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While discussing magma in class with my students, I showed a video of a man throwing water onto molten, running lava. A large flame ensued. I realize that the water is being converted into steam and expanding extremely rapidly, but why does this create a small "explosion," if you will?

Surely none of the lava is being "atomized" into the air in small droplets, is it? But even so, they would not light aflame.

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  • $\begingroup$ youtube.com/watch?v=0XgpYXVN-Kk $\endgroup$ – Nilay Ghosh Jan 25 '17 at 3:47
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    $\begingroup$ Are you certain it was a flame and not just lava bubbles with thin enough walls that it appeared more orange than red, thus giving the illusion of a flame? $\endgroup$ – airhuff Jan 25 '17 at 4:22
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    $\begingroup$ I think linking the video you are referring to would be potentially helpful in answering this question. $\endgroup$ – ringo Jan 25 '17 at 4:45
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    $\begingroup$ The first thing I think of, is this. $\endgroup$ – Nij Jan 25 '17 at 8:22
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    $\begingroup$ The liquid looks like it is in a water bottle, but is it water? From that amount of liquid and flame I'd suspect alcohol or gasoline. The numb-numb was putting on a show not a science demonstration. $\endgroup$ – MaxW Jan 25 '17 at 17:29
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This is a Steam explosion generally the flame is due to the hydrogen produced when water is superheated so thermal decomposed into $\ce{H2}$ and $\ce{O2}$.

Quoting wikipedia:

Steam explosions are not normally chemical explosions, although a number of substances react chemically with steam (for example, zirconium and superheated graphite react with steam and air respectively to give off hydrogen, which burns violently in air) so that chemical explosions and fires may follow.

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    $\begingroup$ Theory: Is the lava hot enough to decompose some of the water into hydrogen and oxygen gas, thus making way for a hydrogen explosion, which releases a lot of energy, which is absorbed by other waters, which decomposes more of them? It seems like good potential for a chain reaction. $\endgroup$ – Jesuspowder Jan 26 '17 at 16:48

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