This image displays several nice examples (see the subimage) of classical "alcove-channel-apron" gullies in a 10 kilometer (about 6 miles) diameter crater located in Mars' northern mid-latitudes.
The alcove is the cupped area near the crater rim where rock has eroded and been transported through the gully. The channel is the narrow route through which all of the alcove material is transported. That material is then deposited into the fan-shaped apron near the crater floor.
In 2006 the Mars Orbiter Camera (MOC) found evidence of new changes to the deposits in some Martian gullies. The formation mechanism for gullies on Mars is therefore an important topic of current debate: while gullies can form in the presence of water, there are also dry formation mechanisms that can produce very similar features. Scientists study gullies in part to try to help clarify the question of the history of water on Mars.
Photo credit: NASA/JPL/University of Arizona
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