Journal of Geography (Chigaku Zasshi)
Online ISSN : 1884-0884
Print ISSN : 0022-135X
ISSN-L : 0022-135X
Volume 118, Issue 4
Displaying 1-12 of 12 articles from this issue
Original Articles
  • A Comparative Study of Naka and Kinu-Kokai River Basins
    2009 Volume 118 Issue 4 Pages 611-630
    Published: August 25, 2009
    Released on J-STAGE: March 26, 2010
     The purpose of this study is to propose a method for analyzing regional factors to understand the quantitative characteristics of water supply-demand system on watershed scale. The Naka River basin and the Kinu-Kokai River basin are the study areas selected for a comparative discussion. In particular, urban residential water supply systems of Mito and Mitsukaido cities, which are located in far downstream areas of the Naka and Kinu-Kokai River basins, respectively, are surveyed. In this study, three regional factors are examined— landform, land use, and water rights. Concretely, basin form ratio and basin relief ratio by main tributary basin are calculated first. Then, land use combination types by tributary basin are clarified using modified Weaver's method. Finally, the spatial and quantitative characteristics of water demand in the Naka and Kinu-Kokai River basins are analyzed with data on water rights. As a result of the case study, the analytical indicators and methodological approach this study proposes demonstrate their utility in a discussion of problems associated with urban water resources on watershed scale.
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  • Towhida RASHID, Md. Hossain MONSUR, Shigeyuki SUZUKI, Nobuo OOI
    2009 Volume 118 Issue 4 Pages 631-645
    Published: August 25, 2009
    Released on J-STAGE: March 26, 2010
     This paper provides a detailed description of sedimentary facies including pollen and diatom analyses, and 14C ages obtained from a hand-excavated outcrop in the central part of the Bengal Lowland. Based on this examination, seven sedimentary facies were recognized in relation to relative sea-level (RSL) changes since the mid Holocene. With the help of a standard reference datum, the required Mean Sea Level (MSL) has been calculated at the surface of the outcrop. The top of the outcrop was about 1.9 m above MSL and the base is 4.1 m below the MSL. The lowermost bioturbated sand flat facies, 3.75 m below the present MSL, contains mangrove pollen and represents an intertidal coastal-plain and estuarine-channel deposits that were dominated by tidal current. A 14C age of 7570-7430 cal BP was obtained for this unit. The evidence supports a transgressive mode in the Bay of Bengal during the middle-Holocene epoch. A subsequent regression interval was found in a salt marsh facies before 6670-6410 cal BP. The salt marsh facies has a sharp contact with an underlying (lower) mud flat facies, shaped by downcutting of the upper bed, indicating a regression. In response to this regression, the environment changed gradually from a mud flat to a salt marsh. The salt-marsh deposits contain abundant mangrove pollens and marine- and brackish-water diatoms, providing support for inflow of shallow-marine water into a supratidal, brackish-water mangal environment. The bioturbated mud flat facies indicates that the succession was dominated by tidal current, and the relative sea-level started to rise again after a small rebound. Hence, the transgressive conditions prevailed during the deposition of this mud flat facies in an intertidal coastal-plain environment. The underlying bluish-black medium-bedded peat layer contains grass pollen. This indicates that after the mid-Holocene the environment around the site changed gradually from mangrove to fresh-water swamp vegetation, in response to regression of the bay between 4080-4030 cal BP.
     The above evidence suggests that the central part of the Bengal Lowland represented as an intertidal to supratidal coastal-plain estuarine environment that experienced with mid-Holocene relative sea-level changes between 7570-7430 and 4080-4030 cal BP.
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  • Analysis of Kyomachiya (Traditional Wooden Townhouse) Demolitions
    Kazumasa HANAOKA
    2009 Volume 118 Issue 4 Pages 646-664
    Published: August 25, 2009
    Released on J-STAGE: March 26, 2010
     The purpose of this article is to evaluate a social simulation using a dynamic spatial microsimulation model for predicting demolitions of Kyomachiya, which are traditional wooden townhouses and core elements of the historical landscape of Kyoto City, Japan. This model is also applied to estimate the number of Kyomachiya surviving when preservation policies are introduced. The results are summarized as follows:
     (a) Spatially disaggregated synthetic microdata of Kyomachiya residents were constructed by combining multiple existing datasets in a manner whereby the sums of synthetic microdata agree with those of census datasets. Using synthetic microdata allows us to analyze detailed household demographics and the process of Kyomachiya demolitions at small area and individual levels.
