DIRK WIERSMA / SCIENCE PHOTO LIBRARY DIRK WIERSMA / SCIENCE PHOTO LIBRARY
Solidified pahoehoe lava. Lava is molten rock that is expelled when a volcano erupts. Pahoehoe is basaltic lava that has a very smooth surface. Although it is viscous, pahoehoe has a low melting point, which means that it can travel great distances before solidifying. If it solidifies as it is flowing, it can form billowed, folded shapes, as here. This sample measures 190 millimetres across.
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