THE GEOMORPHIC DEVELOPMENT OF THE MIDDLE COURSE OF THE AGANO RIVER
THE GEOMORPHIC DEVELOPMENT OF THE MIDDLE COURSE OF THE AGANO RIVER
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阿贺野川中游地貌发育
DOI：
10.4157/grj.52.689
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发表时间：
1979
期刊：
影响因子：
--
通讯作者：
M. Yanagida
中科院分区：
文献类型：
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作者：
M. Yanagida
发源于日本东北部的骨干山脉，阿贺野川的中段由东向西流，在新泻市附近注入日本海。研究区以N_？？_ S向构造，并被巨厚的新生代沉积物覆盖。该地区在地貌上分为两个区域;一个是河流切割出深谷或峡谷的区域，河流阶地沿河道沿着发育良好，另一个是洪水平原发育良好的会津盆地（图1）。河流阶地沿河道中段分为沿着八级。它们分别被命名为西平阶地、柴崎阶地、德泽阶地、野泽阶地、沼泽阶地、三合阶地、大和阶地I和大和阶地II。会津盆地西部的洪泛平原分为6个等级，并与野泽阶地、板下阶地、沼泽阶地、三合阶地、大和阶地和现在的洪泛平原进行了对比（图2）。在中更新世时期，当古会津盆地延伸到现在将会津盆地与忠见河谷分开的山丘之外时，忠见川直接流入会津盆地（图8-A）。中更新世以后，会津盆地西缘活动线理的中部形成。沿着沿着这种活动线理的隆起构造了位于现在的多见河谷和会津盆地之间的边缘丘陵。当西平阶地形成时，边缘的丘陵最终与古会津盆地分离。因此，现在的阿加诺河的前身河道也开始作为一条盘曲河道穿过周边的丘陵（图8-B）。在野泽的形成过程中，这两个地区的加积条件得到了确认。阶地（图8-C）。在峡谷地区，河水的底部加深了10.20米。在会津盆地从野泽阶地形成期间（约200米），21000_？？_两万两千B。P.）沼泽浮石流沉积物的向下流动（图8-D）。大约5000年前，沼泽火山产生的厚层浮石流沉积物掩埋了忠见川流域，并散布在会津盆地的西南部。因此，大部分的德泽、野泽和板下阶地完全被掩埋在浮石流沉积物之下（图8-E）。由于浮岩流沉积物被迅速切割，根据当地的地形形成了大和阶地群。侵蚀的基本水平。150年的沉积物会津盆地中部早-中更新世户寺组沉积后，厚达200米。另一边。另一方面，阿加诺河的中游已经减少了大约。100 - 140米，在同一时期，形成8级河流阶地的斜坡上的河谷。这种差异的原因可能是会津盆地西缘活动线理划分的两个区域的地壳运动所致。
Originating from the backbone range of Northeast Japan, the middle course of the Agano River flows east to west and pours into the Sea of Japan near Niigata City. The studied area is characterized by N_??_S trending tectonic structures and covered with thick tCenozonic sediments. The area is geomorphologically divided into two regions; one is the region where the river cuts a deep valley or gorge and fluvial terraces are well developed along the course of the river, and the other is the Aizu Basin occupied with well developed floodplains (Fig. 1). The river terraces are classified into eight levels along the middle course of the river. They are named as the Nishidaira, Shibasaki, Tokusawa, Nozawa, Numazawa, Mitsuai, and Yamato I and II terraces respectively. The floodplains in the western part of the Aizu Basin are classified into six levels and correlated with the Nozawa, Bange, Numa2awa, Mitsuai, Yamato terraces, and present floodplain (Fig. 2). The Tadami River had directly flowed into the Aizu Basin during the middle Pleistocene time when the Palaeo-Aizu Basin had extended beyond the hills now separating the Aizu Basin from the Tadami River valley (Fig. 8-A). After the middle Pleistocene, central part of the active lineation in the western margin of the Aizu Basin have been formed. Uplifts along this active lineation have constructed the bordering hills locating between the present Tadami River valley and the Aizu Basin. The bordering hills were finally separated from the Paleo-Aizu Basin at the time when Nishidaira terrace was formed. Therefore, the present antecedent course of the Agano River also began to cut across the bordering hills as an entrenched meandering course (Fig. 8-B). The aggradational condition was recognized in the two regions during the formation of Nozawa. terrace (Fig. 8-C). The river deepened its floor by 10.20 meters in the gorge region, and. a few meters in the Aizu Basin during the period from the formation of Nozawa terrace (ca. 21, 000_??_22, 000 y. B. P.) to the flowing down of the Numazawa pumice flow deposits (Fig. 8-D). Thick pumice flow deposits originating from Numazawa Volcano buriedd the Tadami River valley and scattered at the southwestern part of the Aizu Basin about 5, 000 years ago. Therefore, a large propotion of Tokusawa, Nozawa, and Bange terraces were completely buried under the pumice flow deposits (Fig. 8-E). As the pumice flow deposits were rapidly cut down, Yamato terrace group was formed according to local. base levels of erosion. The sediments of 150_??_200 meters in thickness have been accumlated in the central part: of the Aizu Basin after the deposition of Todera formation of early-middle Pleistcene inn age. On the other. hand, the middle course of the Agano River has cut down about. 100 140 meters during the same period, forming eight levels of fluvial terraces on the slopes of the river valley. The difference of these process is considered to be caused by crustal movements in both regions which have been divided by the active lineation in the western margin of the Aizu Basin.