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  • 1
    Electronic Resource
    Electronic Resource
    Physical properties of the 1980 Mount St. Helens cryptodome magma (1997)
    Springer
    Bulletin of volcanology 59 (1997), S. 103-111 
    Details
    ISSN: 1432-0819
    Keywords: Key words Magma ; Mount St. Helens ; Cryptodome ; Viscosity ; Physical ; Rheological ; Experimental
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  Physical properties of cryptodome and remelted samples of the Mount St. Helens grey dacite have been measured in the laboratory. The viscosity of cryptodome dacite measured by parallel–plate viscometry ranges from 10.82 to 9.94 log10 η (Pa s) (T=900–982  °C), and shrinkage effects were dilatometrically observed at T〉900  °C. The viscosity of remelted dacite samples measured by the micropenetration method is 10.60–9.25 log10 η (Pa s) (T=736–802  °C) and viscosities measured by rotational viscometry are 3.22–1.66 log10 η (Pa s) (T=1298–1594  °C). Comparison of the measured viscosity of cryptodome dacitic samples with the calculated viscosity of corresponding water-bearing melt demonstrates significant deviations between measured and calculated values. This difference reflects a combination of the effect of crystals and vesicles on the viscosity of dacite as well as the insufficient experimental basis for the calculation of crystal-bearing vesicular melt viscosities at low temperature. Assuming that the cryptodome magma of the 18 May 1980 Mount St. Helens eruption was residing at 900  °C with a phenocryst content of 30 vol.%, a vesicularity of 36 vol.% and a bulk water content of 0.6 wt.%, we estimate the magma viscosity to be 1010.8 Pa s.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004450050178
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  • 2
    Electronic Resource
    Electronic Resource
    The effect of water on the viscosity of a haplogranitic melt under P-T-X conditions relevant to silicic volcanism (1996)
    Springer
    Contributions to mineralogy and petrology 124 (1996), S. 19-28 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  The viscosities of hydrous haplogranitic melts synthesized by hydrothermal fusion at 2 kbar pressure and 800 to 1040° C have been measured at temperatures just above the glass transition and at a pressure of 1 bar using micropenetration techniques. The micropenetration viscometry has been performed in the viscosity range of 109 Pa s to 1012 Pa s. The samples ranged in water content from 0.4 to 3.5 wt%. For samples with up to 2.5 wt% H2O, the water contents have been determined using infrared spectroscopy obtained before and after each viscometry experiment to be constant over the duration of the measurements. Above this water content a measurable loss of water occurs during the viscometry. The viscosity data illustrate an extremely nonlinear decrease in viscosity with added water. The viscosity drops drastically with the addition of 0.5 wt% of water and then shallows out at water contents of 2 wt%. An additional viscosity datum point obtained from the analysis of fluid inclusions in a water-saturated HPG8 confirms a near invariance of the viscosity with the addition of water between 2 and 6 wt%. These measurements may be compared directly with the data of Hess et al. (1995, in press) for the effects of excess alkali and alkaline earth oxides on the viscosity of HPG8 (also obtained at 1 bar). The viscosity of the melts, compared on an equivalent molar basis, increases in the order H2O〈(Li2O〈Na2O〈 K2O〈Rb2O,Cs2O〈BaO〈SrO〈CaO〈MgO〈 BeO). The extraordinary decrease in melt viscosity with added water is poorly reproduced by the calculation scheme of Shaw (1972) for the range of water contents investigated here. The speciation of water in the quenched glasses can be used to quantify the dependence of the viscosity on hydroxyl content. Considering only the hydroxyl groups as active fluidizers in the hydrous melts the nonlinearity of the viscosity decrease and the difference with the effects of the alkali oxides becomes larger. Consequences for degassing calcalkaline rhyolite are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004100050170
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    Paper (German National Licenses)
    Fulltext
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