsächlich Lava führenden Spalteneruptionen wird die Tephraproduktion der sauren und hochexplosiven Askja Eruption von 1875 behandelt. Bisher wurde angenommen, daß die enorme Menge Tephra — ungefähr 2 km3, die diese Eruption in 8 1/2 Stunden hervorbrachte — ausschließlich aus dem Viti Krater kam; aber in Anbetracht seines geringen Durchmessers scheint es wahrscheinlich, daß die sehr feinkörnige Tephra, die während der ersten Stunden der Eruption entstand, teilweise von nahegelegenen Spalten ausgeworfen wurde, die jetzt vom Öskjuvatn-See bedeckt sind.
Résumé La mesure de production de lave de trois éruptions fissurales de l'Islande (Lakagigar 1783, Hekla 1947, Askja 1961) est calculée et il est essayé de rapprocher la mesure de cette production à l'égard de longueur et largeur des fissures d'alimentation, et la mesure de la migration vers le haut du magma par les fissures. Les résultats sont présentés au tableau 2. Les chiffres de la migration maximum vers le haut doivent être entendus comme minimum. En comparaison avec l'éruption fissurale produisant principalement de la lave, la téphra production de l'acide et fort explosive éruption de l'Askja de 1875 est discutée. On a supposé jusqu'à présent que l'énorme masse de téphra, environ 2 km3, qui fut produite lors de cette éruption en 8 1/2 heures, provenait seulement du cratére Viti; mais considérant son petit diamètre il est probable que la téphra de grain fin fut en partie lancée par des fissures voisines et qui à présent sont couvertes par le Lac Öskjuvatn.
(Lakagígar 1783; Hekla 1947; Askja 1961). . Askja 1875 , . .
Dedicated to Professor Dr. A.Rittmann on the occasion of his 75. birthday 相似文献
29.
Until two decades or so ago the petrography of Iceland seemed to present a rather simple picture. About 99 per cent of the rocks were regarded as basaltic, 1 per cent as rhyolitic and rocks of intermediate composition as nearly non-existent. Recent research has changed this picture. Central volcanoes producing acid and intermediate lava and tephra have played a considerable role both in the Tertiary and Quaternary. Contrary to the lava massproducing basalt volcanoes, fed by a deep-seated and rather uniform basalt magma source, the differentiated central volcanoes are normally fed by separated magma chambers at smaller depth, where differentiation takes place between the eruptions, resulting in intermediate and acid products which bridge the immiscibility gap between the basalts and the rhyolites. Eight to ten per cent of the postglacial lavas and tephras and about 25 per cent of the historical ones are acid or intermediate.Opinions still differ as to whether the existence of these rocks can be explained solely as the result of gravitational differentiation of parent basalt magma or has to be explained partly by a remelting of a continental layer beneath the plateau-basalts. There are, however, some rather strong geological evidences in favour of the existence of such a layer and they seem at the moment not to be contradicted by geophysical research.The Surtsey eruption has demonstrated the close relation between the craterrows, shieldvolcanoes and tablemountains and convincingly shown how greatly external circumstances may influence volcanic activity and the shape of a volcano. The eruption focused interest on the neovolcanic zone of Iceland as a supra marine part of the Mid-Atlantic rift-ridge zone, where volcanic activity has taken place under similar conditions as along its submarine parts, viz. under water (glacial meltwater) when the Pleistocene ice-sheets blanketed the volcanic activity. Similar morphological types of volcanoes can therefore be expected in both cases, viz. steepsided mounds and long steepsided ridges.
