Minecraft wiki entry for Time-saving_tips, associated text: Once you have collected (or blocked off) a lava source block, it can take a very long time for the flowing lava to disappear. Using cheap blocks: dirt, cobblestone, flammable leaves or netherrack to mop up the remainder saves waiting for it to disappear naturally. Even one block replacing the highest level of the flow will make the rest vanish much more quickly. You can also use torches to clean up lingering lava.