Desert alluvial fan, satellite image. North is at top. Desert areas can sometimes go for years without rain, and then intense storms will cause flooding that fills old dry river beds and forms new ones. The area soon dries out again, leaving these patterns behind. The white, green and blue areas show differing levels of moisture locked into the soil. This alluvial fan is on the southern edge of the Taklamakan Desert in western China. The area shown in this image is around 60 kilometres wide. The image data includes infrared wavelengths, and was obtained on 2 May 2002, using the ASTER sensor on the Terra satellite.