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.
"Techniques using these isotopes have become increasingly popular," says Cutler, "as ways of finding out the sources and ages of sediments and other rock deposits."
Bierman says that "there has been little testing of a fundamental aspect of the method, however--the similarity of isotope abundance over time. In Namibia we now have huge run-off and a chance to test this assumption of consistency."
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.
Namibia's rains stopped months ago, but the groundwater table is so high that there is still flow in some streams and rivers.
Almost every river crossing shows the effects--logs, mud and bridges torn asunder. In some streams, the scientists saw minnows and frogs stranded in pools. "They must have been delivered during the flood," says Bierman.
In a few places, water, road damage and stream beds laden with sediment kept the researchers from collecting samples from the exact same places as in previous years.
"The riverbed four-by-four truck tracks we needed to get to sample sites were sometimes gone," says Bierma
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| Contact: Cheryl Dybas cdybas@nsf.gov 703-292-7734 National Science Foundation Source:Eurekalert |
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