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The colors of Sunset

Sunset Crater view Sunset Crater Volcano was originally named Sunset Mountain by that intrepid explorer of the Colorado River, John Wesley Powell, for the bright sunset reds and yellows of its summit. Of all the cinder cones of the San Francisco volcanic field, Sunset Crater Volcano is one of the most colorful and pristine.
Black basalt cinders Most of the rock you see at Sunset Crater Volcano National Monument is dark gray to black basalt. Basalt is rich in iron and magnesium-bearing minerals, which give it its dark color. While the base of Sunset Crater Volcano is mantled with dark gray cinders, the summit of the cinder cone is a striking rusty red. Although you might speculate that the rocks at the top are of a different type, they are not! What makes these basalt cinders red?
Red basalt cinders produced by oxidation or rusting of iron rich minerals Searing basalt lava was not the only material to erupt from Sunset Crater Volcano! The cinder cone also belched forth hot gasses. The cinders on the rim of the cinder cone were bathed in these vapors and chemically reacted with them to form iron oxide (rust), sulfur compounds, and gypsum. The resulting red, yellow, purple, and green-colored basalt cinders decorate Sunset Crater Volcano’s summit.
Many visitors to the National Monument notice splotches of greens and yellows on the basalt surface. These splotches are actually lichen. Continue on to the next stop to learn about these early colonizers of lava flows.

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This page was last updated on 6/24/99

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