Abstract
Pit excavation survey for marsh deposits burying landslide depression was carried out to clarify formative age of the Nakanosawa landslide located in Mts. Shirakami, Northeastern Japan, from a view point of evolution of mountain slopes since Late Pleistocene. The deposits of two metres in thickness consisiting of peat, fallen timbers and volcanic ashes were excavated. They overlaydebris deposited by a landslide at the bottom. Wooden fragments collected from just above the landslide deposits are date back to 7.6ka to 8.1ka by radiocarbon method. Presumed formative age of Nakanosawa landslide is early Holocene as late as 8ka, because soil layer covering the debris deposits has not developed.
