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We saw recently the Iceland volcano Eyjafjallajökull produced significant gaseous output that impacted the flight paths of several planes.

When we look at volcanic gas components, we see they produce:

  • water vapor (H2O)
  • carbon dioxide (CO2)
  • sulfur either as sulfur dioxide (SO2) (high-temperature volcanic gases) or hydrogen sulfide (H2S)
  • nitrogen
  • argon
  • helium
  • neon
  • methane
  • carbon monoxide
  • hydrogen

I'm trying to answer the question - "how many 'standard volcanic eruptions' does it take to product X moles of sulfur dioxide." Can I do it in terms of Y number of Mount St. Helens 1980 eruptions?

My question is: Is there a 'standard size' volcanic eruption in terms of gas output?

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  • $\begingroup$ As far as I know, the emission profile of each volcano is different. Therefore, it is quite difficult to model volcano emissions. Also one has to differentiate between continuous output of gases and the output at individual eruptions/events. But my knowledge is only second-hand knowledge from two colleagues who worked on measuring volcano emissions in Italy. $\endgroup$ – daniel.neumann Aug 1 '16 at 20:28
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    $\begingroup$ I think there would be a unique value for each "type" of volcano. Also, an emissions estimate would have to be in terms of activity (e.g. per total mass released), since eruptions are highly variable. Or, you could determine a ratio relative to CO2 emissions. Check out volcano.oregonstate.edu/book/export/html/151 $\endgroup$ – farrenthorpe Aug 1 '16 at 20:44
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    $\begingroup$ Even thought each volcano is different in their composition (that's why the eruptions are different as well). Maybe an indirect way to answer your question would be to analyze the amount of sulphur on the upper mantle, after all, the mantle should have statistically a similar composition compared to the erupted material of several volcanoes. According to link.springer.com/chapter/10.1007%2F978-3-642-76884-2_27 , sulphur concentration is between 300ppm and 400ppm. Therefore your job would be to analyze the size of each eruption in contrast to Mt. St. Helens. $\endgroup$ – Santiago Aug 2 '16 at 19:58
  • $\begingroup$ Thanks Santiago - can you expand that into an answer? $\endgroup$ – hawkeye Aug 2 '16 at 22:45
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There is no "standard volcano" or "standard volcanic eruption". However, to perform the calculation you want to do, you could use the "typical" of "average" volcanic eruption.

The characteristics of the "average" volcanic eruption can be found by calculating the average parameters of many volcanic eruptions. Such averages are not often reported, because the variability of volcanic eruption sizes and compositions is so large that averaging them doesn't makes much sense. But it does for your very particular application. So let's try to estimate how the "typical" volcanic eruption looks like:

Let's first figura out the typical volume of ejecta produced by a volcanic eruption: this is usually measured by the VEI (Volcanic Explosivity Index), and the formula to turn VEI into volume is

$\text{Ejecta volume}=10^{-4+\text{VEI}} \, \text{km}^3$

If we download NOAA's Significant Volcanic Eruption Database, it contains 646 recorded eruptions from 1750 to the present, and 498 of them have reported VEI values. Computing the volume ejected by each eruption (using the above formula) and taking the average we get that the "typical" eruption produces 3.2 km$^3$ of ejecta.

Using an average density of volcanic ejecta of 2 g/cm$^3$, this average volume corresponds to $6.4 \times 10^{12}$ g or 6,400,000 tons.

In typical magma, about 0.5% of its mass corresponds to gases, and for our "typical" mass that would corresponds to $3.2 \times 10^{10}$ g or 32,000 tons of gases in a "typical" volcanic eruption.

Now, about 7% of the gases corresponds to SO$_2$. That means that 0.035% of the mass of the ejecta is SO$_2$, and for our "typical" mass that would corresponds to $2.24 \times 10^9$ g or 2,240 tons of SO$_2$ in a "typical" volcanic eruption.

As you will see if you follow my references, I've pulled the above figures from multiple sources with varying degrees of reliability. Therefore, if you want a more precise estimate you can search for more accurate and updated values and repeat the exercise.

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