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Whistling sand or barking sand is sand that produces sound. The sound emission may be caused by wind passing over dunes or by walking on the sand. Certain conditions have to come together to create singing sand: # The sand grains have to be round and between 0.1 and 0.5 mm in diameter. # The sand has to contain silica. # The sand needs to be at a certain humidity. The most common frequency emitted seems to be close to 450 Hz. There are various theories about the singing sand mechanism. It has been proposed that the sound frequency is controlled by the shear rate. Others have suggested that the frequency of vibration is related to the thickness of the dry surface layer of sand. The sound waves bounce back and forth between the surface of the dune and the surface of the moist layer, creating a resonance that increases the sound's volume. The noise may be generated by friction between the grains or by the compression of air between them. Other sounds that can be emitted by sand have been described as "roaring" or "booming". The particular note produced by the dune, between 60 and 105 hertz, is controlled by the rate of collision in the shear band separating the avalanche from the static part of the dune. For spontaneous avalanches, the frequency is controlled by gravity and by the size of the sand grains. The total length of the landform is about 185 kilometres. ==In dunes== Singing sand dunes, an example of the phenomenon of singing sand, produce a sound described as roaring, booming, squeaking, or the "Song of Dunes". This is a natural sound phenomenon of up to 105 decibels, lasting as long as several minutes, that occurs in about 35 desert locations around the world. The sound is similar to a loud, low-pitch, rumble, and it emanates from the crescent-shaped dunes, or barchans. The sound emission accompanies a slumping or avalanching movement of the sand, usually triggered by wind passing over the dune or by someone walking near the crest. Examples of singing sand dunes include California's Kelso Dunes and Eureka Dunes; sugar sand beaches and Warren Dunes in southwestern Michigan; Sand Mountain in Nevada; the Booming Dunes in the Namib Desert, Africa; Porth Oer (also known as Whistling Sands) near Aberdaron in Wales; Indiana Dunes in Indiana; Barking Sands in Hawaiʻi; Mingsha Shan in Dunhuang, China; Kotogahama Beach in Odashi, Japan; Singing Beach in Manchester-by-the-Sea, Massachusetts; near Mesaieed in Qatar; and Gebel Naqous, near el-Tor, South Sinai, Egypt. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「singing sand」の詳細全文を読む スポンサード リンク
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