地学雑誌
Online ISSN : 1884-0884
Print ISSN : 0022-135X
ISSN-L : 0022-135X
128 巻 , 6 号
選択された号の論文の9件中1~9を表示しています
表紙
  • 2019 年 128 巻 6 号 p. Cover06_01-Cover06_02
    発行日: 2019/12/25
    公開日: 2020/01/28
    ジャーナル フリー

     赤銅色をした,太古代のグラノファイアーの岩塊が写真の丘をつくっている.丘頂高度は約30 mで,南緯20.6°,西オーストラリア州・ダンピア(バーラップ半島,ピルバラ地区)に位置する.この一帯の気候は,約8 km離れたカラサでの観測によると最高気温は48.2°Cに達し,年降水量297 mmと砂漠のようである.岩塊は節理に沿って割れ,生産されたのであろう.いずれも角張っており,大きいもので長径2 m程度である.岩塊の色は,表面に発達する砂漠ワニスに起因する.先住民アボリジニは,その表面を削って人,動物,幾何学模様などオーストラリアでもっとも多くの岩絵を残した.このため,考古学的に重要な場所を含む土地は,ムルジュガ国立公園に指定され保護されている.

    (写真・説明:藁谷哲也 2019年3月20日撮影)

論説
  • 南雲 直子, 江頭 進治
    2019 年 128 巻 6 号 p. 835-854
    発行日: 2019/12/25
    公開日: 2020/01/28
    ジャーナル フリー

     A detailed description is presented of hazards that caused the 2017 Akatani River flood disaster, which affected a large area from mountains through lowlands. Hazards are analyzed focusing on sediment transport, fluvial topography, and characteristics of house damage. Based on field surveys and aerial photograph interpretation, lowlands are classified into alluvial fans, colluvial slopes, terraces (I, II, and III), valley plains (I and II) and former channels, and fill and cut land. A number of slope failures occurred on mountain slopes of more than 30 degrees, and debris flows reached areas with slopes of 4 to 8 degrees. Alluvial fans formed in tributary valley mouths overlaying former alluvial fan surfaces, indicating recurrences of debris flows. Sediment and driftwood carried by debris flows were transported further downstream by floodwater, and heavy inundation was observable in areas downstream from debris flow deposits. This inundation mainly occurred in valley plains I and II, and was accelerated by channel deformation caused by sediment accumulating with driftwood. Calculations reveal that the sediment transport capacity of the Otoishi River was higher than that of the upper Akatani River; thus, sediment and driftwood from the Otoishi River were actively transported downstream and flooded the lower Akatani River. Through all of these processes, longitudinal sediment fining detected over the lowlands was notable, and only suspended loads flooded the lowest portion of the basin. An investigation of house damage types and their locations shows that more than 53% of houses in the study area were damaged by hazards, consisting of 36% by the flood and 17% by slope failures and debris flows. The investigation also finds a close relationship between the number of damaged houses and topographic surfaces; most of the houses damaged by the flood were located in valley plains, and most of the houses damaged by slope failures and debris flows were observed in alluvial fans. In addition, most of the flood-affected houses were located quite close to main channels, within 10 to 30 m from the channels and 2 to 5 m above the water surface.

  • 梶田 真
    2019 年 128 巻 6 号 p. 855-878
    発行日: 2019/12/25
    公開日: 2020/01/28
    ジャーナル フリー

     Demographics in Tokyo between 1920 and 1965 could not be clarified because of a severe social crisis resulting from two significant disasters—the Great Tokyo Earthquake and the Great Tokyo Air Raid—as well as by subsequent land re-zoning projects and residential address reorganization policies, such as Chomei Chiban Seiri and Jyukyo Hyoji. This missing period is addressed by scrutinizing comparability between cho-scale tabulations of different censuses carried out in this timeframe and visualizing changes in comparable districts. The findings are summarized as follows.

