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 The wave-detection system of "A lineatus" and other surface feeding fish is tuned to match the waves that signal prey in their environment. "A lineatus" feeds on aquatic, semi-aquatic and terrestrial insects, often insects that have just touched the surface of the water or have fallen in and are struggling at the surface. Abiotic sources give off capillary waves of frequency 8–14 Hz, while biotic sources give off much higher frequencies, anywhere from 12–45 Hz and above. This correlates well with "A lineatus’" peak sensitivity at higher frequencies. Wave stimuli are classified into two types: the first is click stimuli