bild

Lava tube. View of red molten lava through a hole in a lava tube. Lava tubes form when an active volcano releases a stream of lava onto the ground. The lava in contact with the air cools and solidifies into folded, convoluted rock. The lava at the centre remains molten, and flows through the new tube. Holes occur where there are weakn- esses, usually in the roof of the tube, as here. Photographed on Kilauea Volcano, Hawaii, USA. (KEYSTONE/SCIENCE PHOTO LIBRARY/BERNHARD EDMAIER)