Houdini: Making objects appear and then gradually lengthen (preliminary)

For Cenote, I am working on magic lights creeping up from the lake to the temple. 

This involved a boolean and a lot of grids. I'm too tired right now to really illustrate my process so I'm just going to drop in a few screenshots. 

Here is my node network. The leftmost row is an animated box that I am using to create a boolean to make the magic light lines appear. The rest of them are the light lines themselves. 

This is all inside of the geometry node representing a box. The boolean used is an intersect. 

Wireframe preview -- these obviously look super ghetto; I was just trying to get it working first and foremost. So there's virtually zero art direction and the shapes are pretty crappy. And it's not in the shot yet. 

Quick screenshot of the concept art (not mine): 

This is obviously just the lines right now. I will either make spheres or particles to represent the stuff bubbling out of the lake. 

And finally, here is the animation itself. Again, it's not fantastic, but it doesn't need to be. I just wanted to make sure I could get everything working programmatically. The next step will be to art direct it, and put the same version of it into the shot. Right now, it's just a proof of concept. :)