Umi is located along the Kamimura River within the Kamiyahagi area of southeastern Ena City, Gifu Prefecture. The name 'Umi' means sea or large lake; however, there are no lakes in the mountainous Kamiyahagi area. The Tokai Gou (torrential rain) flood of September 11-12, 2000 destroyed embankments along the river, and exposed sedimentary layers that are typical of a lacustrine depositional setting. This confirms the existence of a paleo-lake from which the name Umi originated. The ^<14>C ages, ranging from 280±37 to 345±25 BP, appear to be contemporaneous with Tensho Earthquake that occurred in central Japan on January 18, 1586.