Skylight in lava tube from Puu Oo Eruption of Kilauea Volcano in Hawaii. The color of the lava is an indication of its temperature -- bright red about 1100 degrees C; dull red about 1000 degrees C. The surface of the lava cools rapidly by radiation heat loss while the lava just below the surface is still much hotter. Brightness of the red color is thus an indicator of how fast the lava is stirring and overturning. The shining gray pahoehoe at the edges of the skylight is older lava that has cooled to nearly atmospheric temperature.                  U.S. Geological Survey photo by Jim Kauahikaua.

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