     (b) Decision-making units such as individuals, households, and Kyomachiya can be modeled in the same way that they exist, behave, and interact with each other in the real world using object-oriented modeling. Another merit is that re-using and extending classes are possible due to object-oriented architecture.
     (c) The results of simulations show that, during the next 15 years, only 67.3% of Kyomachiya will be preserved and the proportion of the population aged 60 and over will increase from 43.9% to 51.6%. On the other hand, when a comprehensive preservation policy is implemented, those numbers are reduced to 82.5% and 49.2%, respectively. In this manner, a dynamic spatial microsimulation model is useful for understanding the process and cause-and-effect of Kyomachiya demolitions under the status quo. Furthermore, what-if simulations on the basis of Kyomachiya preservation policies help to evaluate which policy is most effective for reducing the number of demolitions.
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  • Takashi OGAMI, Toshihiko SUGAI, Osamu FUJIWARA, Masaaki YAMAGUCHI, Eij ...
    2009 Volume 118 Issue 4 Pages 665-685
    Published: August 25, 2009
    Released on J-STAGE: March 26, 2010
     The depositional process of the Latest Pleistocene to Holocene shallow-marine and fluvial successions is investigated using five 14C-dated borehole cores from the Kiso River delta, central Japan. The delta succession provides high-quality records of the transgression and regression of an enclosed delta system and reveals the development of fluvial-dominated coastal lowlands.
     Based on a facies analysis, the cored sediments are classified into five sedimentary units: A) basal gravel, B) fluvial and intertidal sand and silt, C) transgressive lag deposit, prodelta mud, and sandy silt, D) delta-front-slope sandy silt and sand, and delta-front-platform sand, and, E) delta-plain and fluvial sand and silt. Detailed age-depth curves of these cores are reconstructed based on 108 AMS 14C ages including 83 new 14C ages. These curves show patterns similar to those of temporal variations in accumulation rates, and are divided into four sections (I to IV) from the base to the top: I mainly consists of unit B with rapid accumulation (7.3-21.4mm/yr); II mainly consists of unit C with moderate accumulation (2.4-2.8mm/yr); III mainly consists of unit D with rapid accumulation (6.7-17.8mm/yr); and, IV consists of unit D and E with moderate accumulation (1.3-3.9mm/yr).
     The section boundaries of I/II and II/III, which coincide with the unit boundaries of B/C and C/D, reflect the inundation of a flood plain by seawater, developing a bay environment, and the subsequent progradation of the delta–front slope, respectively. The ages of these boundaries constrain the estimation of the expanding rate of the bay and progradation rates of the delta. The expanding rate of the bay is estimated at 10m/yr during the period 10200-7900 cal yrs BP, and the progradation rates of the delta are 3-4m/yr (6500-4100 cal yrs BP), 5m/yr (4100-1300 cal yrs BP), and 10m/yr (1300 cal yrs BP to the present). These age data indicate that the transition from transgression to regression occurred between 7800 and 7300 cal yrs BP.
     The geological cross-section along the Kiso River along with the isochrones constructed by over a hundred 14C dates indicates the following depositional history of the Kiso River delta: (1) from 10000 to 7280 cal yrs BP (K-Ah horizon) —During the expansion of the bay, onlap of unit C on unit B is visible, and unit C overlapped all the core sites just before the K-Ah fall, and (2) from 7280 cal yrs BP to present—Isochrones younger than 6500 cal yrs BP are similar to each other and cross the unit boundaries of C/D and D/E. This demonstrates that units C–E are contemporaneous heterotopic facies formed in response to delta progradation after the K-Ah fall.
