Volcanic Effects

Volcanic aerosols (mostly sulfate) have been suggested to have global effects on the climate when ejected in sufficient amounts into 

FIGURE 4 Observed MSU temperature, shown as dashed line, for channel 4 (top) for the period 1979-1997 and the equivalent for the simulations with Mt. Pinatubo and stratospheric ozone. The mean value obtained from the six realizations is denoted by the solid line, whereas the shaded area represents this value plus and minus one standard deviation of the individual simulations, respectively. The same for channel 2LT (bottom). Note the steady response in the stratosphere and the large variability in the lower troposphere, (from Bengtsson et al, 1999). 

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Unless explosive emptions occur closely together in time, the effects of one emption will have dissipated by the time the next occurs. Volcanic effects therefore occur on high-frequency (interannual) time scales, while solar output changes occur on decade-to-century time scales. Climate is also influenced internally by changes within the ocean (strengths and directions of currents, rates of up-welling, and deepwater formation). 

Similar heterogeneous reactions also can occur, but somewhat less efticientiy, in the lower stratosphere on global sulfate clouds (ie, aerosols of sulfuric acid), which are formed by oxidation of SO2 and COS from volcanic and biological activity, respectively (80). The effect is most pronounced in the colder regions of the stratosphere at high latitudes. Indeed, the sulfate aerosols resulting from emptions of El Chicon in 1982 and Mt. Pinatubo in 1991 have been impHcated in subsequent reduced ozone concentrations (85). 

Seismic effects and earthquake engineering is covered in this part to study the behaviour of an object under seismic conditions and its suitability for critical installations. The formation of the earth and movements of tectonic plates that cause earthquakes and volcanic eruptions are described,... 

The movement of Earth s crustal plates and the continents they contain - continental drift -has had enormous effects on climate, sea levels, and the distributions of organisms. Mass extinctions of organisms have usually accompanied major drops in sea levels. The collision of all the continents to form the gigantic landmass called Pangaea about 260 million years ago, triggered massive volcanic eruptions. The volcanoes... 

Volcanic activity has a significant effect on the mobilization of metals, particularly the more volatile ones, e.g., Pb, Cd, As, and FFg. Effects of volcanism are qualitatively different from those of the weathering and other near-surface mobilization processes mentioned above, in that volcanism transports materials from much deeper in the crust and may inject elements into the atmospheric reservoir. 

Hydrogen sulphide occurs naturally, e.g. in natural gas and petroleum, volcanic gases, and from decaying organic matter. It may be present near oil wells and where petroleum is processed. Commercially it is obtained as a by-product from many chemical reactions including off-gas in the production of some synthetic polymers (e.g. rayon, nylon) from petroleum products, and by the action of dilute mineral acids on metal sulphides. Physical properties are summarized in Table 9.14 and effects of temperature on vapour pressure are shown in Figure 9.5. 

They calculated the change in 8 0 values of hydrothermally altered volcanic rocks as a function of water to rock ratio by weight and temperature, assuming that oxygen isotopic equilibrium is attained in a closed system, and demonstrated that the increase in 8 0 values of altered andesitic rocks from the veins towards peripheral zones can be interpreted as a decrease in temperature from the vein system (Fig. 1.135). In their calculations, the effect of mixing of hydrothermal solution with groundwater was not considered. 

In addition to hydrothermal and volcanic activity, metamorphism may have influenced the CO2 levels of the atmosphere and caused climate changes. Based on a model of the Cenozoic extension in the North American Cordillera, Nesbitt et al. (1995) demonstrated that CO2 generation associated with crustal extension may have been a major contributor to the elevated CO2 levels of the Cenozoic atmosphere and the resulting global warming due to the CO2 greenhouse effect. 

Schmidt et al. (1999) report Dpb of 0.034-0.045 for two experiments with leucite lamproite melt composition for a basanitic melt composition La Tourrette et al. (1995) give Z)pb = 0.10. In all three cases Z)pb consistently falls below, by a factor of 3, the parabola defined by the other 2+ cations, as previously noted for several other minerals. Here the implication is that the effective Xll-fold ionic radius of Pb is slightly smaller than the value given in Table 2, i.e., closer in size to rsr. Upb/Usr is between 0.6 and 1.2, in these experiments. In the PIXE partition study of Ewart and Griffin (1994) for acid volcanic rocks, Z)pb ranges from 0.21 to 2.1 (3 samples), with Upb/Usr of 0.29 to 2.9. Until there are further experimental determinations of Upb, or better constraints on its ionic radius, we suggest that Z)pb = E>sr-... 

Could lightning flashes occurring during volcanic eruptions have been effective energy sources for prebiotic syntheses An answer to this question would require not only reliable information on the exact chemical composition of the exhalation... 

There is no doubt that volcanic activity had various effects on the chemical processes occurring on the young Earth. Two articles deal with simulation experiments intended to study how volcanic exhalations may have affected prebiotic chemistry. 

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