Lava Tube - John Seach

Lava tubes are natural conduits through which lava travels beneath the surface of a lava flow.
Tubes form by the crusting over of lava channels and pahoehoe flows.
When the supply of lava stops at the end of an eruption or lava is diverted elsewhere,
lava in the tube system drains downslope and leaves partially empty conduits beneath the ground.
Lava tubes are very common formations at volcanoes.

Examples of Lava Tubes
Thurston (Nahuku) lava tube near summit caldera of Kilauea Volcano in Hawai`i Volcanoes National Park
Undara Lava Tubes, Queensland, Australia. These are the largest in the world.

Lava tube
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Copyright John Seach