Tittle should say all, but I will explain how I did that.
First of all, it display a small animation (about 5-6 frames). I think that It's the first, because I don't saw it anywhere until I made it.
So, when you press the button it actives some pistons and the system automatically retract these pistons after a delay. When all pistons are retracted, the lava flow is making the animation.
Watch the video to see better.
It's just a prototype.
If you want to experiment with it, fell free to download the world from video's description or from World save link on the right.