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Title: Mount St. Helens, 18 May 1980

Description: Here is a good example of a very high Reynolds number turbulent jet. The photo and the following text was taken from an article by Peter Bradshaw, entitled "Turbulence," in Sci. Prog. Oxf. (1981), vol. 67, pp. 185-204. " Over a few hours in the initial stages of the eruption the energy released was the equivalent of about 10-50 megatons of high explosive. A rather small fraction of this energy went into the turbulence -- unsteady, billowing, eddying motion -- in the plume shown in the photograph. The shape of the plume represents some sort of complicated time integral of the velocity fluctuation field, and its fantastic sculpture -- the larger protrusions are several hundred metres across -- seems to portray the unusual violence of the phenomenon within. In fact, plumes whose boundaries are almost as convoluted can be produced quite easily in the kitchen sink. .....Fill a sink, bucket, or best of all a glass-walled tank with water, and allow to settle for half an hour so that the turbulence generated by the filling process has more or less subsided. Make up a solution of cellulose wood-filler powder or similar material, thin enough so that it still pours easily. Hold a teaspoon of the solution just above the water surface and pour it in quickly. The solution, being heavier than water, will fall toward the bottom of the vessel entraining, and being diluted by, clear water as it goes. Just before the first of the solution reaches the bottom of the vessel, the plume will look rather like that in (the photo)."



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