地形
Online ISSN : 2759-2529
Print ISSN : 0389-1755
34 巻, 4 号
選択された号の論文の4件中1~4を表示しています
論説
  • 宇多 高明, 芹沢 真澄, 三波 俊郎, 宮原 志帆
    2013 年 34 巻 4 号 p. 245-268
    発行日: 2013/10/25
    公開日: 2024/12/25
    ジャーナル フリー

    The elongation of a sand spit on a seabed with different water depth and seabed slope was numerically simulated using the BG model (a three-dimensional model for predicting beach changes based on Bagnold’s concept) proposed by Serizawa et al. (2010). The examples of sand spits and a pond enclosed by a barrier were examined first using aerial photographs and bathymetric maps. Then, the formation of a sand spit and a barrier was predicted using the BG model under the conditions that the water depth where a sand spit is formed was changed as 5, 10, 15 and 20 cm in a model scale of 1/100, and that the seabed slope was changed as 1/50, 1/40, 1/30 and 1/20. The difference in the form of a sand spit and a barrier formed under these conditions was explained and compared with the natural sand spits and a barrier.

  • 岡田 操
    2013 年 34 巻 4 号 p. 269-292
    発行日: 2013/10/25
    公開日: 2024/12/25
    ジャーナル フリー

    Peat islets are microtopographical features consisting of islet-shaped accumulations of peat. In this study, the process of formation of these features was investigated with reference to the mountainous bog mires of Hokkaido, Japan. The existence and location of peat islets was confirmed from aerial photos; then, the shapes of the ponds were analysed by photographic measurement and the remnants of sunken ridges were identified by image processing of aerial photographs. The morphological characteristics of mire ponds were also recorded. Additionally, possible mechanisms for the formation of the peat islets were investigated using a computer simulation model that depended upon a mire micro-tope formation model. The results indicated that peat islets always exist in a string-flark complex pattern that is peculiar to bog mires, and that the number of peat islets in a pond increases with increasing shoreline development. Image processing of aerial photos and observation of actual ponds indicated the presence of many sunken ridges. Furthermore, survey results indicated that the ponds do not exhibit uniform depth and that single ponds are often formed by the aggregation of several smaller ponds in the different origin. The submersion of the belt-like peat ridges that previously separated the small ponds has resulted in the fusion of smaller ponds to form larger ponds; then, the sinking of several parts of these ridges could form peat islets. On the other hand, it was recognised that the portion that projected over bog surface from the origin developed into the peat islet individually too.

研究ノート
  • 高屋 康彦, 八反地 剛, 松倉 公憲
    2013 年 34 巻 4 号 p. 293-302
    発行日: 2013/10/25
    公開日: 2024/12/25
    ジャーナル フリー

    To elucidate the effect of polishing process on surface weathering of granite tombstone, laboratory experiments were carried out using a flow-through reactor and an acid solution. Two tablet-type specimens (3.5-cm diameter, 1.0-cm height) polished by three types of processes (#1000 , buff, and Sanwa final) were set in a bottle where HCl aqueous solution of pH 4.5 flows at a rate of ca. 60 mL/day at 25ºC for 56 days, and pH of the output solutions was monitored. Before and after the experiment, surface roughness (Ra) and glossiness (Gs60 ) were measured. Experimental results showed that an increase of Ra and a decrease of Gs60 were less in Sanwa final polishing, i.e. the mirror finish with the minimum rise of temperature and pressure by using a whetstone than that in buff polishing, i.e. the mainstream finish with some stresses by buff polishing. Therefore, it was possible to delay the proceeding of weathering by inhibiting the polishing damage to surface of granite tombstone.

  • Shozo YOKOYAMA
    2013 年 34 巻 4 号 p. 303-312
    発行日: 2013/10/25
    公開日: 2024/12/25
    ジャーナル フリー

    Numerous tors of andesite are found on the somma of Aso caldera, Kyushu, Japan. Many of them are very strongly magnetized as can be detected easily by a geologic compass. Such strongly magnetized rocks, namely lodestones, are presumed to have been formed by the effect of lightning strike. Weathering pits are found on some of the top surfaces of the lodestone tors. According to the recent reports, there are examples of lightning strikes which damaged constructions of granite and concrete. Also, pits on runways formed by lightning strikes have been reported from some airports. Judging from the destructive power of lightning strikes, it is highly probable that pits are formed on rock surfaces by lightning strikes. Thus, it is interpreted, from these, that the weathering pits on the lodestones started from initial depressions formed by lightning strikes.

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