Is this lava you want streaming down or flowing flat like a river? I had an idea for the river like part-if it's flowing vertically I'd have to think more.

Let's say your lava section is confined to a 16x16 space equaling 256 bumps. Starting with a baseplate, add some tile pieces so that just the corners and a few middle bumps are uncovered. Now build your lava in 4 sections (1 brick high) of 4x20-varying the pattern on each block but have some colors match up. (The actual width of your lava will vary based on what studs you need open.)

You can now lay these sections down onto your smooth baseplate and move them up and down in tiny increments to simulate movement. The corners and middle bumps you left uncovered can be used to build up and over the lava for a bridge, rocks and other important set pieces you need.

If I haven't explained myself well, please PM me and I can build a small replica of what I mean for you.

This is another idea off of a MOC I just saw called "Oasis" by Nannan Z. and Tyler Clites. They used translucent 1x1 round blue plates for the water effect. Should you have enough translucent red ones, perhaps you could make something like their model. They had machines or something underneath the lego which kept them in constant motion with lights. Check it out.

Oasis

Happy building.
Jared