Mars: Gullies of Gorgonus Chaos PIA03826
This fractured surface belongs to a portion of a region called Gorgonum Chaos located in the southern hemisphere of Mars. Upon closer examination one finds that these gullies and alluvial deposits, initially discovered by Mars Global Surveyor, are visible on the trough walls (best seen near the bottom of the image). These gullies appear to emanate from a specific layer in the walls. The gullies have been proposed to have formed by the subsurface release of water.
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Image Credit: NASA/JPL/Arizona State University  

This fractured surface belongs to a portion of a region called Gorgonum Chaos located in the southern hemisphere of Mars. Upon closer examination one finds that these gullies and alluvial deposits, initially discovered by Mars Global Surveyor, are visible on the trough walls. These gullies appear to emanate from a specific layer in the walls. The gullies have been proposed to have formed by the subsurface release of water. Gullies are trenches cut into the land as accelerated streams of water (or another liquid) erode the surface. To see these focus on the trenches at the bottom of the image. Running down the walls of the trough are the thin, dark lines of the gullies. Beneath the grooved, gully channels are faint, softer-looking fans of material. These are called alluvial deposits. Alluvial simply means all of the sand, gravel, and dirt that is carried and deposited by a liquid. On Earth, that liquid is typically water. As the liquid carves the gully, the eroded material from the channels get carried along and deposited below in fan-like shapes.  
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