Agriculture on the outer part of an alluvial fan
A reader from Germany alerted me to a cool image from the Terra satellite. This is from southern Iran and shows how they are dealing with the lack of fertile ground and water in this desert region.
The greenish colors in the image below highlight the distribution of agricultural land on the depositional landforms in the valley (clicking on the image will take you to a much larger [3 MB] version of the image directly from the NASA Terra site).
The image below zooms in to the beautiful alluvial fan. Note how the agricultural land is out on the outer part of the fan. In most alluvial fans there typically an overall decrease in grain size in a downfan direction — that is, coarser-grained material in the updip (proximal) areas of the fan and finer-grained material in the outer (distal) fan. What the exact grain size distribution is for this fan depends a lot on the rock types in the mountainous area being eroded but the trend from proximal to distal is common.
In this case, my educated guess is that the farmers are taking advantage of the finer-grained deposits out on the outer part of the fan. It would be fun to get on the ground and test that idea. I also wonder how they deal with water. The gray bifurcating threads in the upper-left part of the fan are the currently-active channels — perhaps they capture water during active periods and then distribute to other regions?
Perhaps some of you know of other examples of alluvial fan agriculture?