Sastrugi Sastrugi Sastrugi, or zastrugi, are sharp irregular grooves or ridges formed on a snow surface by wind erosion, saltation of snow particles, and deposition, and found in polar and open sites such as frozen lakes in cold temperate regions. The ridges are usually perpendicular to the prevailing winds; they are steep on the windward side and sloping to the leeward side. Smaller irregularities of this type are known as ripples (small, ~10 mm high) or wind ridges. Larger features are especially troublesome to skiers and snowboarders. Traveling on the irregular surface of sastrugi can be very tiring, and can risk
Surface states be satisfied for each formula_24 separately and for each formula_24 a single, but generally different energy level for the surface state is obtained. A surface state is described by the energy formula_26 and its wave vector formula_24 parallel to the surface, while a bulk state is characterized by both formula_28 and formula_29 wave numbers. In the two-dimensional Brillouin zone of the surface, for each value of formula_28 therefore a rod of formula_29 is extending into the three-dimensional Brillouin zone of the Bulk. Bulk energy bands that are being cut by these rods allow states that penetrate deep into the crystal.