English: Archway cave, Undara National Park, Queensland Australia. The area is situated within the McBride volcanic province and contains 164 volcanoes, vents and cones. The lava tubes are regarded amongst the largest and longest on the planet. A lava tube is a type of lava cave formed when a low-viscosity lava flow develops a continuous and hard crust, which thickens and forms a roof above the still-flowing lava stream. The tubes at Undara are thought to have followed water courses and other natural depressions. The word Undara is aboriginal in origin and means a long way.
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