Coastal Lowland in the Soma Area, Fukushima Prefecture

Abstract

Hilis and coastal lowlands alternate in the coastal area of Fukushima Prefecture. The coastal lowlands are uplifted drowned valleys. The author investigated Soma area in the northern part of this coastal area, and is especially concerned with the Jomon transgression, and the landforms consisting of fluival deposits and surface material. The sea seems to have reached up to the 5m contour line during early Jomon time and bays were formed. The speed of aggradation depends on the scale of rivers which flowed down the coastal lowland.There are some differences in the development of landforms and surface materials at each coastal lowland. On the coastal lowlands with small rivers, fluvial deposits are hardly found and mucky soils are widely distributed. On the other hand, on the coastal lowlands with large rivers, floodplains and natural levees develop well. But, there are some differences between Nakamura area and Haramachi area, in spite of the same scale of rivers flowing. In the Haramachi area, sandy and gravelly soil develops more than Nakamura area, and its river carries gravel to the coast. By the way, coast in the Haramachi area is rapidly retreated and it is said that since terrace building southern area of this coast is uplifted compared with the northern area. These bring the differences.In conclusion, the author considers that shoreline process, scale of river and tectonic movement are important factors for the development of coastal lowlands.