I’ve been writing about an in-browser voxel game project of mine over at voxeling.tumblr.com. The game – if it can actually be called that (probably not) – is built on a JavaScript game engine for building minecraft-like environments. If you want to try it out, contact me.
The following screenshot shows a lava flow created in-game using lava and obsidian textures. Credit for the textures and lava flow goes to phionabrie. (fullsize): 
The whole thing is still pretty fledgeling, but I’m having a blast building out functionality and optimizing the engine and networking components.
Take care!