Tephrostratigraphy and Pollen Analysis of Ohnuma-aisawa Lake Deposits, Eastern Foot of Fuji Volcano, Central Japan

Tephrostratigraphical and palynological studies have been done for the Ohnuma-aisawa lake deposits, distributed at the eastern foot of Fuji Volcano. The Ohnuma-aisawa lake deposits lie over the Gotemba mud flow deposits, filling in their hollow places, and consist mainly of a lower half of sand and gravel beds and an upper half of silt and peat beds. Nearly twenty tephra beds, dating after about 2200y.B.P, were found in the upper half. The stratigraphy and characteristics of the tephra are described. The condition of the ground in the area of Ohnuma-aisawa Lake became worse after the fallout of Yu-2 tephra about 2200y.B.P. The Cryptomeria forests were dominant until the 9th century in this area. However, the destruction of the forests by human activities began with the increase of Pinus after that time.