琴引浜における鳴砂の発音特性の変動とその要因

摘要

琴引浜における鳴砂の発音特性の低下原因を解明するために，5調査地点で6年間，鳴砂の発音特性の変動とその要巨引こついて調査した。その結果，発音特性に著しく影響を及ぼす水以外にもシルト及び粘土あるいは海水からの析出塩類が砂粒子表面に付着することにより，発音特性を低下させていることが分かった。このシルト及び粘土は，鳴砂と同じ石英，長石が含まれ，しかも，長石成分は鳴砂と比較すると多く含まれている。また，これらの粒径は約10μm以下に風化あるいは摩砕されている。なお，このシルト及び粘土の砂層への混入は主に人為的なものと考えられることから，その防除対策を立てる必要がある。%The change in the sound-producing property of singing sand and its controlling factors were investigated at five investigation spots at Kotohikihama-beach over 6 years in order to clarify the factors in the deterioration of the sound-producing property of singing sand. As a result, it was proven that the sound-producing property deteriorated with the adherence of precipitated salts from seawater or silts and clays to the sand particle surface, which, except for moisture, markedly affects the sound-producing property. Such silts and clays had compositions the same as singing sand, and it was found that the feldspar component was more abundant than that in singing sand. Their particle size was about 10 μm or less caused by weathering or abrasion. Still, it is necessary to take removal countermeasure for these silts and clays, because the contamination of these materials in the sand layer seems to be mainly artificial. Surfactants and tobacco ashes that affect the sound-producing property were also investigated. However, these effects in the field could not be observed. The effect on singing sand by the NAKHODKA heavy oil spill incident, which occurred in 1997 during the investigation period, was also investigated. The pollution effect on singing sand by heavy oil was observed. However, it was found that the sound-producing property did not deteriorate ever in the presence of the oil.