Contaminants can move UP a flowing stream of water

An interesting observation has been posted in MIT's Technology Review - that contaminants in water (or other liquids) can move against the dominant flow by using countercurrents, and can even traverse small waterfalls.  The discovery came through classic serendipity:

While pouring the hot water onto the [herb] leaves, Ernesto Althsuler and buddies at the University of Havana in Cuba, noticed a puzzling phenomenon. They found that, sometimes, the leaves would somehow travel upstream and end up contaminating the upstream container of pure water.

Being diligent physicists, they decided to investigate. They found that the leaves (and also chalk powder) were able to navigate upstream if the waterfall was less than about a centimetre in height. "For distances of the order of 1 cm or less, some of the floating particles eventually start to "climb up the stream"," they say.

Details at the link.  It has potential implications for "chemical, medical, pharmaceutical and industrial processes."

Via Swans on Tea.