Journal of Geography (Chigaku Zasshi)
Online ISSN : 1884-0884
Print ISSN : 0022-135X
ISSN-L : 0022-135X
Volume 127 , Issue 3
Showing 1-10 articles out of 10 articles from the selected issue
Cover
  • 2018 Volume 127 Issue 3 Pages Cover03_01-Cover03_02
    Published: June 25, 2018
    Released: August 02, 2018
    JOURNALS FREE ACCESS

     Following the October 2017 activity, Shinmoedake Volcano, located at the center of the Kirishima Volcanic Complex (southern Kyushu), began erupting on March 1, 2018. From March 6, intermittent vulcanian explosions occurred and lava extruded inside the crater. A pancake-shaped lava dome grew and the edge reached the northwestern crater rim on March 9 (foreground in the photo). Subsequently, the March 10 eruption scattered ballistic clasts up to 1.8 km from the crater. Moreover, the March 25 and April 5 vulcanian explosions produced numerous ballistics and small pyroclastic density currents cascading about 400 m down from the crater rim. The May 14 eruption discharged an ash-fall deposit extending to the Pacific coast of Miyazaki prefecture (> 60 km from the vent). In addition, very small eruptions occurred at Ioyama Volcano (about 5 km northwest of Shinmoedake) on April 19 and 26. Takachihonomine Volcano (speculate peak) and Ohachi crater (frequently erupted before 1923 AD) can be seen in the background of the photograph. This aerial photo was taken with the cooperation of the Asahi Shimbun Company.

    (Photograph & Explanation: Yasuo MIYABUCHI; March 9, 2018)

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Original Articles
  • Kei TANAKA, Takashi NAKATA, Ritsuko S. MATSU'URA, Masayoshi TAJIKARA, ...
    2018 Volume 127 Issue 3 Pages 305-323
    Published: June 25, 2018
    Released: August 02, 2018
    JOURNALS FREE ACCESS

    Kambara Jishinyama (earthquake-mound) located on the west bank of lower reach of the Fujikawa river, is widely believed to be a mound that was tectonically formed at the time of the 1854 Ansei Tokai earthquake. Using old maps and aerial photogtaphs, geomorphological changes around Kambara Jishinyama before and after the earthquake are examined. The Fujikawa river frequently flooded and the course on its west bank changed especially after construction of the Karigane-zutsumi (big bank) in order to protect farmland on its east bank. The area around the lower reach of the river was surveyed in 1803 for the Dai Nihon Enkai Yochizu large-scale map, which is the so-called Ino-Daizu. On that map, the river was at almost the same location as its present course. The historical road map (Kaido-Ezu) of Tokaido, which was the trunk road connecting Edo and Kyoto, illustrated in the same period as Ino-Daizu, shows that the Fujikawa river shifted its course close to the foot of river terraces at the west bank. Due to lateral erosion of the river, part of the Tokaido between the towns of Iwabuchi and Kambara collapsed several times. Subsequently, the road was diverted to the new route via Shinzaka as shown on the 1:20,000 scale topographic map published in 1890. A micro-landform classification map of the alluvial lowland of the west bank of the Fujikawa river based on interpretations of aerial photographs taken in 1952 and 1953 reveals that Kambara Jishinyama was located on one of the former mid-channel bars in the braided channels of the river before the 1854 Ansei Tokai earthquake. The earthquake caused a large landslide that dammed the Fujikawa river for a short period at the foot of Shiratori-yama to the north of Iwabuchi. The discharged flood water changed the river course close to the present stream. Geomorphic evidence for tectonic uplift does not exist around Kambara Jishinyama. The Koike river, a small stream flowing in the former main stream of the Fujikawa river, abandoned at the time of the Ansei Tokai earthquake, concordantly flows into the present main stream of the Fujikawa river showing that co-seismic uplift did not take place at the west bank. We conclude that Kambara Jishinyama was not tectonically formed by the earthquake, but is a product of the river course change.

