Pop the top off a can of mixed nuts and, chances are, Brazil nuts will be at the top. This phenomenon, of large particles tending to rise to the top of mixtures while small particles tend to sink down, is popularly known as the “Brazil nut effect” and more technically as granular segregation.
Pop the top off a can of mixed nuts and, chances are, Brazil nuts will be at the top. This phenomenon, of large particles tending to rise to the top of mixtures while small particles tend to sink down, is popularly known as the “Brazil nut effect” and more technically as granular segregation.
Look down at the top of a riverbed and it’s easy to draw a parallel: the top of a riverbed is typically lined with larger cobbles, while finer sand and small gravel particles make up the deeper layers.
Physicists concerned with particle movement have given a lot of thought to the mechanics by which particles sort in these types of scenarios, but that research has not been translated to earth science until now. In a new study, geophysicists from the University of Pennsylvania found that granular segregation helps explain the tendency of riverbeds to be lined by, or “armored” with, a layer of relatively larger particles.
Published in the journal Nature Communications, the findings enhance understanding of how riverbeds form, with implications for how rivers may also erode. But the research also makes new insights into the fundamental physics of particle segregation, which apply to all sorts of granular materials, from riverbeds and soils to industrial and pharmaceutical substances.
Read more at University of Pennsylvania
Image: An experimental 'stream' -- a circular channel with varying sizes of particles and fluid embedded with fluorescent dye -- enabled the Penn team to examine the forces influencing the sorting of rocks in a riverbed. (Credit: University of Pennsylvania)
