Tale of Two Lakes : Big Pics
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Among the world's strangest lakes are those of the Ounianga Basin in northeastern Chad, deep in the Sahara Desert. These were all part of one big lake once, more than 5,500 years ago. Since then things have gotten a lot drier and sand dunes have migrated across the lake, cutting it into a series of sliver lakes.
Even more interesting: The lakes are almost all fresh water. This is because the lakes are fed by an aquifer that surfaces in this area. So even with the terrific evaporation rate of the Sahara, the water gets freshened and replenished from below.
Millennia ago Ounianga Lake was the heart of a lush landscape of wooded grasslands, according to pollen buried in ancient lake sediments. Behold the power of desertification!
Image credit: NASA (Astronaut photo ISS021-E-26475, acquired Nov. 14, 2009)
The beautiful Lake Atitlán in Guatemala is in trouble. Agricultural run-off, sewage and run-off from deforestation has enriched the lake waters with nutrients and triggered blooms of toxic cyanobacteria. The noxious bloom, as well as the towns and deforestation (grey and lighter green, respectively) are pretty easy to detect in this Nov. 22, 2009 image taken by an instrument on NASA's Terra satellite.
The Guatemala Times reports that correcting the problem with water treatment plants and other measures would cost at least $32 million.
Image credit: NASA
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