Journal of Geography (Chigaku Zasshi)
Online ISSN : 1884-0884
Print ISSN : 0022-135X
ISSN-L : 0022-135X
Current issue
Showing 1-7 articles out of 7 articles from the selected issue
  • 2020 Volume 129 Issue 3 Pages Cover03_01-Cover03_02
    Published: June 25, 2020
    Released: July 11, 2020
    JOURNALS FREE ACCESS

     Lake Khubsugul, a high-altitude (1645 m above sea-level) fresh-water lake in northern Mongolia adjacent to the Russian border, is the second largest lake in Mongolia, extending ca. 140 km N–S and ca. 35 km E–W. Its name, Khubsugul or “blue water” in the local language, derives from its maximum depth of 262 m and high water transparency. Due to its high latitude and altitude, the lake is totally frozen during winter, allowing no human activity around it in the past, with the exception of reindeer farming. In contrast, summer tourism has become extremely popular recently with winter sports now becoming trendy, either. Even in mid-August, a snow blizzard welcomed us during the morning immediately after taking this photo under a blue sky. This convinced us of a rare alleged sighting of a snow leopard in the neighboring mountains.

     Lake Baikal, which is much larger, is located ca. 200 km ENE in southern Siberia. These two lakes were formed together as N–S trending rifted basins during the late Cenozoic continental extension in central Asia. Lake Khubsugul is thought to have formed in the late Neogene to early Quaternary, but details have not yet been revealed. Mountains, at over 3000 m-high to the west, display rugged, snow-covered landscapes even in summer, and are almost identical to those of the European Alps. Precambrian to Lower Cambrian sedimentary rocks penetrated by Paleozoic granitoids in these mountains record the geotectonic history of the Central Asian orogenic belt, in which several continental blocks (Siberia, North China, Tarim, etc.) successively collided or amalgamated with each other, destroying plural oceans in between.

    (Photograph & Explanation: Yukio ISOZAKI)

    Download PDF (2529K)
Original Articles
  • Moto KAWAMATA, Yusuke SUGANUMA, Koichiro DOI, Takanobu SAWAGAKI, Akihi ...
    2020 Volume 129 Issue 3 Pages 315-336
    Published: June 25, 2020
    Released: July 11, 2020
    JOURNALS FREE ACCESS

     The purpose of geomorphological studies in East Antarctica is to understand past fluctuations of the Antarctic Ice Sheet, which is essential to constrain ice sheet models and predict future behavior of the East Antarctic Ice Sheet. Here we show a deglacial history of Skarvsnes, at the southern part of the Soya Coast, East Antarctica based on a geomorphological field survey and newly obtained surface exposure ages. Bedrock higher than ca. 250 m a.s.l. at the northwest part of Skarvsnes (Skjegget) is weathered extensively, whereas bedrock below ca. 250 m a.s.l. is relatively unweathered. The degree of weathering of bedrock above 250 m a.s.l. is similar to that at the northern part of the Soya Coast, which is thought to have been ice-free throughout the last glacial period. Therefore, a clear difference in the degree of weathering depending on altitude probably indicates the lower limit of the ice sheet elevation during the last glacial period at Skarvsnes. Judging from the multiple directions of glacial striae, the ice sheet covering the area retreated while changing flow direction under the influence of the bedrock topography after the last glacial period. Since ca. 9 ka, the ice sheet is thought to have thinned and eventually divided into two major ice streams (northward and southward) that were obstructed by a 362 m a.s.l. mountain (Shirasuso-Yama), at the southeastern part of Skarvsnes. However, the timing of the initiation of the ice sheet retreat and its duration remain unclear. Therefore, additional surface exposure ages from various areas and heights at Skarvsnes are required for a detailed reconstruction of the ice retreat history and to understand its mechanism.

    Download PDF (5089K)
  • Kohei YOSHIDA, Hideo TAKAGI
    2020 Volume 129 Issue 3 Pages 337-354
    Published: June 25, 2020
    Released: July 11, 2020
    JOURNALS FREE ACCESS

