芦田川水系の河川争奪と天然記念物「久井・矢野の岩海」の形成

広島大学総合博物館研究報告 Issue 14 Page 33-44 published_at 2022-12-25
アクセス数 : 480
ダウンロード数 : 138

今月のアクセス数 : 11
今月のダウンロード数 : 2
File
BullHiroshimaUnivMuseum_14_33.pdf 22.7 MB 種類 : fulltext
Title ( jpn )
芦田川水系の河川争奪と天然記念物「久井・矢野の岩海」の形成
Title ( eng )
Piracy of the Ashidagawa River System and Formation Mechanism of the Kui and Yano Boulder Fields
Creator
MORI Wataru
YAMANAKA Tomoru
Source Title
広島大学総合博物館研究報告
Bulletin of the Hiroshima University Museum
Issue 14
Start Page 33
End Page 44
Number of Pages 12
Journal Identifire
[PISSN] 1884-4243
[EISSN] 1884-3999
[NCID] AA12459864
Abstract
国の天然記念物である「久井・矢野の岩海」は巨礫が谷底に集積した特殊な地形である。花崗岩の風化とともに,細粒物質のみが侵食,除去されることにより,コアストーンが残留した「疑似岩塊流」とされる。コアストーンは花崗岩域で普遍的に生成されるが,岩海は約14km 離れた指定地付近に限られる。一方で,いずれの地点も争奪河川の分水界近くに位置する。本研究では,芦田川の河川争奪地形および久井の岩海の地形を記載し,それらの発達について考察した。その結果,いずれの岩海の指定地も,争奪河川の最上流に位置するものの,河川争奪が生じても数十m程度のわずかに下刻が生じるような絶妙な地形環境であったと考えられた。
The boulder fields in Kui and Yano of Hiroshima prefecture, which are national natural treasures of Japan, have unique topographies where large granite boulders accumulate along valley bottoms. The Cretaceous granite had weathered since the Sera upland low-relief mountain surface was developed in the middle of the Miocene epoch. The fine-grained weathering material had been washed away from the valley, and only the core stones remained in the designated sites. These are known as “pseudo block streams” based on the process and cause of the topography. Core stones are universally generated by granite weathering. However, the boulder fields are distributed only in two designated areas, 14 km away from each other. Both sites are located near the watersheds of the Ashidagawa and Gonokawa river systems. In this study, we described the piracy topography of the Ashidagawa River and the Kui boulder field topography and examined these developments. The Ashidagawa River, downflowing to the Seto Inland Sea, captured the upper stream of the Gonokawa River system, probably due to the subsidence of the Seto Inland Sea. The designated sites are located within the rare topographical environment in the uppermost reaches of the piracy rivers, where slight erosion with a depth of several tens of meters has occurred.
Keywords
河川争奪
コアストーン
岩海
岩塊流
piracy
core stone
boulder field
block stream
Language
jpn
Resource Type departmental bulletin paper
Publisher
広島大学総合博物館
Hiroshima University Museum
Date of Issued 2022-12-25
Rights
Copyright (c) 2022 広島大学総合博物館 Hiroshima University Museum
Publish Type Version of Record
Access Rights open access