GEOMORPHOLOGICAL FEATURES OF VALLEYS “DISSECTING” THE DILUVIAL UPLANDS OF SAGAMINO AND MUSASHINO, KANTO PLAIN

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  • 相模野台地・武蔵野台地を刻む谷の地形
  • 相模野台地・武蔵野台地を刻む谷の地形--風成テフラを供給された名残川の谷地形
  • サガミノダイチ ムサシノ ダイチ オ キザム タニ ノ チケイ フウセイテフラ オ キョウキュウ サレタ ナゴリガワ ノ ヤチケイ
  • GEOMORPHOLOGICAL FEATURES OF VALLEYS “DISSECTING” THE DILUVIAL UPLANDS OF SAGAMINO AND MUSASHINO, KANTO PLAIN
  • 風成テフラを供給された名残川の谷地形
  • A STUDY OF VALLEYS FORMED BY REMNANT STREAMS AND AIR-LAID TEPHRA

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In this study, geomorphological and geological features of valleys which dissect the diluvial uplands of Sagamino and Musashino, unto Plain, are investigated and a model of their evolution is also shown.<br> Diluvial uplands of the Kanto Plain such as Sagamino and Musashino have thick air-laid tephra layers on their surfaces. These tephras were supplied from westward volcanoes such as Haone and Fuji, and are estimated to have been supplied constantly by many intermittent eruptions father than by a few eruptions in short duration.<br> There must have been two processes on the upland surfaces following the formation of the uplands: stream erosion and tephra deposition for which the evolution of these valleys can be understood as a result of these reciprocal processes.<br> The purpose of this study is to clarify the evolution of these valleys under the conditions mentioned above. Geornorphological features are investigated in their planforms, longitudinal profiles and cross section forms of valleys. Geological stratigraphy along the valleys is analysed from boring data and observations of outcrops in the investigated areas.<br> Valleys investigated are those of Sakai River, Hikiji River and Hato River in Saamino and Kanda R., Shakujii R., Sen R., No R., urome R. and Toshitorazu R. in Musashlno (Fig. 1).<br> The Saamino Upland consists of some terraces groups: Zama Hills (lama stage), Koza Hills (Simosueyoshi stage), Sagamihara Surface (usasino stage), Tanahara Surface and Minahara Surface (both Tacikawa stage). The surfaces from Sagamihara Surface on are dissected fan terraces, and are covered with thick tephra layers: 17-20m on Sagamihara Surface, 6-7m on Tanahara. Surface and 2-4m on Minahara Surface. Thickness varies depending on their forming age (Figs. 2 and 3). formed by the removal of tephras along the former river courses. The model (Fig. 17) shows the evolutional history of these valleys: 1) A former river course remains on a terrace surface; 2) Remnantstreams flows away falling tephras along the former river course; 3) Tephras accumulated on both side of the stream form a “valley” and 4) A water spring may create another valley.<br> When additional “fossil channels” on diluvial uplands are discovered, they will offer further data for reconstructing river hydrology or palaeoenvironmental studies.

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