Sunday, September 18, 2011

Climate change transforms Namibian landscape

Mark Dunphy in Irish Weather Online: In stark contrasts to many other parts of the African continent the riverbeds of western Namibia, known as the land of arid deserts, are awash in water. Usually, western Namibia is a dusty place where the stream beds are sand and the “lakes” are nothing more than flats of dried mud. This year, however, rivers with names like Swakop and Omaruru and Kuiseb flowed all the way to the sea–something they don’t do often, “maybe once a decade,” says Paul Bierman of the University of Vermont in Burlington, Vt.

Along with his geoscientist colleague, Kyle Nichols of Skidmore College, Bierman has recently completed a study trip to the western mountains and coastal plain of the sparsely populated African country. The rivers didn’t just flow for a day or two, Nichols and Bierman say, they ran from the desert to the ocean for weeks on end.

“There was so much water,” says Bierman, “that people went swimming, they went tubing, and the desert turned green around rivers carrying so much sediment they were chocolate-brown.” The rains were unprecedented in both their intensity and duration. “There’s nothing like this widespread, heavy rain in the historic record,” says Nichols.

There they collected river sediment and rock at many of the sites they had sampled in 1997, 2001 and 2010. Their hope is to discover whether sediment carried by rivers in such “mega-floods” is coming from sources that are the same as those when sediment is transported by more “normal” events.

They work with collaborators at the Lawrence Livermore National Laboratory, counting rare isotopes, or sub-types, of elements formed in the mineral quartz. The results provide valuable information about the samples. “The research focuses on the use of isotopes of the chemical elements beryllium, cesium and lead to measure erosion rates and determine sediment sources,” says Paul Cutler, program director in NSF’s Division of Earth Sciences, which awarded the grant.

...It will be months before the geologists have the first results, but the effects of the torrential rains and floods in Namibia in early 2011 are clearly evident, they say. Grass covers what should be barren stony desert, and there is water in streams, something Nichols and Bierman haven’t seen before....

Dunes in Sossusvlei region, Namib-Naukluft National Park, Namib Desert, Namibia, shot by (Luca Galuzzi), Wikimedia Commons, under the Creative Commons Attribution-Share Alike 2.5 Generic license

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