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 sensitive range of 75–100 Hz. Fish are also sensitive to waves generated within 7–30 cm of the fish’s location, though they can occur at any point within that radius. Because the water surface acts as a low pass filter, this radius is different for different wave frequencies: 70 Hz waves with 100μm peak-to-peak distance are subthreshold at 37 cm, and 140 Hz waves are subthreshold at 19 cm. Fish are able to tell apart concurrent waves of different frequencies when the frequencies are different by at least 15%, though at certain frequencies this difference can be as low as 8%.