Saturday, September 29, 2012

Posturing On The Alluvial Fan

  An alluvial fan by definition is formed by the action of water. But in adopting an Earth-based or restricted point of view we can introduce a perceptual illusion like that of a mirage when we see water when it is not actually present. One finds geological features on Earth which are similar in appearance to the alluvial fan such as debris flows and other forms of mass wasting. An interesting case is that of the talus cones seen found in Svalbard.
src: Wikipedia
  Note in the image above that for each talus there is a funneling cone at the top, a channel and a debris field below. One can identify similar features at Gale Crater on Mars. Mountains to the north of the crater rim can act as a funneling cone. There is also a channel through the crater wall and a debris field but the slopes differ. The structure is somewhat like that of the Galton board which was introduced to illustrate the normal distribution. It too has a funnel, a channel and a cascade through which objects fall. The fan and the talus cone are flow fields for the material that is deposited below the channel. In the case of the alluvial fan one could generalize and to include some other flow field besides that of water to move material about. Mt Sharp appears to be more consolidated than the material around it since it appears to have withstood erosion better but we will have to wait and see what the actual data turns up before we can speak with any authority. Referring to an alluvial fan is just a first impression.

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