地理学評論 Ser. A
Online ISSN : 2185-1735
Print ISSN : 0016-7444
64 巻 , 11 号
選択された号の論文の4件中1~4を表示しています
  • 野村 亮太郎
    1991 年 64 巻 11 号 p. 735-758
    発行日: 1991/11/01
    公開日: 2008/12/25
    ジャーナル フリー
    広島県北東部,道後山周辺の緩斜面および小起伏面上の地形を火山灰編年学的手法を用いて検討した.この地域の山麓にはI~III面からなる麓屑面,山頂小起伏面上には上位・下位に区分できる岩塊流と高位置扇状地がある.これらの形成年代はテフラと構成層との関係から麓屑面の1面が最終間氷期以前, II1面が最終氷期前半, II2面が同後半, III面と高位置扇状地が晩氷期以降6,000年前頃までの形成であることが明らかとなった. II2面は最終氷期後半の寒冷期に主として凍結破砕による岩屑の生産と,各種のマスムーブメントによる岩屑の下方への移動によって形成され, I面・II1面はそれぞれの寒冷期にII2面と同様の作用によって形成された.III面と高位置扇状地は流水による,より古い堆積物の再移動によって形成された.上位岩塊流は最終氷期前半,下位岩塊流は同後半の寒冷気候環境下で周氷河作用によって形成され,上位・下位諸塊流構成層とII1面・II2面構成層は同時異相の関係にあることが判明した.
    麓屑面は流紋岩地域に最も広く,次いで橄欖岩・花崗岩地域であり,岩塊流は流紋岩と轍横岩地域に分布する.これは岩種による節理密度・風化様式の違いを反映しているとみられる.
    また,本地域と中国山地東部の麓屑面・岩塊流の形成時期はほぼ同時であり,地形形成環境の変動は類似していることがわかった.
  • 貞方 昇
    1991 年 64 巻 11 号 p. 759-778
    発行日: 1991/11/01
    公開日: 2008/12/25
    ジャーナル フリー
    鳥取県弓が浜半島における「外浜」浜堤群の形成に関与した,鉄穴流しに由来するとみられる堆積物の役割を論じた.美保湾に面する「外浜」の地形は,より古い他の二帯の浜堤群(「中浜」,「内浜」)と大きく異なり,低平で堤間低地に乏しく,ほとんど砂丘の発達をみない.また「外浜」の表層堆積物の粒度組成と岩石・鉱物組成は,他の二帯のそれらと比較して著しく粗粒で,花崗岩類起源の岩片・鉱物に富むとともに,鑪製鉄の廃棄物である鋲滓粒を多く含む.地表下10mまでの「外浜」堆積物は,海浜の急速な堆積過程を反映して,深さ約6mまでの粗粒堆積物と,その下の数mの厚さの細粒堆積物に二分される.そのいずれにも鉄津粒を含み,「外浜」の堆積物が鉄穴流しと密接な関係をもつことを裏付ける.火山岩類の割合を指標として,「外浜」と「内浜」両浜堤群の堆積物を比較検討した結果,「外浜」の堆積物中における,鉄穴流しによるとみられる堆積物の割合は,少なくとも,全体のおよそ75%に及ぶものと評価された.また,既存地質柱状図と地区別の面積から得た「外浜」浜堤群の堆積物の全土量のうち, 1.3×108m3が,おもに鉄穴流しに由来するとみられた.この値は,日野川流域における既知の鉄穴流しによる廃土量のおよそ半分近くに相当する.
  • 梅本 亨
    1991 年 64 巻 11 号 p. 779-790
    発行日: 1991/11/01
    公開日: 2008/12/25
    ジャーナル フリー
    Distribution of winter precipitation in Japan was compared for the cases of warm and cold win-ters. In winter, the Japan Sea coast area has a great deal of precipitation brought by the NW mon-soon, whereas the Pacific coast area is dominated by dry weather because the mountains have a “rain shadow” effect against the NW monsoon. Precipitation along the Pacific coast is ordinarily brought by extratropical cyclones passing through off the coast of the Pacific Ocean. Sometimes cyclones emerge in the Japan Sea and bring some precipitation in the area of the Japan Sea coast.
    In cold winters the contrast in distribution of precipitation between the Japan Sea coast and the Pacific coast becomes more marked because of the more persistent and severe NW monsoon. In warm winters, however, such contrast becomes obscure and cyclone precipitation dominates the whole country (Fig. 5).
    Six winters were selected as warm and cold winters from 27 winters (1953/54-1979/80) by the following method. A winter surface temperature (three months: Dec. -Feb.) was represented by nine 10-day mean values. When the 10-day value was higher (lower) than the normal by one standard deviation, it was counted as a warm (cold) 10-day period. The numbers of warm and cold 10-day periods were counted for ten meteorological stations (see Fig. 1-c). The winters that had a large number of warm (cold) periods and a very small number of cold (warm) periods were selected as warm (cold) winters (Fig. 2).
    Figure 4 shows the average precipitation rate and its ratio to normal values for the periods. In a warm winter relatively heavy precipitation (above normal) was observed over a broad area except the Japan Sea coast area, whereas in a cold winter the distribution showed the reverse pattern.
    Synoptic factors bringing precipitation were classified by using daily synoptic charts (Table 1). Figure 6 shows these factors: 1) M-type, in which the pressure patterns are “West-high East-low” type and NW monsoon is strong, 2) L-type, in which extratropical cyclones are situated in the vicinity of Japan and the NW monsoon is very weak or absent, 3) ML-type, which means a transi-tional pattern from L-type to M-type, and 4) 0-type, which means “others” The occurrence fre-quency for the six winters (Table 2) shows that about 70% of total days were classified as days with M- and L-type precipitation.
    Figures 7 and 8 show the precipitation amounts and percentage of total amount for each factor, respectively. M-type precipitation dominated the Japan Sea coast area, especially in the central part of Honshu Island; the percentage value exceeded 50% in cold winters, whereas it was about 20% in warm winters. L-type is the only main factor in the Pacific coast area, so this type showed about 80% in either warm or cold winters. In addition, L-type precipitation is fairly abundant in warm winters even in the Japan Sea coast area, and this became the dominant factor in warm winters almost all over Japan except in the central part of Honshu Island.
    In sum, during warm winters most precipitation in the whole country was caused by extratro-pical cyclones, whereas in cold winters the NW monsoon caused a great deal of much precipitation and dominated in the Japan Sea coast area. The only area with above (below) normal precipitation in cold (warm) winters was the central part of the Japan Sea coast of Honshu, Island, because of the greater increase (decrease) in M-type precipitation than the decrease (increase) in L-type precipitation.
  • 1991 年 64 巻 11 号 p. 791-794,798_1
    発行日: 1991/11/01
    公開日: 2008/12/25
    ジャーナル フリー
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