横浜港周辺における海食崖と砂嘴の発達に関する一考察

概要

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Formation of the barrier where the central part of Yokohama City is located was investigated by the comparison of old maps and geological surveys. This barrier was formed as the sand spit extending northwestward from the end of Ishikawa Upland. Behind this barrier, lowland mainly composed of alluvial cohesive soil extends. In this area, jet of sand and subsidence of structural foundation were observed during the Kanto Great Earthquake. Thus, the understanding of the formation of this barrier and lowland is important to consider potential vulnerability of this area. Comparison of profiles along several sections crossing Ishikawa Upland showed that sand was supplied from this upland while forming sea cliff. Supplied sand was carried by longshore sand transport caused by wind waves in Tokyo Bay. In this area predominant wind directions are N and NE. Waves from these directions make large incident angle greater than 45 degrees reference to the shoreline direction, and this large wave incidence accelerates the formation of sand spit by the mechanism given by Ashuton et al. (2001).
2003-04-25