Stilly, I think your ten-yard dumpster is a good measure of volume. People are familiar with it.
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One day when we were on Stromboli, the volcano was sending a murky gray cloud right into the town. We went into a pizza restaurant, and thought to myself, "This table still has crumbs on it." But on closer examination, the crumbs were tiny bits of lava from out of the cloud. I photographed them.

I suppose, though, that it's the gases from the cloud (including H2S) that are bad for the lungs. The same thing applies in Iceland.