SIMON FRASER / SCIENCE PHOTO LIBRARY SIMON FRASER / SCIENCE PHOTO LIBRARY
Pahoehoe lava. Cooled pahoehoe lava from a Hawaiian volcano. Pahoehoe lava may harden in smooth sheets or, as here, may ooze out and solidify into rope-like formations. This type of lava can flow at 35 miles per hour down a steep slope, while the other common form, known as a'a in Hawaiian, is rough and clinker-like and cannot move more than 30 metres in an hour. Both kinds of lava have the same chemistry, their low silica content making them viscous at temperatures above 1200 degrees celsius. This allows gases to escape easily, limiting the explosiveness of the eruption. Photographed in the Ka'u Desert, Hawaii, USA.
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