PATCHWORK ponds catch the eye in this image of the Utah desert taken by an astronaut from the International Space Station. The brilliant blues will eventually produce landscapes of vivid green. When the pond water evaporates, it will leave potassium salt, a vital fertiliser.
The 23 coloured ponds cover 160 hectares, and play a key part in the mining of potassium chloride from ore buried underground. The compound, otherwise known as muriate of potash, accounts for 95 per cent of all potash fertilisers used worldwide.
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Each pond is full of potash brine, and the colour reflects its state of evaporation. The darkest blue indicates deeper water, but it鈥檚 also this shade for another reason: the rich blue hue comes from dye added to speed up the rate at which the water absorbs sunlight and warmth, aiding evaporation. Lighter blues and sea-foam greens indicate ponds with shallower water and less dye. The tan ponds are dry, with just a layer of potassium salt crystals left.
The ponds contrast with the high desert of the Colorado plateau, which sits 1600 metres above sea level. The darker green areas along the river are the only lush vegetation in the picture.
This article appeared in print under the headline 鈥淭rue blue鈥�
