Sunday, December 7, 2008

A beautiful alluvial fan from space.

I subscribe to Nasa's Earth Observatory "Image of the Day," something I highly recommend. Last week their set included this satellite photo of an alluvial fan in the Zagros Mountains of southern Iraq.

The story it tells is mysterious, rich, and beautiful.

Clearly there are discrete zones where agriculture is possible, and imposed on that are radiating agricultural property lines (the long, thin rectangles) reminiscent of 18th century French survey lines you still see in around St. Louis today.

I really can't figure out the topography. Clearly there's a strong break at the base of the fan, but even upstream of that the channel is braided, indicating a low slope.

Nasa's description tells some of the story - the area is very arid, so a braided channel might be found on a steep slope that has infrequent floods.

Surely that strong NW-SE line at the base of the fan has some recent tectonic origin, or perhaps the valley, like California's Owen's valley, is formed in a graben.

I don't know, does anybody? (Looks like I'm right about the tectonics, I may yet learn some geology.)

I see this excellent blog beat me to this image.

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