ISS060-E-77289
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Spacecraft nadir point: 17.8° N, 15.2° E

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Spacecraft Altitude: 222 nautical miles (411km)
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Image Caption: Desert Contrasts in Chad

An astronaut aboard the International Space Station (ISS) shot this photograph of stark desert contrasts in northwestern Chad. The geologically young, dark lava flows of the Tousside volcano stand out from the older, lighter rocks of the Tibesti Mountains and the sands of the central Sahara Desert.

A large portion of the Tibesti Mountains is volcanic in origin. Successive effusive eruptions have formed extensive plateaus that cover older sedimentary rocks. Looking north of Tousside (left in this image), erosion has helped carve the expansive network of canyons. Eolian activity has also played a role: that is, winds have brought lightly colored sands from the north into low-lying areas between the mountainous ridges.

The contrast of color created by flows from Tousside and other volcanoes in northern Africa has captured astronaut's attention for decades. The terrain of the Tibesti mountains is difficult to access, but remote sensing provides a useful means to perform geologic investigations here.