Lava and magma waterfalls are waterfall-like cascades of either lava (if it is above ground) or magma (if it is below ground). They are often found in volcanic areas or deep underground. They may be a portion of a lava river, or feed into a lava lake. In fantasy worldbuilding they may exist in lavalands or in evil realms.

“Waterfall” is a bit of a misnomer, isn’t it?