Chunks are 32x32x32 and are unloaded once you are more than 2 chunks away from it. There is a separate type of 512x512x512 chunk for structures that does not get unloaded right now, but it would take forever for this to fill up your memory (they don't even take up a megabyte) so I left it as it for the demo. Chunk unloading was rushed for the demo and causes rare crashes, but the entire browser crashing is a little weird. You can tell that chunks get unloaded by destroying stuff, moving past a few chunks, then turning back. The blocks will all be replaced because nothing is saved to disk currently.