地形
Online ISSN : 2759-2529
Print ISSN : 0389-1755
36 巻, 3 号
選択された号の論文の6件中1~6を表示しています
特集:九州沖縄の地形学-九州沖縄における地形研究者のネットワーク構築を視野に入れて-
  • 鹿島 薫, 黒木 貴一, 菅 浩伸, 大貫 靖浩, 永迫 俊郎
    2015 年 36 巻 3 号 p. 139-140
    発行日: 2015/07/24
    公開日: 2024/12/25
    ジャーナル フリー
  • 長岡 信治, 奥野 充
    原稿種別: 研究論文
    2015 年 36 巻 3 号 p. 141-158
    発行日: 2015/07/24
    公開日: 2024/12/25
    ジャーナル フリー

    The Kuju Volcanic Group consists of over twenty lava domes and small stratovolcanoes. It has effused 22.3 km3 of magma, consisting of lavas (15.5 km3), pyroclastic flows/surges and debris avalanches (4.4 km3 and fallout tephra (2.5 km3). The average magma discharge rate is 0.15 km3/ky. Most lavas formed hornblende andesitic and dacitic lava domes except for the Hiijidake which is a basaltic stratovolcano. Based on eruption types and rate, the eruptive history of the Kuju Volcanic Group can be divided into four stages: K1, K2, K3 and K4. The K1 stage (150 to 110 ka) is characterized by hornblende dacitic ignimbrite eruptions that formed the Miyagi and Shimosakata ignimbrite. The activity of K2 stage (110 ka to 60 ka) occurred in the western part of the group. More than eight lava domes of two-pyroxene hornblende andesite were formed, some with associated explosive activities that generated sub-plinian eruptions forming Hotokenoharu pumice-fall and Miyakono scoria-fall deposits. The K3 (ca. 54 kBP) is the most catastrophic and voluminous eruptive stage. The stage began with Kuju D ash-falls. Large-scale plinian eruptions formed the Kj-P1 pumice-fall deposit with a volume of 6.2 km3. During the plinian eruptions, the northern and southern portions of the eruption column collapsed, and generated the Handa ignimbrite. The Handa ignimbrite attained a volume of 5 km3. Some parts of the Kj-P1 pumice-fallout deposit were deposited atop the Handa ignimbrite, which makes this eruption a typical intraplinian type with a DRE volume of approximately 4.1 km3. A small-scale caldera might be formed during the K1 and K3 stages. The K4, a post-caldera stage can be divided into three sub-stages. During 49 cal kBP to 35 cal kBP, Hosshozan and Ogigahana hornblende-andesite domes emerged, and Kan’nojigoku and Shirani block-and-ash flow deposits had originated from them. Sub-plinian eruptions at Shirakuchidake volcano formed Itakiri lapilli fallout. The period during 32 to 7.3 cal kBP emplaced various magmas of basaltic to dacitic composition. A basaltic activity in this sub-stage formed Hiijidake stratovolcano (lava flows, Nagayu and Hiijidake scoria-fallouts and debris avalanches). During this period, many lava domes were also formed such as Hizengajo, Kujusan, Dainoyama, Mimatayama and Inaboshiyama volcanoes. Sector collapse of Kujusan and Dainoyama lava domes produced the Azamidai and Dainoyama block-andash flow deposits, respectively. Mimatayama eruption started with phreatomagmatic eruption forming Sugamorigoe pyroclastic surges. This is followed by the growth of the Older Mimatayama lava dome with the associated Sugamorigoe block-and-ash flows. The lava domes collapsed generating the Matsunodai debris avalanches. After the collapse, Younger Mimatayama lava domes grew inside the horseshoe shaped crater. After 7.3 cal kBP, the eruption centers moved to the east and the magma rate increased from 0.07 km3/ky to 0.51 km3/ky. The large andesite to dacitic lava domes of Yuzawayama, Tacchusan, Taisenzan, Kurodake were formed. Taisenzan is a complex andesitic stratovolcano. Later vulcanian eruptions formed Danbaru crater and Kj-A1 ash falls. The sub-plinian eruption deposited the Danbaru scoria-fallout. The vulcanian and sub-plinian eruptions generated the Komekubo ash and scoria fallout. The largest eruption at 1.6 cal kBP formed the Kurodake lava dome with a volume of 1.6 km3.

