China is of course planning to employ other sources, like wind power, hydropower and nuclear, but the sooty black rock is expected to represent as much power generation as all those others combined.

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Footpaths wind gently upward to the Berber hamlet of Tamatert, wedged snugly between two stern rock faces.

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Currently, Spirit is examining a series of specimens that were perhaps formed when wind-borne volcanic ash fell to the ground, mixed with water and eventually formed into layered rock.

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At first glance, it might seem obvious that it was through the action of flowing water (fluvial), but the Curiosity team needs to rule out the possibility that these rocks were deposited by the wind (aeolian) or by some kind of surge, such as the fast-moving clouds of gas and rock that will often plummet down the sides of particular types of volcano (a pyroclastic surge).

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