地形
Online ISSN : 2759-2529
Print ISSN : 0389-1755
34 巻, 2 号
選択された号の論文の3件中1~3を表示しています
論説
  • 梅田 美彦
    2013 年 34 巻 2 号 p. 113-128
    発行日: 2013/04/25
    公開日: 2024/12/25
    ジャーナル フリー

    Some field surveys of marshes around Tajimi, Japan, were carried out to determine the origin of the spring-water marshes distributed in the Tono area of Gifu prefecture. Microtopography, geological features, soil, and groundwater around the marshes were investigated. It became clear that the marshes are on different geomorphic surfaces, such as upper and lower side-hollows, terraces, channelways, and bottomlands. Terraces were formed around the boundary between the Toki gravel formation and the basement stratum, and they were made by the collapse of the gravel bed. The marshes located on terrace surfaces are the most upper part marshes in the valley. Other marshes were formed on the down-stream side of the terraces. This area received the block movement after the Tertiary Period, and was divided into many parts. The basement stratum was located to the various altitudes, and the marshes were formed above various sea levels. The marshes’ formation started after MIS (Marine isotope stage) 3, in terms of the age of terrace formations around the Toki River.

研究ノート
  • 今泉 文寿, Roy C SIDLE, 外狩 麻子, 島村 誠
    2013 年 34 巻 2 号 p. 129-146
    発行日: 2013/04/25
    公開日: 2024/12/25
    ジャーナル フリー

    Rate of sediment infilling into landslide scars by soil creep is needed to estimate the timing of subsequent landslide activity at a particular site. However, knowledge about the spatial distribution of its activity around the landslide scar is scarce. Additionally, there are few studies on the temporal changes in the soil creep activity in relatively longer periods (i.e., more than several years). At a study site in central Japan, we monitored the spatial distribution and temporal changes in soil creep activity in and around the Kumanodaira landslide by using strain probes and fixed-point surveys of markers. Our observation results showed that soil creep was active above the head scarp of the landslide, whereas soil creep was relatively inactive around the sides of the landslide. Soil creep activity is poorly correlated with the frequency of freeze-thaw as well as rainfall attributes. Soil creep mainly contributes to infilling of the landslide scar via sediment inputs from the slope above the head scarp rather than along the flanks of the landslide.

  • 井上 信, 田中 靖
    2013 年 34 巻 2 号 p. 147-166
    発行日: 2013/04/25
    公開日: 2024/12/25
    ジャーナル フリー

    We developed versatility- and simplicity-conscious landscape evolution models (LEMs) and applied them to actual topography in Japan to predict topographic change. The development of LEMs requires that geomorphic transport laws (GTLs) express uplift/subsidence, river erosion, mass movement on slopes, and sea erosion. We reviewed previous studies on LEMs and in related fields, and selected those GTLs most suitable to the aim of this study and incorporated them into the LEMs. We applied the LEMs to the actual topography in a Japanese coastal area and simulated the topographic changes that would occur during two glacial–interglacial cycles. The LEMs reproduced some theoretically predicted topographic changes, such as the formation of marine terraces by uplift, changes in drainage, and generation of a drainage network. We examined the influence on topographic changes of differences in coefficients and parameters related to river and sea erosion. As drainage indexes became larger, channels meandered more and the drainage network increased in complexity. The result is consistent with previous research. However, marine terraces seemed to form earlier under conditions of a faster uplift rate or a gentler angle of the seabed. This means that the formation age of a paleo-shoreline should depend on the specific site conditions of its location in the general area. Differences in formation age also lead to differences in the formation elevation of the paleo-shoreline. The result is inconsistent with the traditional interpretation of Japanese geomorphologists that the formation age and elevation of the paleo-shoreline must be homogeneous across an area in order to discuss whether a phenomenon actually occurs or not, or to what extent. We require more advanced LEMs based on investigations of actual topography and geology, observations of actual topographic changes, theory construction, and technical development.

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