| 概要 |
In summer of 1980, a wide area of North Kyushu had an unusual heavy rainfall several times, resulting in that various geological hazards such as flood, river-bank bursting, landslide, rockfall, railwa...y paralyses etc., hit many places. Especially landslide and related hazards broke the main roads in the Noko Island (Noko-no-shima), Fukuoka City, and hindered daily livings of people for a long time. All the geological hazards of Noko Island in this time are related to the Kitazaki Granodiorite in origin, and are fallen into paralyses of roads and erosion of escarpments. The roads were cracked, many of which are lunar cracks, and were collapsed in places. These hazards are probably caused by the creeping down of loosed soil and/or well-weathered zone of granodiorite or by the influences of landslide occurred under the road level with a few occasion of the present artificial activities such as engineering works of road or farm. The erosion of escarpments is apparently divided into three types, landslide with slump, superficial debris-sliding and earth-fall. It seems that these landslide types are differentiated by a combination of the depth of weathered zone of the granodiorite with the inclination of escarpment and the vegetation in places. All the hazards in this time were caused by a deeply weathered granodiorite, which is loose and has a large permeability for water, except for those resulted from the load of half-weathered plateau basalt. It is supposed that the Noko Island is continuously threatened by sliding of escarpments because the geological and topographical conditions have been beyond a chance of reformation for the future.続きを見る
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