A cave formed by flowing lava and often found in volcanic regions is a lava tube.
Lava tubes develop during eruptions, especially when low-viscosity basaltic lava flows steadily from a volcanic vent. The edges and surface of the flow cool and harden first, creating walls and a roof over the still-molten lava beneath. When the eruption ends or the lava is diverted, the molten interior may drain away and leave a hollow passage.
These caves are therefore volcanic in origin, unlike solution caves, which form when groundwater dissolves limestone or other soluble rock. Glacier caves are carved by meltwater within or beneath ice, while sea caves are typically eroded by waves along coastlines. Lava tubes can contain distinctive features such as lavacicles, lava benches, flow lines, and hardened lava coatings.
Lava tubes occur on volcanoes and volcanic islands worldwide. Kazumura Cave in Hawaii is recognized as the world's most extensive known lava tube, while Manjanggul Cave on Jeju Island is a well-known tourist example.