Throwing water into lava
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.