小笠原諸島(父島・母島)の地形と土壌 : 段丘地形と土壌生成

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The results obtained were summarized as follows: (1) The coastal terraces have developed in the Bonin Islands. These terraces were divided into three terrace groups, namely, the higher (between 100 and 130 m altitude in Chichijima, between 100 and 140 m altitude in Hahajima), the middle (between 50 and 90 m altitude in both) and the lower terrace (between 20 and 30 m altitude in Chichijima, between 20 and 40 m altitude in Hahajima). (2) It was recongnized that there was a definite regularity related to the age of terrace surface in the soil distribution. The distribution of Red soil was restricted on relatively higher terrace surface. Red soil covered with Dark red soil distributed on the middle terrace surface. Slighty dark red soil distiributed on the lower terrace, while yellowish brown soil distributed on the depression and gentle slope surface. Dark soil also occurred locally at small depression adjacent to terraces as shown in Figure 2. (3) The mineral composition of Red soil was characterized by dominant magnetite. On the other hand, the mineral composition of Dark soil and Slighty dark soil were characterized by dominant weathered grain of reddish brown color as shown in Figure 3. (4) Red soils showed extremely strong acid reaction (pH 4.41-4.68). Red soils covered with Dark red soil and Dark soil showed weakly acid and slightly acid (pH 5.85-6.80), respectively. (5) The amount of dithonite-citrate-bicar bonate soluble ferric oxides (Fed) increased along with the series of Dark soils → Dark soil/Red soil → Red soils. The progress of weathering resulted in the increase of Fed. This was observed in the case of Red soil which was considered to have received maximum weathering.
1993-12-31

小笠原諸島(父島・母島)の地形と土壌 : 段丘地形と土壌生成

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