Micro Geomorphic Analysis of the Kofu Basin Alluvial Fans, Central Japan
Micro Geomorphic Analysis of the Kofu Basin Alluvial Fans, Central Japan
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日本中部甲府盆地冲积扇的微地貌分析
DOI：
10.5190/tga1948.39.98
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发表时间：
1987
期刊：
影响因子：
--
通讯作者：
Isao Takagi
中科院分区：
文献类型：
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作者：
Masatami Nakayama;Isao Takagi
甲府盆地的许多冲积扇按其所处的位置可分为两种类型：山麓型冲积扇和底板型冲积扇。通过对山前扇微地貌的分析，明确了山前扇的形成过程和时代，得出以下结论：1）山前扇主要是由泥石流或泥流堆积而成。该类型扇表现为大量搬运形成的碎屑流瓣或泥石流堤等微地貌; 2）以水流作用为主的底扇，微地貌表现为河道砂坝、天然堤、决口喷射等微地貌; 3）山麓型扇的粒度和微地貌受源区地质条件影响显著。该类型扇体主要由漂石和卵石组成，形成“海参型”泥石流瓣。另一方面，“岸型”泥石流堤发育在由卵石、细粒、砂和粉砂组成的山麓型扇体上。前者是紊流洪水，后者是漫滩洪水或峡谷壅水形成的。两个地区的微地貌分布格局和形态不同。
A lot of alluvial fans in the Kofu Basin can be devided into the following two types by their location; the piedmont-type fans and the floor-type fans. This study aims to make clear the processes and ages of their formation through the analysis of micro-landforms.The conclusions are as follows:1) A piedmont-type fan is mainly built up by debris flows or mud flows. This type fan displays the micro-landforms such as debris-flow lobes or mud flow levees which are formed by massive transportation.2) A floor-type fan is mainly formed by water flows and has slightly elevated microforms as channel bars, natural levees, and crevasses sprays.3) The particle sizes and micro-landforms of piedmont-type fan are significantly affected by the geological condition of its source area. This type fan constituting mainly of boulders and cobbles forms debris-flow lobes of “the trepang type”. On the other hand, the mud-flow levees of “the bank type” are developed on a piedmont-type fan composed of pebble, granule, sand and silt.4) A floor type fan is divided into the upper part and lower part. The former is formed by flood of turbulent flow and the latter by over-bank flood or back-water dammed up at gorges. Different distribution patterns and shapes of micro-landforms are observed in the two parts.