August 27, 2008
A salt devil is a dust devil on a salt flat or saline playa, where salt is lofted into the air in a narrow, rotating column. Dust devils are formed by Rayleigh-Taylor instability, a fluid-dynamic phenomenon. Sunlight heats the air near the ground and it becomes convectively unstable, so it rises. Surface dust is drawn into the air, rushing radially inward along the ground and into the spinning updraft. Dust devils range from half a yard wide and a few yards tall to over 30 feet wide and over 3,000 feet high. They can rotate either clockwise or counterclockwise. Their spin direction is not controlled by the Coriolis force as some people have suggested.
Here we see a salt devil in the Saline Valley, a remote, arid region of Death Valley National Park, in eastern California. For about four hours the heated dry lake spawned salt devils that were blown around the lake by local winds. Most lasted less than a minute while others swept around the lake for over three minutes. The “salt” consisted of powdery, water-soluble compounds such as NaCl (sodium chloride, the primary ingredient in table salt), KCl (potassium chloride, used chiefly as a fertilizer), NaHCO3 (Sodium bicarbonate), Na2CO3 (Sodium carbonate, also known as washing soda), Na2SO4 (sodium sulfate, used in detergents), and similar minerals, all of which are white. Photo taken on March 2, 2008.