大山火山東麓天神川流域における地形面の分布について
スポンサーリンク
概要
- 論文の詳細を見る
The purpose of the present study is to make clear the geomorphological characteristices of the gentle slopes at the foot of Daisen Volcano. The Tenjin River drainage basin is the greatest in the middle part of Tottori Prefecture. The Takeda River, the main stream of the upper part of the Tenjin River, runs through the region of granitic rock. The Ogamo River, one of the main tributaries of the Tenjin River, streams in a dissected valley of Daisen Volcano. Based upon the observation on the distribution and topographical characteristices of the geomorphic surfaces, the facies of the deposits and the volcanic ash beds, It is concluded that the higher river terrace, the middle river terrace and the second-lower terrace in the volcanic region can be corresponded to those three surfaces in the non volcanic region. From the facts that the longitudinal profiles of the depositional surfaces and the facies of the deposits of the river terraces are similar to those of river bed, It is considered that those river terraces were formed by the relative changes of the base level of erosion. On the other hand, The older volcanic foot fan and the first-lower river terrace cannot be recognized in the non volcanic region, and are the peculiar geomorphic surfaces to the volcanic region. In the upper stream of the oldre volcanic foot fan and the first-lower river terrace, there are the depositional surfaces formed by the pyroclastic flows. The longitudinal profiles of these deposisional surfaces are straight, and the inclinations of the depositional surfaces are steeper than the old volcanic foot fan, the river terraces and the river bed. The deposits of the pyroclastic flows consist of poorly sorted and non welded materials of andesites. The fragments of andesites are some what vesiculated, and the dry density of the fragment is the smollest of the other volcanic rocks in this area. The proportion of the fine particles contained in the pyroclastic flow deposits is larger than that of the other deposits. From the above-mentioned topographical characteristices of the depositional surfaces and the facies of the pyroclastic flow deposits, It is assumed that at the time when the pyroclastic flow materials are deposited in the upper part of the river, the river loses the balance of the erosion, transportation and deposition. After that, the river can keep another new equilibrium. The river bed under another new equilibrium of the dissected valley are the older volcanic foot fan and first-lower river terrace surfaces.
- 湘南工科大学の論文
- 1975-03-31