image creditLava tubes are natural conduits through which lava travels beneath the surface of a lava flow. Typically they are expelled by a volcano during an eruption and can be actively draining lava from a source; or they can be extinct, meaning the lava flow has ceased and the rock has cooled and left a long, cave-like channel.
Here is a gallery of beautiful lava tubes around the world along with some interesting images of various formations within lava tubes such as lavacicles and lava pillars. When viewing, try to imagine a time when lava was flowing through these remarkable tubes.
