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.
Tsugaru-Juniko Lakes consist of the well-known Lake Ao-ike and other 32 lakes in Aomori Prefecture's Tsugaru Quasi-National Park, in the westernmost part of the Shirakami Mountains which has been registered as a World Natural Heritage Site. Tsugaru-Juniko Lakes is considered to have been formed by a landslide triggered by an earthquake that occurred about 300 years ago. An identification of the subsurface structure of the landslide is particularly important for an understanding of the origin of lakes ; however, such data is limited. This study investigated the subsurface structure of the landslide near the Ao-ike by using 2D high-resolution electrical resistivity providing the evidence of the formation of landslide-dammed lakes and new information of the geological data. Besides, historical documents were used to investigate the formation age of the lakes.