The Physics Of Moving Ski Moguls

As an avid skier I have always considered moguls to be large, immovable, obstacles. Solid piles of difficulty that haphazardly push my skis around with no regard for my intentions.

Three researchers in Colorado, David B. Bahr, W. Tad Pfeffer, and Raymond C. Browning, have discovered that moguls actually move! And not only that – they move up hill!

The math goes something like this:

A specific representation for the erosion–deposition wave W at position x created by a skier n may be given by the sinusoidal form Wn(x) = a sin(2πx/2rn + ϕn), with positive W corresponding to deposition.

The layman explanation goes something like this: as a skier turns on a mogul, snow is scraped from the bottom of one mogul to the top of the next one, having the overall effect of “moving” the moguls. And, although skiers invariably push snow down the mountain, the ski moguls move uphill.

Mogul Diagram

Below is a time-lapse photo of video showing the uphill migration of ski moguls on the Riflesight Notch ski run at Winter Park Ski Resort. The movie spans five months, starting in early December and ending in late April of the 2006/2007 ski season. Each frame of the movie represents one day.

One thought to “The Physics Of Moving Ski Moguls”

  1. Very interesting. I think this beats the old tourist fable of putting the mogels in storage for the winter. Now we can just say they crawl up the mountain!

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