DIRK WIERSMA / SCIENCE PHOTO LIBRARY DIRK WIERSMA / SCIENCE PHOTO LIBRARY
Columnar basalt rock in a hanging formation on a cliff at the edge of a waterfall (not seen). Pentagonal or hexagonal columns of basalt are formed during the cooling of extrusive, igneous rock. This is rock that has formed from lava that has risen to the Earth's surface due to volcanic activity. More than 90 percent of volcanic rocks are basaltic. Photographed at Svartifoss in Skaftafell National Park, Iceland.
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