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  • Takayuki MATSUMOTO
    2018 Volume 127 Issue 3 Pages 325-341
    Published: June 25, 2018
    Released: August 02, 2018
    JOURNALS FREE ACCESS

     Previously a mystery, era in which the Ashidani Formation was formed in the Hida Gaien Belt at Kuzuryu is determined. The detrital zircon SHRIMP U–Pb age of Ashidani Formation sandstone is found to be within the range of 280 and 220 Ma. The most recent generation noted in samples collected is 224.2 ± 5.4 Ma (between the Carnian and Norian stages of the late Triassic Period). The metamorphic muscovite K–Ar age of sandstone schist is 182.6 ± 3.9 Ma (between the Pliensbachian and Toarcian stages of the Early Jurassic Age). There are no previous reports on metamorphic age values of 180 Ma in the Hida Gaien Belt. According to these dating results, geological development of the Ashidani Formation was limited to between the latter part of the late Triassic period and the start of the early Jurassic period, and can be compared to the Chizu metamorphic belt in the Chugoku region. Geological development of the Ashidani Formation is limited to the start of the early Jurassic period. Ashidani Formation Rocks were deposited in the forearc region of the eastern margin of the China craton at the beginning of the early Jurassic period. They then underwent high-pressure metamorphism alongside protoliths of the Chizu metamorphic belt in the middle part of the early Jurassic period due to subduction of the oceanic plate.

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Short Article
  • Madoka UEMURA
    2018 Volume 127 Issue 3 Pages 343-356
    Published: June 25, 2018
    Released: August 02, 2018
    JOURNALS FREE ACCESS

     The purpose of this study is to show how retired workers are supported in Toyota city, Aichi prefecture to engage in agriculture, and the significance of that support. Toyota city is renowned for its automobile industry. During the period of rapid economic growth, the automobile industry attracted many workers from inside and outside Toyota city. However, since around 2000, when many workers started to reach retirement age, the issue of how to help them find a place in the community outside their companies has been a challenge. Toyota city also faces the challenge of how to respond to a declining number of people engaged in agriculture. To address both of these problems, in collaboration with the Japan Agricultural Cooperative (JA), Toyota city established the Agricultural Lifestyle Support Center, where retired workers can learn agricultural skills. The Center helps retired workers transition smoothly from corporate life to agricultural life by providing guidance and information on available farmland, as well as leasing agricultural equipment. Toyota city and JA also help develop sales channels for produce grown by retired workers.In Toyota city, retired workers from other areas who have no farmland to cultivate are also regarded as prospective farmers in the same way as retired workers who were originally from the local area and who own farmland. Support is provided equally to both categories of retiree. It is reasonable to say, therefore, that these support measures are significant in that they help prevent farmland from being abandoned with the help of retired workers, who are also supported as prospective farmers. Consequently, creating a place where farming skills can be taught and support can be provided for marketing the resulting produce is important for both retired workers and the local community.

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Special Issue: Liquefaction Phenomena in the Downstream Basin of the Tone River, Eastern Kanto Region, Japan from the Viewpoint of Earth Science
Original Article
  • Taku KOMATSUBARA, Kiyohide MIZUNO, Masaru SAITO, Takashi HOSOYA, Atsus ...
    2018 Volume 127 Issue 3 Pages 361-389
    Published: June 25, 2018
    Released: August 02, 2018
    JOURNALS FREE ACCESS

     The 2011 off the Pacific coast of the Tohoku earthquake caused severe liquefaction events in the Kanto region, which is 300-400 km south of the earthquake's epicenter. All-core drillings and trenching surveys were carried out at Yodaura and Mukoya, which are situated in the lowland along the lower Tone River in the central Kanto region. The Yodaura site is on reclaimed land where a former lake was filled in by sand pumping from 1969 to 1974. The sediments at Yodaura consisted of silts and clays of the former Lake Yodaura deposits (natural sediments) and sandy strata composed of artificial fill. No evidence was found of liquefaction in the natural deposits, but the artificial-fill deposits suffered severe liquefaction. Three distinct sand dikes (yS1 sand dyke–yS3 sand dyke) cut the artificial strata at Yodaura: yS1 sand dyke, composed of gray, unoxidized sand, reached the ground surface and cut yS2 sand dyke, which was composed of light-brown, oxidized sand. Therefore, two liquefaction events occurred at the same point: the older event, which produced yS2 sand dyke, was probably induced by the 1987 off the east coast of Chiba Prefecture earthquake (Mj = 6.7), and the newer one, which produced yS1 sand dyke, was induced by the 2011 earthquake. The third sand dike (yS3 sand dyke) originated in a bed of fine to medium sand containing shell fragments in the artificial strata and contained fragments of asphalt from the ground surface. This dike is consistent with eyewitness accounts of sand gushing during the 2011 event. These accounts report that the ground pulsated at intervals of several seconds, and water and sand spouted from the ground simultaneously with each ground motion pulse. The presence at Yodaura of massive un-stratified sand beds within well-stratified sandy layers, especially near the sand dikes, indicates that liquefaction destroyed the original structure of the sediments. The Mukoya site is on reclaimed land where an abandoned channel of the Tone River was artificially filled in after 1956 by sand pumping and sediment dredging. The surface sediments at the Mukoya site are composed of Holocene floodplain deposits, abandoned channel sediments deposited between 1626 and 1956, and artificial strata. Two distinct deformation structures (mS1 and mS2) were observed in a trench wall. mS1 was a sand dyke that originated in the upper member of the abandoned channel sediments and reached the ground surface. The mS1 sand dyke consisted of liquefied materials derived from the dredged fine to medium sand deposits of the lower part of the artificial strata, and where it was ejected, a “shoulder-like” point formed on the upper surface of the sandy dredged deposits. Structure mS2 was a depression structure in the lower part of the artificial strata that displaced the sandy dredged deposits and an underlying buried soil layer downward. A “sill-like” horizontal sand dike extended from the sandy deposits into the buried soil. In the muddy upper part of the artificial strata, there were many fractures parallel to sand dyke mS1 and the “shoulder” of the sandy dredged deposits. The presence of these fractures indicates that minor subsurface geological structures affected the ground motion and location of liquefied sites caused by the earthquake.

