Archaeologists have found evidence of human habitation within lava tubes for the first time, in the deserts of northern Saudi Arabia.

Lava tubes are caves that form during a volcanic eruption. The surface of a river of lava cools and solidifies, while hot molten rock continues to flow beneath it. Eventually, lava drains out of the tube, leaving behind a tunnel.

Mathew Stewart at Griffith University in Brisbane, Australia, and his colleagues excavated a trench inside Umm Jirsan. At 1.5 kilometres in length, it is the biggest lava tube in Saudi Arabia. The…