Zusammenfassung Bis vor ungefähr zwei Jahrzehnten schien die Petrographie Islands ein verhältnismäßig einfaches Bild zu bieten. Etwa 99% des Gesteins wurde für basaltisch, 1% für rhyolithisch, und Gesteine von intermediärer Zusammensetzung für fast nicht existent gehalten. Die jüngste Forschung hat dieses Bild gewandelt. Zentralvulkane, die saure und intermediäre Lava und Tephra ausstoßen, haben im Tertiär wie auch im Quartär eine erhebliche Rolle gespielt. Im Gegensatz zu den Basaltvulkanen, welche von einer tiefgelegenen und ziemlich einheitlichen Basaltmagmaquelle gespeist werden und Lava in Massen ausstoßen, werden die differenzierten Zentralvulkane normalerweise von getrennten Magmakammern in geringerer Tiefe gespeist, wo eine Differentiation zwischen den Eruptionen stattfindet. Es entstehen intermediäre und saure Materialien, die die Immiszibilitätslücke zwischen den Basalten und den Rhyolithen überbrücken. 8–10% der postglazialen Laven und Tephren und etwa 25% der historischen sind sauer oder intermediär.Die Meinungen gehen noch auseinander hinsichtlich der Frage, ob das Vorkommen dieses Gesteins allein als das Ergebnis einer gravitativen Differentiation des basaltischen Stamm-Magmas erklärt werden kann, oder ob man es teilweise mit einem Wiedereinschmelzen einer Sialschicht unterhalb der Tafelbasalte erklären muß. Es gibt für die Existenz einer solchen Schicht einige ziemlich überzeugende geologische Zeugnisse, und es scheint so, als ob diesen gegenwärtig durch die geophysikalische Forschung nicht widersprochen würde.Die Surtsey-Eruption hat die enge Beziehung zwischen den Kraterreihen, den Schildvulkanen und den Tafelbergen aufgezeigt und überzeugend dargelegt, wie stark äußere Umstände die Vulkantätigkeit und die Form eines Vulkans beeinflussen können. Diese Eruption konzentrierte das Interesse auf die neovulkanische Zone Islands als eines supramarinen Teils des mittelatlantischen Rückens, wo die Vulkantätigkeit während der Glazialperioden der quartären Eiszeit unter ähnlichen Bedingungen stattgefunden hat, wie entlang ihrer submarinen Teile, d. h. unter Wasser (glazialem Schmelzwasser). Man darf deshalb in beiden Fällen ähnliche morphologische Vulkantypen erwarten, d. h. steilwandige Hügel und lange steilwandige Rücken.
Résumé Vingt ans plus tôt la pétrographie de l'Islande paraissaît assez simple. Les recherches récentes ont changé cette conception. Des volcans centraux ont joué un rôle considérable au Tertiaire et au Quaternaire. Les volcans basaltiques sont nourris par des sources profondes et assez homogénes de magma basaltique. Par contre les volcans centraux sont nourris par des chambres magmatiques moins profondes ou il y a une différenciation des éruptions: il y a des matériaux intermédiaires et acides. 8–10% des laves et tephras postglaciales et 25% des laves et tephras historiques sont acides ou intermédiaires.Les opinions diffèrent encore dans la question si l'existence de ces roches est le résultat d'une différenciation du magma basaltique original ou s'il s'agit d'une refonte d'une couche continentale au-dessous des plateaux basaltiques.L'éruption de Surtsey a démontré la relation étroite entre les chaînes de cratères, les volcans en bouclier et les guyots. Elle montre combien des circonstances extérieures ont influencé l'activité volcanique et la forme d'un volcan Cette éruption attircut l'intérêt vers la zone néo volcanique de l'Islande. C'est la partie supramarine de la faille-dorsale-zone mi-atlantique ou l'activité volcanique a en lieu sous des conditions pareilles à celles de la partie submarine, c'est à dire sous l'eau (eau glaciale). Dans les deux cas on pent supposer de pareils types morphologiques de volcans.
. , 99% 1% . , , . . . .相似文献
30.
Birgir Hrafnkelsson Kristinn M. Ingimarsson Sigurdur M. Gardarsson Arni Snorrason 《Stochastic Environmental Research and Risk Assessment (SERRA)》2012,26(1):1-20
River discharges are traditionally modeled by employing a standard power-law methodology. Recently, the Bayesian approached
has successfully been applied to improve the estimates of the standard power-law. In this article, an extension to the standard
power-law based on Bayesian B-splines is developed and tested on data sets from 61 different rivers. The extended model is
evaluated against the standard power-law using two measures, the Deviance Information Criterion and Bayes factor. The extended
model captures deviations in the data from the standard power-law but reduces to the standard power-law when that model is
adequate. The standard power-law is inadequate for 26% of the rivers while the extended model provides an adequate fit in
all of those cases and for the remaining 74% of the rivers the extended model and the power-law model both give adequate fit
with almost identical estimates. 相似文献