    (1) Areas within about 5 km from central Tokyo, which could be covered by foot, were already fully urbanized by 1908. Areas more than 5 km from central Tokyo became urbanized with the development of streetcar lines after the 1910s.

    (2) There were only small differences in the socio-spatial structure between areas within 5 km of central Tokyo in 1920 and those in 1965. Nevertheless, small and medium-size factory and blue-collar areas in the western valley region diverged. Although northwestern valley areas continued to have a predominant demography of laborers working in small and medium-sized factories, they rapidly disappeared in southwestern valley areas. The main reason for this contrast is that the former continued to be competitive in the core industry of printing and publishing.

    (3) In contrast to concentric spatial patterns of familial characteristics after the 1970s, those in 1920 showed clear distinctions between outer-eastern and outer-western Tokyo. This change was led by a labor force recomposition of the former after WWII. Before the war, outer-eastern Tokyo was made up of industrial areas whose labor forces were occupied by middle-aged workers with families and children. After the war, its core labor force was replaced by young singles moving in from surrounding and non-metropolitan areas.

  • 丸山 誠史, 竹村 恵二, 平田 岳史, 山下 透, 檀原 徹
    2019 年 128 巻 6 号 p. 879-903
    発行日: 2019/12/25
    公開日: 2020/01/28
    ジャーナル フリー

     本論文では,水月湖から掘削された2つのコア試料(SG93およびSG06)に含まれる可視テフラ層の,岩石学的特性に関して報告する。水月湖のテフラ層に含まれる鉱物や火山ガラスの屈折率,火山ガラスの形状,鉱物構成のような,基本的かつ重要な岩石学的特性は,これまで公表されてこなかった。水月湖コア試料のテフラ層は,九州のカルデラ(例えば阿蘇,阿多,姶良)を起源とするものと,西南日本の中国地方に存在する大山および三瓶火山を起源とするものに大別することができる。水月湖コア試料には,日本海上の鬱陵島を給源とする鬱陵–隠岐テフラ,三瓶浮布テフラと密接な関係がある阪手テフラ,そして給源火山が不明なスコリア層も存在していた。日本海で掘削されたコア試料から見いだされた山陰1テフラに対比された,水月湖コア試料のテフラ層は,岩石学的特性に基づくと,九州の九重カルデラから噴出した九重第1テフラとも対比可能である。岩石学的特性の記載はテフラ層の識別・対比に関して,火山ガラスの主要元素組成だけでは得ることのできない重要な制約条件を与える。しかしながら,いくつかのテフラ層の対比はいまだ曖昧さを残しており,種々の微量元素組成も含む火山ガラスの地球化学的データも,識別・対比をより厳密に行うために必要である。

短報
  • 秋山 大地, 須貝 俊彦, 岡崎 浩子, 中里 裕臣, 大井 信三
    2019 年 128 巻 6 号 p. 905-920
    発行日: 2019/12/25
    公開日: 2020/01/28
    ジャーナル フリー

     Marine and fluvial terraces in the Kanto Plain mostly formed in marine oxygen isotope stage (MIS) 5 under the concurrent influence of eustatic sea-level changes and Kanto basin-forming movements. In the central part of the plain, however, it remains unknown when and how terraces composed of the upper Pleistocene Joso and Kioroshi Formations, Shimosa Group developed. Terrace surfaces are classified by integrating geomorphic, sedimentary facies, and tephra analyses focusing on the southern Sashima and Tsukuba Uplands, including the northwestern Shimosa Upland. Terrace surfaces are classified into levels I to III. Terrace sediments distributed over levels I to II from the top in the Sashima, Tsukuba, and Shimosa Uplands are divided into two formations: Kioroshi Formation composed of beach facies and Joso Formation composed of flood plain and fluvial channel facies.Found in the Joso Formation were tuffaceous silt layer and pumiceous sand layer, including tephra grain correlated with On-Pm1 (c. 96 ka: Aoki et al., 2008) and Nk-Ma (c. 100 ka: Yamamoto, 2012) in the southern Sashima and Tsukuba Uplands, which allow fluvial terraces formed in the Central Kanto Plain after MIS 5c to be identified.

