地形特性による巨大扇状地と沖積扇状地の比較
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概要
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Megafans have been discussed whether they are alluvial fans or not. Alluvial fan areas and slopes are controlled mainly by drainage basin areas and relief ratios. Hence, the Kosi megafan, Okavango fan, and five megafans in the Gran Chco to the east of the Andes are examined, on the basis of relationships among four geomorphic features, that is drainage basin areas, relief ratios, fan areas and fan slopes. Alluvial fans are chosen in west circum-Pacific mobile belt, that is Japan, Taiwan, the Philipines and New Zealand.The points of seven megafans are around regression lines between fan areas and fan slopes of alluvial fans, and are beyond regression lines between drainage basin areas and fan areas of alluvial fans. The points of six megafans except the Okavango fan are under regression lines between relief ratios and fan slopes of alluvial fans, and are around regression lines between drainage-basin areas and relief ratios.Drainage basin features of six megafans except the Okavango fan are similar to those of alluvial fans, because of relationships between drainage basin areas and relief ratios. As the relief ratio of the drainage basin of the Okavango fan is extremely small, the process of the Okavango fan formation seems to be different from those of alluvial fans in west circum-Pacific mobile belt. Furthermore, formation processes of six megafans are considered to be different from those of alluvial fans, because six megafans except the Okavango fan are large and gentle not only absolutely but also comparatively. The megafan features which are comparatively large and gentle seem to bring similar features of alluvial fans.Alluvial fans in the tropical humid General Valley in Costa Rica, the semi-arid San Joaquin Valley, and arid Death Valley in the United States are comparatively large than those in west circum-Pacific mobile belt. Hence, the comparison between these alluvial fans and megafans will be required in future.
- 埼玉大学教育学部地理学研究室の論文
埼玉大学教育学部地理学研究室 | 論文
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