The Surprising Motion of Ski Moguls
Oct 9 2013
Ski moguls form on virtually all ski runs that are not mechanically flattened with grooming equipment. Those amazingly ordered structures are not planned or constructed; they organize spontaneously as a consequence of skiers turning and moving snow. Although phenomena that arise from self-organization are common, the moguls’ high visibility, ubiquity, and regularity make them a particularly surprising and impressive consequence of such seemingly random actions as ski turns. Ostensibly, skiers can turn when and where they please. Moreover, a skier’s turning radius depends on a variety of factors, including ski length and shape, snow conditions, skier ability, and the details of the skier’s knees and legs, which act as damped springs with a characteristic frequency. Nevertheless, the independent acts of many skiers form rows of moguls that not only space themselves in a regular checkerboard pattern (see panel a of the figure) but also migrate over time. And, although skiers invariably push snow down the mountain, the ski moguls move uphill.
Here is a pretty cool time lapse of mogul movement.