This is a fairly common question from intermediate to advanced skiers who have graduated on to skiing steeper, icier slopes at higher speeds.

The physical cause is too much pressure on a ski which is moving sideways, making it alternately grip then release in an oscillatory fashion, especially towards the end of the turn, when the pressure increases due to combined centrifugal force and gravity. The effect depends on the ski’s stiffness and damping, but it can be quite spectacular!

From a technique point of view the problem is caused by over-rotation resulting in the ski moving sideways, plus too high an edge angle for the applied pressure. The solution is to make rounder turns, especially in the all-important control phase (initiation through to fall line), so that the ski is moving forward rather than sideways, and to use the turn shape, rather than skidding, to control speed. It also helps to flex and relax the legs towards the end of the turn to absorb some of the pressure. If you need to skid the turn a bit more, try less edge angle so that the ski doesn’t try to grip as aggressively.