粘土鉱物からみた八甲田山周辺に分布する火山灰土壌の母材の起源

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In this paper, we discuss the origin of parent material of "volcanic ash soil" in Hakkoda mountains, Northeast Japan. In the Hakkoda mountains, we observe two distinct tephra layers named To-a (Towada-a ash fall deposit: c.a. 1,000yr. B.P.) and Cu (Chuseri pumice fall deposit: c.a. 5,000yr. B.P.) in the volcanic ash soil. Humic layers as defined as A-horizon above To-a and buried A-horizons above Cu are developed, respectively. For identifying the origin of parent material, we analyze the mineral in the volcanic ash soil by X-ray diffract method. The dominant clay minerals in the A-horizon are smectite, 14-10A mixed layer minerals and quartz. And the buried A-horizons have clay fraction dominated by Al-vermicurite and quartz. In silt fraction of these horizons, quartz, feldspar and amorphous minerals are dominant. On the contrary, crystalline clay minerals and quartz are very scarce in both silt and clay fractions of To-a and Cu. As quartz are scarcely contained in primary deposits of the tephra and its weathering products, quartz in the volcanic ash soil would be transported from other areas. Therefore, the material of fine fraction would mainly be derived from non-volcanic material supposed to be eolian deposits. On the other hand, reworked material of coarse fraction in A horizon and buried A horizons would be from tephra. From the result mentioned above, we conclude that the parent material of the volcanic ash soil in the Hakkoda Mountains has been derived from the coarse reworked material originated from tephra with little contamination of non-volcanic eolian fine material.
日本ペドロジー学会の論文
1988-06-30

粘土鉱物からみた八甲田山周辺に分布する火山灰土壌の母材の起源

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