Next time you're flying over Moab, Utah -- OK, maybe the next time you're checking out Google Maps -- look over to see this lake of unnatural shape and colour. You can't miss it; it's the electric blue smudge in an ocean of brown rock.
These are a series of evaporation ponds for potash, or salts that contain potassium used for fertiliser. But potash is actually found deep under the surface -- where ancient lakes or inland seas have dried up -- and these evaporations ponds are only the most visible tip of a long, elaborate mining operation.
The actual potash mine is the small smudge of white at the top center of the top photo. Here, a briny solution of salt and water is pumped into deep injection wells. Brine is used instead of water to preferentially dissolve the potash, leaving other minerals in the rock 730m to 1200m underground undisturbed. Then the brine, now heavy with dissolved potash, is pumped back up into the evaporation pools.
The pools themselves are dyed dark blue to absorb and retain heat from the sun. In the hot, dry desert climate, it takes about 300 days for the brine to dry into salt and potash crystals. Machines scrape up these crystals from the bottom of these rubber-lined ponds, and they're sent off for processing. In other photos, you can see the ponds in varying shades of colour as water evaporates.
The potash mine here next to Moab, Utah, was actually built by the Texas Sulphur Company in 1963. At the time, it was a conventional mine, where workers and machines dug underground. But the same year it opened, a horrific gas explosion trapped 25 men underground, killing 18 of them. A few years later, it was converted to the solution mining system still in use today, where humans no longer have to go underground for potash. [Intrepid Potash, NASA Earth Observatory]