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Letters
  • Masaru SAITO, Takashi HOSOYA, Osamu KAZAOKA, Kiyohide MIZUNO, Mitsuo S ...
    2018 Volume 127 Issue 3 Pages 391-407
    Published: June 25, 2018
    Released: August 02, 2018
    JOURNALS FREE ACCESS

     Trenching surveys (excavating a ground surface and observing the exposed strata) are methods for immediately comprehending shallow subsurface stratigraphy, geological structure, and properties of strata. The most suitable survey method is presented for observing liquefied and fluidized strata under the ground, and for considering liquefaction countermeasures in an alluvial lowland where man-made strata are sporadically distributed and the groundwater table is generally shallow. Also presented is an outline of the procedure. To narrow the trench site, it is essential to analyze topographical data, historical record of liquefaction, and subsurface geology based on drilling data and groundwater table. Prior to excavating, sheet piles are driven and tightly arranged around the site. Then, riser pipes and a centrifugal pump are set into the trenching area to lower the groundwater level (the well-point method). During the process of dewatering and discharging water, environmental influences on surrounding areas should be considered. The depth of a trench in practice is 3 to 4 m or less. If it is necessary to obtain deeper strata, long specimens oriented via special sheet pile tool sampling can be used. After making observations of stratigraphy and structure of normal layers or liquefied and fluidized layers exposed on trench walls, it is useful to make relief peel specimens with a grout material to describe detailed liquefaction and fluidization features. It is proposed that exhibiting peel specimens is effective for understanding liquefaction and fluidization processes. Samples of liquefied strata for some examinations can be collected directly from trench walls.

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  • Mamoru KOARAI, Takayuki NAKANO, Hiroshi UNE
    2018 Volume 127 Issue 3 Pages 409-422
    Published: June 25, 2018
    Released: August 02, 2018
    JOURNALS FREE ACCESS

     Many instances of liquefaction occurred throughout the lowlands of the Kanto Plain, central Japan following the 2011 off the Pacific coast of Tohoku Earthquake. In particular, serious liquefaction damage was concentrated at reclaimed land, such as at former river channels and lakes. This indicates the importance of referring to landform classification when making a liquefaction risk assessment. And, predictions of liquefaction risk should be based mainly on landform classification data. Liquefaction damage varies widely with differences in shallow geological conditions, even within the same landform classification. Liquefaction risk is assessed based on a finer micro landform classification created by adding forms calculated from DEM or by adding boring database sets. In addition, artificial modifications occurring within a short period, such as backfilling a site where gravel was removed, often affect liquefaction phenomena, and it is important to refer frequently to the history of an area.

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Review Article
  • Hiroshi UNE, Taku KOMATSUBARA, Yoshinori MIYACHI, Takayuki NAKANO
    2018 Volume 127 Issue 3 Pages 423-438
    Published: June 25, 2018
    Released: August 02, 2018
    JOURNALS FREE ACCESS

     The distribution of liquefied areas in the lower basin of the Tone River caused by the 2011 off the Pacific coast of Tohoku Earthquake does not correspond to the results of liquefaction assessments applying conventional geotechnical approaches. Papers in two special issues titled “Liquefaction Phenomena in the Downstream Basin of the Tone River, Eastern Kanto Region from the Viewpoint of Earth Science” clarify that the earth scientific approach focusing into micro-landforms, extremely shallow geology, and land development processes can provide much important information for liquefaction assessments. The results of the survey on the present situation of liquefaction hazard maps published by municipalities reveal many problems in terms of contents and expressions. It is proposed to create an appropriate manual for assessing liquefaction risk and producing liquefaction hazard maps of municipalities.

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