what is lava when it hardens
Noun. 1. lava-rock that in its molten form (as magma) issues from volcanos; lava is what magma is called when it reaches the surface. aa-a dry form of lava resembling clinkers. pahoehoe-freely flowing lava. pillow lava-lava that hardened in rounded shapes suggestive of pillows; believed to result from underwater eruptions.