片状岩のクリープ性大規模崩壊  [in Japanese] Creep-type Large-scale Landslides of Well-cleaved Argillaceous Rocks  [in Japanese]

Large-scale landslides due to rock-creeping occur frequently in the tectonite zone of orogenic belts where well-cleaved argillaceous rocks such as slate, chert-laminite and slump breccia are widely distributed. These landslides are well observed in the Kyushu mountains. They can be detected by careful photo-interpretation because they have similar topographic features as follows. Double ridges (Doppelgraten), step eliffs and extension gashes are well developed in the top of the slide area. Creeping of well-cleaved argillites results in bulging or swelling topography in the base of the area where small-scale collapses are frequently observed. Chert-laminite has higher ductility contrast than other eleaved argillites because chert is more competent than sandstone or mudstone. Therefore, large-scale landslides are habitually occurred in the area underlain by chert-laminite or slump breceia with chert-laminite matrix.