G. BRAD LEWIS / SCIENCE PHOTO LIBRARY G. BRAD LEWIS / SCIENCE PHOTO LIBRARY
Lava tube in Kilauea volcano, in the Hawaii Volcanoes National Park, Hawaii, USA. Lava tubes form when the surface of a lava flow cools and solidifies, while the interior remains molten. The molten lava then flows through a hollow passage of cooled rock. Here, part of the roof of the tube has collapsed, allowing a view into the tube.
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