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 wave detection by animals 14 cm. As the wave source gets farther from a fish, the fish’s ability to accurately determine distance decreases until it can no longer detect the waves. "A lineatus" uses the shape of the waveform to determine distance by analyzing how much the waveform has changed since it was generated; this amount of change is extremely predictable and regular. The surface waveform has high frequencies near source, and lower frequencies farther away due to the dampening effect of the water surface; the amount of decrease diminishes with distance. "A lineatus’" possible use of the wavefront’s curvature can be excluded since