Changes of the Water-level of Lake Suwa During Alluvial Epoch

Abstract

Lake Suwa occupies the northwestern part of Suwa Basin which is the highest among fault basins in the Fossa Magna zone of Central Japan. Its area is 14.3 km2 and the waterlevel is 757 m above the sea.It has been generally believed that the water-level of this lake went down gradually by the deepening of outlet's gorge and its area reduced with the growth of alluvial lowlands. However, my full investigation with respect to locations of many archaeological sites and remains in this basin, has made clear that five stages of low water-level and four stages of high water-level existed from non-ceramic age to present alternately. These facts are summarized as follows : First stage of low water-level Later period of nonceramic ageBeginning of earlier Jomon ageFirst stage of high water-level Earlier Jomon ageMiddle period of early Jomon ageSecond stage of low water-level Middle period of early Jomon ageLater period of early Jomon ageSecond stage of high water-level Later period of early Jomon ageBeginning of middle Jomon ageThird stage of low water-level Beginning of middle Jomon ageLater period of middle Jomon ageThird stage of high water-level Later period of middle Jomon ageBeginning of late Jomon ageFourth stage of low water-level Middle period of late Jomon ageMiddle Yayoi ageFourth stage of high water-level Middle Yayoi ageLate Yaoyi ageFifth stage of low water-level Late Yayoi agepresent