Minecraft wiki entry for Lava, associated text: In the Nether, lava is more common than water in the Overworld. Seas of lava occur, with sea level at y-level 32, about a quarter of the total height of the Nether (as the usable space in the Nether is 128 blocks tall). They can extend down to about y-level 19-22. Lava also randomly appears in single blocks inside netherrack formations. Lava is also generated as a single source in well rooms in nether fortresses. There are also large pockets of lava generated under y-19 and can reach all the way down to bedrock level. These pockets are generally over 12 blocks in height and often connect to a large lava lake on y-32; the size of these pockets in 1.18 can range from the size of a singular pre-1.18 ravine to multiple ravines combined.