  • ─欧米系ツーリストの来訪動機に着目して─
    市川 康夫
    2019 年 128 巻 6 号 p. 921-940
    発行日: 2019/12/25
    公開日: 2020/01/28
    ジャーナル フリー

     Inbound walking tourism at the Nakasendo-route post towns of Tsumago-juku and Magome-juku is investigated to clarify the format and the context of the walking tourism experience from the motivation of visiting Western tourists. A questionnaire survey was carried out in a case study on the Nakasendo-route (Kisoji) between Tsumago-juku and Magome-juku. The results of the survey reveal the following. Western tourists visit the Nakasendo route hoping for a “different tourist experience,” not “something found in inbound tourist guidebooks.” They seek “quiet,” “calm,” and an “escape from metropolises (non-urban areas)” as well. Japan's urbanized sightseeing exhausts them, and they seek out the Nakasendo route hoping for a peaceful and quiet communion with nature. They hold in high regard the natural landscape of “mountain ranges,” “forests,” and “rivers and waterfalls,” as well as “rice paddies,” “agricultural scenes,” and a “rural lifestyle,” that may be considered “ordinary” by Japanese people living in agricultural regions. Overall, Western tourists do appreciate an “authentic rural experience,” and the elements of ancient Japanese history and culture that can be seen even in the present day. Moreover, Western tourists who visit the Nakasendo are typically employed in knowledge-based professions, working as lawyers, doctors, researchers, and professors, or in creative professions, working as designers, architects, or IT professionals. As a result, it can be concluded that walking tourism in the Nakasendo appeals to Western tourists who seek an alternative tourist experience of peace amidst nature, which is not available in a city, both because the Nakasendo is not frequented by Western tourists and because it offers something different from a “typical” sightseeing experience.

寄書
  • ─室蘭市絵鞆半島の外海岸急崖の産状─
    山岸 宏光, 畑本 雅彦, 鎌田 光也, 志村 一夫
    2019 年 128 巻 6 号 p. 941-952
    発行日: 2019/12/25
    公開日: 2020/01/28
    ジャーナル フリー

     “Buratamori Muroran,” an NHK Japan TV program was broadcasted on November 25, 2017. To prepare for the program, observations were made on the Etomo Peninsula using ortho-photographs provided by Muroran City as Open Data. A large number of aerial photographs were taken using aircrafts and observational research was undertaken by road. In addition, cliffs were observed from a small boat provided by Hokkaido Regional Development Bureau, Muroran. As a result of these research activities, many remarkable outcrops and occurrences of Miocene subaqueous volcanic rocks were observed on the cliffs, most of which are inaccessible. Subaqueous pumice flows, concentric and radial columnar jointed dikes called Peach Rock, subaqueous lava domes associated with hyaloclastites, and their feeder dikes forming apophyseal, polygonal and columnar-joints were observed. The occurrences of these variable subaqueous volcanic rocks are described and models of some volcanic rocks are described. Finally, cliffs are defined as subjects for geo-tourism.

  • ─写真と図で見るローヌ氷河とローヌ湖の変貌─
    小元 久仁夫
    2019 年 128 巻 6 号 p. 953-958
    発行日: 2019/12/25
    公開日: 2020/01/28
    ジャーナル フリー

     The well-known Rhone glacier in the Alps is showing a spectacular and rapid retreat. A pro-glacial lake appeared in front of it in 2006. Called Rhonesee, it is gradually increasing in size and extent. Several photographs taken on June 28, 2018 show the retreat of the Rhone glacier and the extended features of the pro-glacial lake. It is considered that the glacier will continue to retreat in the future, and the extending Rhonesee could separate into large and small lakes.

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