Jesus Face on Peru Mountain

Stumbled across this image on google maps, which looks like a shadowy face carved into a sand dune in Peru, about 22km west of Arequipa:


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This same image appears on the aerial views at both Bing Maps and Mapquest (extreme zoom below):



After googling "Jesus Face in Peru," I managed to find two or three other references to this illusion, with no explanations for it:

http://www.geckoandfly.com/2006/10/03/strange-google-earth-objects/

http://www.gearthhacks.com/dlfile546/Optical-Illusion-(Jesus)-in-Peru.htm

http://www.sheffieldforum.co.uk/showthread.php?t=49453

http://blogs.discovermagazine.com/badastronomy/2005/07/20/more-pareidolia/

http://www.theregister.co.uk/2005/07/15/google_spots_jesus/


So. Does anyone have an explanation?