Crop circles in Finney County, Kansas, USA, 24 June 2001.
© National Aeronautics & Space Administration / Science & Society
Resembling a work of modern art, variegated green crop circles cover what was once shortgrass prairie. The most common crops in this region are corn, wheat, and sorghum. Each was at a different point of development when the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) captured this image, accounting for the varying shades of green and yellow. Healthy, growing crops are green. The crops are partly fed by water from the Ogallala Aquifer, a giant layer of underground water. The rivers and streams that fed the aquifer have long since disappeared in the geologic development of the West after the last ice age. Water now takes a long time to trickle down through the soil to recharge the aquifer, and it could run dry. For this reason, efforts are being made to conserve the water of the Ogallala Aquifer.