Country: United States
Date: May 2007
What is the white foam around rocks in fast moving rivers?
Foam forms when gases are trapped in water as bubbles and these bubbles
are stabilized (do not readily burst). Many substances can cause the
stabilization of air bubbles in water. Naturally occurring organic
compounds, wastes dumped into rivers, detritus from river organisms -
all of these can cause the bubbles to stabilize and not burst readily.
It is not so much that organic compounds are present only in fast moving
rivers. Rather, since bubbles form more readily in roiling water (where air
and water are mixed because of the turbulence of the water) we get more bubbles
formed in turbulent rivers and these bubbles are then stabilized by the presence
of organic compounds.
Greg (Roberto Gregorius)
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Update: June 2012