いわゆる火山灰土(ローム)の成因に関する一考察 : 中部-関東に分布する火山灰土の層厚分布(<特集>堆積物による火山噴火史研究)

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So-called kazanbaido which means volcanic-ash-soil in a literal translation overlies surfaces and hill slopes in most area of the Japanese island. In 1960's, the kazanbaido with massive structure and brown color was recognized as residual soil (not transported soil) which was originated from pyroclastic deposits. Recently, most studies regard the kazanbaido as soil formed through the accumulation of dispersal tephra, eolian dusts from the Asian continent and local eolian dusts. In this study, the author discusses the source of the material constructing kazanbaido on the basis of the pattern of change in its thickness (Fig. 1). The kazanbaido treated here has accumulated during the last 50,000 years in central Japan. Thickness of the kazanbaido distributed along the Japan Sea coast and in the south part of the Shizuoka Prefecture is less than 1 m. Source of the kazanbaido seems to be a lot of fine distal air-fall deposits which derived from distant volcanoes, a long-range transported eolian dust from the Asian continent, and local eolian dust from the adjacent non-vegetated area. Kazanbaido thicker than 2 m distributes in the South Kanto and North Kanto areas. Increase in the thickness of the kazanbaido in these areas is most likely caused by depositions of tephras derived from near volcanoes. Two main depositional processes of accumulation of the thick kazanbaido are as follows. One is frequent accumulation of a minor air-fall deposit associated with a small-scale eruption, which does not form stratification because of the small volume of each deposit. The other is accumulation of secondary tephras, which are derived from the slope of a volcano through wind transportation. Change in thickness in the Kanto area suggests that the former is more significant than the latter.
特定非営利活動法人日本火山学会の論文
1995-07-31

いわゆる火山灰土(ローム)の成因に関する一考察 : 中部-関東に分布する火山灰土の層厚分布(<特集>堆積物による火山噴火史研究)

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