2021 Volume 58 Issue 3 Pages 95-108
Regarding landslide topography in western Aomori Prefecture, classified as Neogene accounts for 82.7％ of the whole. Particularly, 33.4％ are sedimentary rocks between the Neogene middle period Miocene and Pliocene. Mineralogical analysis of boring core of the “Nuruyu area” (pumice tuff) composed mainly of these sedimentary rocks and the Iwasaki landslide area (black mudstone) was performed for each depth. The “Hydrothermal alteration zone” for each depth is distinguished based on past studies, with discussion of the relation with the slip surface.
A landslide body including the slip surface was found at the hydrothermal alteration zone (I zone : cristobalite-smectite band) defined by smectite, cristobalite, and halloysite, including copious amounts of smectite. Therefore, it may be possible to judge the slip surface from the combination of minerals. In addition, a large amount of smectite due to low-temperature hydrothermal alteration is considered to be a predisposing factor for landslides. In addition, Neogene landslides in this area are thought to have been widely affected by low-temperature hydrothermal alteration due to green-tuff movement. This is why landslides occur so often in the area.