     Science subjects at Japanese high schools are divided into physics, chemistry, biology, and Earth science. The numbers of credits set are two for basic subjects and four for advanced subjects. With a change of courses based on new guidelines enforced by the Ministry of Education, Culture, Sports, Science and Technology Japan (MEXT) in 2012, the Earth science field has classes in Basic Earth Science and Advanced Earth Science. The percentage of high school students who take Earth science classes is estimated from the number of textbooks adopted by MEXT (26% for Basic Earth Science and 1.2-0.9% for Advanced Earth Science), but the percentages of high schools that offer Earth science classes in each prefecture have not been reported. Therefore, the proportion of high schools that offer Basic Earth Science and Advanced Earth Science classes are estimated based on a survey of more than 5,000 high schools in Japan. Data for the survey were collected from the curriculum listed on each high-school homepage and from a questionnaire distributed using the Google mail system. Survey results indicate that 43.7% of high schools nationwide offer Basic Earth Science, and only 8.8% of high schools offer Advanced Earth Science. In addition, the proportion of high schools offering Earth science classes varies depending on the prefecture. The highest proportion of high schools offering Basic Earth Science is 71% (Okinawa) and the lowest is only 4% (Miyazaki). The top prefectural percentage for Advanced Earth Science is 48%, but nine prefectures have no high schools offering Advanced Earth Science. The proportion of high schools offering Earth science correlates with the number of Earth science teachers employed over the past 40 years in each prefecture. However, some prefectures have records only for the total number of science teachers; therefore, the numbers of teachers hired specifically to teach Earth science are not known in these cases. The percentages of high schools offering Earth science classes are higher in prefectures for which only the total number of science teachers is known. A draft is provided on promoting Earth science education at high schools comparing differences among prefectures in the percentages of high schools offering Earth science classes. Based on our results, to promote high school geoscience education, support should be provided through workshops on Earth science education, so that science teachers other than full-time Earth science teachers can recognize the importance of Earth science and teach Basic Earth Science.

    Download PDF (2236K)
  • Masayuki UTSUNOMIYA, Kiyohide MIZUNO, Tomonori NAYA, Kentaro OMURA, Ma ...
    2020 Volume 129 Issue 3 Pages 355-374
    Published: June 25, 2020
    Released: July 11, 2020
    JOURNALS FREE ACCESS

     A tephra bed named CB2038 was found at a depth of 2038.26-2038.21 m in a boring core sample (hereafter called Chiba core) drilled at Chiba City, east of Tokyo Bay. The calcareous nannofossil assemblage from CB2038-bearing siltstone is characterized by the presence of small (< 3 μm) gephyrocapsids and Calcidiscus macintyrei, and the absence of discoasters, suggesting that CB2038-bearing strata correspond to the Ohara to the lower Kiwada formations (lower Pleistocene) exposed on the Boso Peninsula. Possible candidates to be correlative with CB2038 are Oh16A, B in the Ohara Formation, and Kd48.2, Kd48.1, Kd48, and Kd40 in the lowermost Kiwada Formation, because of the similarity of the shapes of glass shards and heavy mineral composition (hornblende > orthopyroxene). Among these tephra beds, Kd48 was considered the best candidate to be correlative with CB2038 based on refractive index, and major and trace element compositions of glass shards. Kd48 identified from deep underground near Tokyo Bay would make a significant contribution to the subsurface stratigraphy of basement strata around the Tokyo metropolitan area.

    Download PDF (5753K)
  • Seiji MARUYAMA, Tohru YAMASHITA, Akira HAYASHIDA, Takafumi HIRATA, Toh ...
    2020 Volume 129 Issue 3 Pages 375-396
    Published: June 25, 2020
    Released: July 11, 2020
    JOURNALS FREE ACCESS

     The Sakate tephra beds in the Chugoku and Kinki districts of Japan have been correlated with the Sambe–Ukinuno (SUk) widespread marker tephras, which were erupted from Sambe volcano (ca. 20 ka). Based on geological surveys of proximal outcrops, the SUk has been divided into three tephras: the lowermost Ukinuno pumice fall deposit (Uk-pfa; normally regarded as the SUk tephra), the Midorigaoka pyroclastic flow deposit (Md-fl), and the uppermost Ukinuno ash fall deposit (Uk-fa). The Sakate tephra has been associated with the Md-fl. Moreover, previous studies have suggested that the refractive index of amphibole in the Md-fl (i.e., Sakate) samples is similar to that in the Uk-pfa samples, whereas those of the volcanic glass shards in the Md-fl samples are lower than those of the Uk-pfa samples. The petrographic properties of Uk-fa suggest that Uk-fa and Md-fl could be treated as a single tephra. However, the SiO2 contents of the Uk-pfa volcanic glasses are slightly higher than those of Md-fl. The FeO contents of the Uk-pfa volcanic glasses are higher than those of Md-fl. This suggests that the difference in the refractive index values of the volcanic glasses is due to the FeO contents rather than the SiO2 contents. A total of 58 elements distinguish the Md-fl volcanic glasses from Uk-pfa, particularly the light rare earth elements, although the trace element patterns are generally similar. This difference may result from fractional crystallization and/or varying magma inputs. In previous studies, the tephras correlated with the Md-fl/Uk-fa (i.e., Sakate) tephras were found to be widely distributed in the Chugoku and Kinki districts. However, those correlated with Uk-pfa were found in the southern Kinki district and immediately offshore, and at the eastern end of Shikoku Island. Uk-pfa and Md-fl/Uk-fa were erupted during the same eruptive sequence, but are clearly distinguishable from each other. The Uk-pfa and Md-fl/Uk-fa tephras can be more simply redefined as the SUk (lower) and (upper) tephras, respectively.

