Possibly stopping there as they traveled between oases and pastures, they ducked into vast subterranean tunnels where molten lava had once ... in the form of rock art, lithic artefacts, stone ...

The surface of a river of lava cools and solidifies, while hot molten rock continues to flow beneath it. Eventually, lava ...

The Canary Islands not only boast the third largest volcano in the world, but also the largest natural underwater lava tunnel ... a blend of dry and submerged cave sections.