Utah stains

An astronaut on the International Space Station took this photograph of solar evaporation ponds outside the city of Moab, Utah, close to the Colorado River. The 23 colourful ponds spread across 162 hectares, are part of a large potassium chloride mine. The colour of each pond indicates a different state of evaporation. The deep royal blue is caused by dye added to full ponds of potash brine and water, in order to increase the rate of heat absorption. Sea-foam greens indicate shallower waters that are well into the evaporation process. Tan ponds are nearly dry, and white zones comprise the end product – crystals – awaiting harvest.