I was a little disappointed when I let some thermite melt and hit ice and saw no explosion Not sure if it's even possible to do so as melted is lava, but it would be really cool if thermite reacted with ice the same way it does in real life for example, when the thermite hits the ice it would create a lot of pressure really fast, or something like that :P
I saw it on mythbusters too... It happened when it was ignited though. Several theories I've seen presented are 1)The intense heat from the thermite released so much steam that the rapid expansion of gases propelled the remaining ice chunks great distances 2)The reaction seperated the hydrogen and oxygen from the water and cause an intense explosion from the two gases. 3)A combination of the two above.
Therefore, if we could incorporate a reaction which either causes steam to be produced at a rate which turned the ice into snow from the pressure or produce oxygen and hydrogen and ignited it.