著者

石井 武政 磯部 一洋 相原 輝雄

出版者

Japan Association for Quaternary Research

雑誌

第四紀研究 (ISSN:04182642)

巻号頁・発行日

vol.26, no.1, pp.85-92, 1987-05-31 (Released:2009-08-21)

参考文献数

18

被引用文献数

1 1

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Gentle slopes are distributed between uplands and lowlands in the Tsukuba Upland area, Ibaraki Prefecture, Japan. These slopes are dominant on the left bank side of streams flowing to the west and on the right bank side of streams flowing to the southeast. Opposite side slopes, in contrast, are generally steep. In other words, topography along the streams in upland areas shows an asymmetrical valley pattern.Drilling samples show that the upland is occupied, from top to baseward, by the Younger Loam (equivalent to the Tachikawa and Musashino Loams) and the Joso and Narita Formations of Quaternary age. The gentle slopes are underlain by slope deposits of poorly sorted silty sands and gravels 1-3 meters thick. The deposits consist of particles essentially derived from the Joso Formation.The slope deposits lie unconformably on the Joso and Narita Formations and are overlain by the upper Younger Loam which has AT (Aira-Tn Volcanic Ash) dated at 21, 000-22, 000y. B. P. in its basal part.This stratigraphic evidence indicates that the slope deposits were formed during the last glacial age. It is assumed, from the relation between the slope direction and the frequency of slope cryoturbation in the winter season, that the slope deposits were accumulated by refrigeration in the cold climates of the late Pleistocene.

著者

安原 正也 丸井 敦尚 布施谷 正人 石井 武政

出版者

公益社団法人 日本地理学会

雑誌

地理学評論 Ser. A

巻号頁・発行日

vol.64, no.10, pp.719-727, 1991

被引用文献数

6

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The Tsukuba Upland, about 390 km² in area, is one of the diluvial uplands commonly found in the Kanto Plain (Fig. 1). The upland is composed of the Younger Kanto Loam (about 3m thick at most), the Joso Formation, and the Kioroshi Formation in descending order. In the upper part of the Joso Formation is a less-permeable clay/silt layer called the Joso Clay (Fig. 2). The present study aims at clarifying the physical properties of the Joso Clay, which are important from the hydrological point of view.<br> The Joso Clay was sampled at 19 points on the Tsukuba Upland for determination of its physical properties (_??_ in Fig. 1). The Younger Kanto Loam and the sands, situated above and below the Joso Clay, respectively, were also sampled for a comparison of physical properties. In addition, some data on physical properties of the Joso Clay were obtained from the literature (0 in Fig. 1).<br> Saturated hydraulic conductivities of the Joso Clay proved to be extremely low, ranging from 8.29&times;10^-6 to 5.30&times;10^-9cm/sec with an average value of 1.39&times;10^-6cm/sec (Table 1). The Joso Clay presented a remarkable contrast in saturated hydraulic conductivity to both the overlying Younger Kanto Loam and the underlying sands, showing differences of two to three and three to five orders of magnitude, respectively (Fig. 3).<br> The porosity of the Joso Clay was between 54% and 77%. The Joso Clay showed a high degree of variability in thickness, from 15 to 400cm (Fig. 4). No macropores or non-capillary pores with the pore diameters larger than 3.8&times;10^-2mm were found in the Joso Clay (Fig. 5), indicating that almost all the water in the Joso Clay moves very sluggishly.<br> Based on the results of this study, vertical subsurface water movement in surface parts of the Tsukuba Upland is assumed to be substantially restricted due to the presence of the Joso Clay.

著者

菅野 敏夫 石井 武政 黒田 和男

出版者

公益社団法人 日本地下水学会

雑誌

日本地下水学会会誌 (ISSN:00290602)

巻号頁・発行日

vol.28, no.1, pp.25-32, 1986 (Released:2012-12-11)

参考文献数

11

被引用文献数

1 3

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Water level of Lake Kawaguchi in Yamanashi Prefecture had risen more than 3 m above the standard level after the heavy rainfalls in summer of 1983. On that opportunity the authors started to study the hydrogeological conditions around the lake with the use of long-term observation data of the lake water level, groundwater level, precipitation and others (Figs.4 and 5).The area is composed mainly of the Tertiary Misaka Group and the Quaternary volcanic rocks extruded from Fuji Volcano (Fig.1). The Misaka Group and the Kofuji Mud-flow Deposits, one of the effusive rocks of the volcano, constitute the hydrogeological impermeable bed rocks.Although Lake Kawaguchi has no natural mouth for surface discharge, the water is drained off through the man-made tunnels. On the other hand, it is likely that the water permeates through the volcanic rocks into the underground valley about 5 km south of the lake, judging from the contour line of the groundwater level (Fig.2). Figures 2 and 3 indicate that the hydrogeological watershed of the lake occupies only the northern part of the topographic watershed which extends southwards to the top of Mt. Fuji.The lake water is recharged from the surrounding mountains of the Misaka Group. The lake water remarkably rises after the 3 days rainfall reaches more than 200 mm (Figs.6 and 7). When the 3 days rainfall is less than 100 mm, it is invisible. Fluctuations of the lake water coincide with the rainfall pattern (Fig.4). The graph of the accumulation value of the rainfall variation is similar to the fluctuation of the lake water level.