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 for the first, a loudspeaker is set up facing the water surface, while a plastic disc covers the front of the speaker cone with a small hole in the center, allowing air to be pushed through the hole to stimulate the water surface in a pattern controlled by a square-wave generator. Alternatively, a small rod a few millimeters in diameter is dipped briefly a few centimeters into the water. Either setup can be moved around the tank to deliver stimuli at various locations. The loudspeaker setup offers the advantage that stimuli can be precisely controlled to mimic natural stimuli or