  • 中西 利典, 竹村 恵二, 松山 尚典, 齋藤 武士, 柴田 康行, 香月 興太
    原稿種別: 研究論文
    2015 年 36 巻 3 号 p. 159-172
    発行日: 2015/07/24
    公開日: 2024/12/25
    ジャーナル フリー

    Sedimentary facies, diatom assemblages and radiocarbon ages of two drilling cores were determined to estimate the Holocene activity of the Asamigawa fault at Hamawaki area in Beppu city, western Japan. Based on these analyses, artificial soil, fluvial sediment, marsh to shallow marine sediment, middle-Pleistocene Otobaru lava were identified from top to bottom. The vertical offset of Kikai-Akahoya volcanic ash at the subsidence side of the fault indicates that the vertical slip rate was at least 1.4 mm/yr since 7300 cal BP. The last faulting event might have been after 600 cal BP because the floodplain sediment was observed at 3-4 m below the present sea-level.

  • 釣田 竜也, 大貫 靖浩, 壁谷 直記
    原稿種別: 研究論文
    2015 年 36 巻 3 号 p. 173-194
    発行日: 2015/07/24
    公開日: 2024/12/25
    ジャーナル フリー

    We traced the changes of water chemistry from soil to stream at the Kahoku experimental watershed No.3 (KHK-3) in northern Kyushu. Preferential flow reflecting water chemistry of A0 leachate was collected in the topsoil compared with in the subsoil. It was suggested that intensive summer rainfall and water repellency at surface soil had contributed to the generation of preferential flow. In spite of the emergence of preferential flow in the soil profile, seasonality of the groundwater, spring water and stream water chemistry indicated that KHK-3 is the watershed where the predominant hydrological pathway is the matrix flow from the saturated groundwater zone. At the KHK-3, saturated zone is so small because of shallow soil and saprolite thickness that groundwater chemistory is easy to change, which directly affects the seasonality of the stream water chemistry.

  • Naoki KABEYA, Akira SHIMIZU, Takanori SHIMIZU, Hitoshi IKUZAWA, Hirosh ...
    原稿種別: research-article
    2015 年 36 巻 3 号 p. 195-204
    発行日: 2015/07/24
    公開日: 2024/12/25
    ジャーナル フリー

    The Chibana No. 1 catchment, which consists of a Pinus luchuensis afforestation area, was installed to understand the hydrological environment of the northern forest on Okinawa Island. An interception plot (5 m × 8 m, stand density 2,000 trees/ha) was installed in this catchment. Interception loss was calculated from observational data collected in this plot in 2010 and 2011. In 2010, an abnormally elevated rainfall total of 3,403.6 mm was observed, while 2011 saw an average rainfall of 2,387.0 mm. The interception losses in 2010 and 2011 were similar, 18.1 and 19.3%, respectively. These losses were lower than the 27.5% interception loss reported for the Minami-Meijiyama catchment (stand density 5,278 trees/ha) that comprises secondary, natural broadleaf trees in the central part of Okinawa Island. It is thought that these differences mainly resulted from the differences in stand densities.

  • 黒木 貴一, 磯 望, 後藤 健介, 黒田 圭介, 宗 建郎
    2015 年 36 巻 3 号 p. 205-213
    発行日: 2015/07/25
    公開日: 2024/12/25
    ジャーナル フリー

    In this study, the relationship between vegetation recovery and soil development during 26 years is discussed which was developed inside of a landslide scar, caused after the 1982 Nagasaki Heavy Rainfall Disaster. A terrain model of the survey area in the landslide scar was made by handy measurements. We set dense points in the scar and measured soil thickness, diameter of tree trunks and location of each point, to make distribution maps of these factors. We clarified the relation between the soil thickness and slope gradient, the tree locations and soil thickness, and terrain distribution and other measured factors, by overlay analysis. The landform of the area shows step-like surface consisted of gentle and steep slopes reflecting the subsurface shape of basement rock and the soil thickness. The soil thickness increases downward on the gentle slope and decreases downward on the steep slope. The number of trees and the diameter of trunks are larger in the thick soil covered area or those area that soil thickness decreases downward. After the landslide occurrence, soil layer development starts from where the downward moving of weathered materials and plant litters are intercepted by the convex part of the basement rock. Then, the soil layer seems to be gradually thicker where their downward moving is intercepted by the growing tree. The average speed of the soil layer development is concerned approximately 0.19cm per year. In the case of this speed, the return period to develop the thickness of soil layer that becomes easy to collapse is estimated to be approximately 158 years on average, and up to approximately 263 years.

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