    Download PDF (4219K)
  • Ryo HASEGAWA, Yukio ISOZAKI, Atsushi YAMAMOTO, Yukiyasu TSUTSUMI
    2020 Volume 129 Issue 3 Pages 397-421
    Published: June 25, 2020
    Released: July 11, 2020
    JOURNALS FREE ACCESS
    Supplementary material

     To reconstruct the tectono-sedimentary history of the Cretaceous fore-arc in Japan, U–Pb dating is conducted of detrital zircons in Upper Jurassic and Cretaceous shallow-marine sandstones from the Chichibu belt in Kyushu, Shikoku, and Kii Peninsula, Southwest Japan. The U–Pb ages of detrital zircon in 18 analyzed sandstone samples revealed the following new facts. The predominance of Jurassic grains, with a minor amount of Paleozoic and Precambrian grains, in the Upper Jurassic and pre-Hauterivian Lower Cretaceous sandstones indicates that the fore-arc has been fed with abundant terrigenous clastics from the provenance composed of the Jurassic arc granitoids/accretionary complexes. More Permian grains were supplied probably from the older Permian accretionary complex in a limited way during the Hauterivian, nonetheless, Jurassic grains again dominated in the Aptian sandstones. In contrast, Albian and Upper Cretaceous sandstones are characterized by the remarkable predominance of Cretaceous zircons with almost a complete absence in pre-Cretaceous zircons. This suggests a major reorganization of the arc provenance in the mid-Cretaceous, probably during the Albian; i.e., from the previous regime with dominant Jurassic orogenic elements to a new one solely with Cretaceous arc granitoids. Coeval sandstones in Kanto share the same age spectra and secular changes, indicating not only the monotonous nature of the provenance and fore-arc basin for nearly 1000 km along arc-trench system, but also the appearance of regional tectonism in mid-Cretaceous SW Japan. In particular, the total shut-down of pre-Cretaceous grains into the fore-arc domain probably reflects the appearance of a significant/effective topographic barrier in the arc crust with respect to mid-Cretaceous extensive arc magmatism along the active margin in East Asia, prior to the opening of the Japan Sea in the Paleogene–Miocene.

    Download PDF (5987K)
Short Article
  • Hiroaki NAKAOKA
    2020 Volume 129 Issue 3 Pages 423-442
    Published: June 25, 2020
    Released: July 11, 2020
    JOURNALS FREE ACCESS

     The significance of developing tourist destinations by promoting ecotourism in areas around Tanigawadake in Minakami, Gunma prefecture, Japan, are studied, along with related issues. The aim is to understand the rationale for introducing ecotourism, the reasons why it should be encouraged, and why tourists enjoy ecotourism. The town of Minakami has witnessed a decline in its tourism industry with a decrease in the number of tourists visiting hot springs and ski grounds. Meanwhile, a large concentration of tourists visits the area surrounding Tanigawadake for hiking and trekking. This imbalance is a cause for concern because it can adversely affect the natural environment. To address this, ecotourism has been introduced in the area around Tanigawadake in an attempt to balance environmental conservation with regional development. Ecotours have also been conducted by the Minakami Mountain Guide Association. As a result of the spread of information about the environment, awareness of environmental conservation can be seen in and around the area. It is also observed that tourism workers get a sense of satisfaction from exchanges with tourists and receive income. At the same time, these workers have different expectations about what should be achieved through ecotourism and the role it should play. In particular, a number of workers participating in ecotourism in this area also work in Minakami's tourism industry. They tend to believe that rebuilding the tourism industry in the town is imperative for its growth. However, because the scope of ecotourism was limited to the area around Tanigawadake, efforts focused on this region, limiting the expansion of tourism in Minakami. This was in contrast to the expectations of the workers. Besides, ecotours are positioned as niche travel products. To address this gap, it is important to achieve a balance between tourism and ecotourism by reconsidering local policies and practices, with due consideration given to the actual circumstances of the local tourism industry and the interests of tourism professionals.

    Download PDF (1704K)
feedback
Top