土地改変と土壌 (大規模土地改変と第4紀研究<シンポジウム>)

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Land transformation on hilly land usually aims at grading steeper slopes and creating gentle or nearly flat land surfaces. The process contains cutting the soil mantle at a higher portion, transporting it and filling a lower portion with it.A large-scale land transformation could mean that a large part of the original soil loses its exposure on the new surface by burial or removal. The criterion for it may be the exposure width (along the slope direction) of the soil being less than half of the total width of the new surface which is composed of filled material in the lower part and exposed material beneath the soil in the upper part, leaving the original soil between the both. Geometry tells us that the thinner the soil and the steeper the slope, the more the said criterion is satisfied.One should limit the soil, as pedology does, to the one having A and B horizons or A horizon when B horizon is lacking. Thickness of soil thus defined is usually no more than 1-2 meters on slope, hence satisfying the criterion in most cases. C horizon and even unconsolidated or semiconsolidated geological bed may often get utilized as new soil material.New soils can be treated as a man-made immature type because in fill zone, on the one hand, the original soil profile is hidden deep beneath the disturbed or mixed fill material either of the original soil itself or of non-soil material and in cut zone, on the other hand, C or D horizon of the original profile is brought to the surface.It is worth notice that a large-scale land transformation changes a complicated land form into a simpler one but makes the distribution of the soil materials more complicated. Before the transformation the soil is located parallel to the land surface, but after that the new surface is divided into three different zones: fill, original soil, and cut. The horizontal distribution pattern of the zones is variable and irregular depending on the initial land form and the mode of transformation. A tendency of regularity, however, is found as follows: in the original soil and the cut zones the soil horizons appear reversely to those in the normal profile, the upper the horizon the lower the position of the appearance, while in the fill zone the upper part of the original soil profile comes first nearer to the bottom.
日本第四紀学会の論文

土地改変と土壌 (大規模土地改変と第4紀研究<シンポジウム>)

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