Where can one obtain a listing of the substances, and quantities of those substances, release by a volcanic eruption? Also what levels of the atmosphere (altitude) do volcanic eruptions reach?

rocky Bill

Bill - By substances I assume you mean the gases that come out of volcanoes. It is difficult to measure gas emisions during eruptions because of the danger (but remote sensing methods can determine amounts of some gases such as sulphur dioxide). Generally, volcano chemists measure gases coming from volcanoes in non-eruptive conditions. Here, for example is the gas analysis from a fumarole (a hole with gases escaping) at Vulcano volcano in the Aeolian Islands near the toe of Italy. 
	GAS		Percent
	H2O		85.6%
	CO2		11.7           Data from: D. Tedesco in 
	SO2		01.2           MONITORING ACTIVE VOLCANOES
	H2S		00.7           (edited by McGuire, Kilburn 
	HCl		00.6           and Murray); 1995, p. 318.
	H2		00.1
You can see that water vapor and carbon dioxide are most of what comes out of the fumarole. Similar results have been found for other volcanoes. But remember that the percentages of the different gases change constantly, and probably especially during eruptions when it is impossible to measure.

The height to which volcanic ejecta soars depends on the strength of the eruption. In eruptions such as occur in Hawaii, lava and gases flow easily out of the ground, and the gases don't rise more than a few thousand feet into the sky. In explosive eruptions, like that of Mt. St. Helens in 1980, gases are forcefully thrust and bouyantly rise to heights of 60,000 to 150,000 ft. These eruption clouds are threats to aircraft and place so much SO2 into the upper atmosphere that the climate becomes cooler for a few years aferwards. Winds carry such high volcanic material completely around the Earth within a few weeks.

Chuck Wood, University of North Dakota 

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