| Singing sands is still a mystery of science, so it is a new approach researching singing sands employed the methods of quaternary geology and other interdisciplines. The largest area of singing sands of the world is Badain Jaran desert, and it is the ideal place for singing sands studying for their large quantity of singing dunes and dunes singing by themselves.The SE of Badain Jaran desert, 39°31′-59′N ,102°15′-35′E,about 1000km2 of sand field, was selected as study area.9 new singing duns were identified in the desert, which were scattered 3 areas: Baoritaolegai, Badain Lake and Sumijilin. Details of the singing dunes were mapped, which were combined with field investigation data.Main material features and mechanical parameters were fixed by tests of mineralogy, partical analysis and SEM of over 300 samples collected from SE Badain Jaran Desert.A dominated mineral of singing sands is quartz, over 50% of the total. Most of the sands are composed of medium and fine sand, its diameter range from 1 to 3φ, and fair well sorted, unstable skewness, narrow to fair narrow kurtosis. Singing sands are unimodal normal distribution, which are classed as 4 types. Most sand grains are oblate, mean sphericity is 0.51. Roundness is 0.41, subround.There was spatial corelation between natural singing sand and labortory singing sands by analysing the digital signals of singing sands. Foundmental acoustic features of singing sands were: loudness of the natural and laboratory singing sands are range from -30 - -20dB, and basic frequency of natural singing sands are fixed in 190Hz, of laboratory is around 1000Hz.Field investgation and simulation analysising were show that sing sands are developed on the slip face (lee face) of the revwesing barchanoid ridge and compoundd crescentic dunes with zonal distribution, whose repose are range from 27°to 32°, be close to interdune lakes.The crest of dunes is a turning point of loudness, where is the lowest loudness. Microrelief developed on the slip face and interdune lakes next to the singing dunes affected the forming of singing sands. Factors such as macroscopical or microcosmic morphometric patterns and their arrangement, mechanical characteristics, surface textures, relative humidity, the weight were contribuated to the development of the singing sands. Affects to the loundness canused by shape and roundness was so tiny that they could be neglected; however, the grainsize fraction configuration and surface terrian partly controled the singing mechanism. Thin film about 2-3μm were covered the surface of the singing sands grains, which were sediment of SiO2。Dense cracks developed on the thin film of sand grain surface were distinct features of singing sands grains surface comparied to mute sands.The correlation between loudness of singing sands and grain size parameter are limited; however the threshold of particlesize related with changes of frequency band. In fact, sand grains range from 100-300μm is the fundamental element to forming the basic frequency of the singing sands; grains less 100μm contribute to promoted the loudness of low frequency band, and grains more than 500μm are helpful to increase the loudness of high frequency band. There is also low relativity between loudness and shape, roundness of gains in experiment. Silent sands can be change to singing sands by washing with ultrasonic wave and concentrated hydrochloric acid, furthermore, surface texture such as fissuring and upturned cleavages are the key factor to singing of the sands.Singing sands was a kind of special sands, and its forming and distribuation correlated with interdune lakes , circulation of water vapor and dunes motion. Booming by dunes may be lead by the avalanches of the dune induced by vertical change of local atmospheric pressure. In the course of avalanches grains with coarse surface collide each other forming slip layers due to the rigid of the base of the dune, so collective vibration of the dune are magnified forming the booming. |
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