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  • Martin RADVANEC
    2009 Volume 118 Issue 4 Pages 686-699
    Published: August 25, 2009
    Released on J-STAGE: March 26, 2010
     The extreme effect of the heat rays of the A-bomb explosion on August 6, 1945 at 8:15 a.m. in Hiroshima was studied on two tile fragments that had been excavated during the period from 1977 to 1982 from the west bank of Motoyasu River, about 100 m down the river from the Motoyasu bridge. A number of very hot and melted fragments, which the shock wave brought from buildings that were smashed at the hypocenter 1.318 s after the explosion, were deposited on the west bank of the river. The pieces of tile possibly came from the destroyed stone wall of the Sei Hospital, the Saikoji Temple, and/or the Sairenji Temple, and were quickly cooled by the river water.
     The tile fragments were composed of andesitic pyroclastic rock and their surfaces were melted to a depth of 3.18 mm. The glass crust had a variable andesite and basalt-andesite composition, which are the melt products of cristobalite and/or tridymite, pigeonite (XFe = Fe/(Fe + Mg) = 0.37-0.44), hornblende (XFe = 0.33-0.42), labradorite (Ab48.2-40.6An51.8-55.5Or0-3.9), and K-feldspar (Ab8.2Or91.8). The temperature of 6287°C was calculated on the surface of an object at the hypocenter after the explosion, according to the depth of 3.18 mm of the melt and different depths and melting points of above mentioned minerals. This surface temperature was deduced by the extrapolating of the depth-temperature relationship obtained by the mineral-relicts between 2.68 and 3.18 mm of depth. According to the regression line T = -1715.1d + 6287 (d is the depth) with R2 = 0.989, the temperature gradient in the andesite tile was 1715°C/mm, reaching a depth from 2.86 to 3.18 mm, where the volume of glass and volume of primary minerals (rock) are equal. For a depth of more than 3.64 mm, the structure and mineral assemblage of pyroclastic andesite rock has an initial composition.
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  • Teruki IWATSUKI, Eiichi ISHII, Tadafumi NIIZATO
    2009 Volume 118 Issue 4 Pages 700-716
    Published: August 25, 2009
    Released on J-STAGE: March 26, 2010
     A methodology to estimate long-term hydrochemical evolution of deep underground is indispensable for the safe geological isolation of high-level radioactive waste (HLW). This study demonstrates the methodology by illustrating scenarios of past geological events, processes, and their interrelationships with present-day hydrochemical conditions. Besides, we infer long-term variations of groundwater chemistry at Horonobe, Hokkaido, Japan.
     The region is underlain mainly by Neogene to Quaternary marine sedimentary rocks, (the Wakkanai Formation (Fm) and the overlying Koetoi Fm: siliceous and diatomaceous mudstones). During various events in the geological past, such as deposition, compaction, uplift, and denudation, and the more recent Neotectonic activities in this area, highly permeable hydrogeological structures formed at depths not over than 400m below ground level in the Wakkanai Fm. The hydrogeological system can be subdivided into three hydrogeological sub-systems: (1) overlying, relatively low permeability Koetoi Fm., (2) highly permeable, upper Wakkanai Fm at depths less than 400m and (3) relatively low permeability Wakkanai Fm, at depths greater than 400m. The present-day hydrochemical conditions in each sub-system have been influenced by hydrogeological properties and hydraulic conditions over a long period. In subsystems 1 and 2, recharging with meteoric water flushed connate seawater during uplifting and denudation during the last 1Ma. In contrast, fossil seawater with one-third to one-half the salinity of present-day seawater has been preserved in subsystem 3.
     The relatively low permeability sequence in sub-system 3 was formed by the compaction of diatomaceous mudstone during subsidence prior to 1.0Ma. After that, changes of climatic conditions and geographical features would not have influenced groundwater flow. The groundwater chemistry evolved from seawater during long-term geochemical diagenesis in a relatively closed system. The long-term variations of salinity probably range from that of seawater to that of present-day groundwater. The occurrence of secondary minerals shows that the buffer reactions of carbonate and sulphide minerals have preserved the near neutral pH and reducing condition since initial diagenesis immediately after deposition of the rock formation.
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Short Article
Report on the 12th Geological Field Trip of the Tokyo Geographical Society
Book Reviews