地形
Online ISSN : 2759-2529
Print ISSN : 0389-1755
34 巻, 1 号
選択された号の論文の4件中1~4を表示しています
論文
  • 吉田 英嗣
    2013 年 34 巻 1 号 p. 1-19
    発行日: 2013/01/25
    公開日: 2024/12/25
    ジャーナル フリー

    This research discusses the volumetric magnitude of the catastrophic sector-collapse of Bandai volcano occurred in the late Pleistocene. The collapse produced the hugescale rockslide-debris avalanche deposits named as the Okinajima debris avalanche. The collapse had occurred at the southwestern part of the volcano, and the Okinajima debris avalanche rushed down into the Inawashiro and the Aizu basins and deposited there. Along with the conspicuous hummocky landforms observed now, we can recognize the remnant topography of horseshoe caldera on the southwestern sector of volcanic edifice. Some previous researches indicate that the collapse volume (or depositional volume) reaches 4 cubic kilometer (km3) or more. In regard to the catastrophic collapse volume at the Bandai volcano, the author has once examined another event occurred in 1888 A.D., the smaller one. By focusing on the size-distance distribution pattern of debris avalanche hummocks, it is evaluated the appropriateness for the volume estimation of the 1888 collapse as ca. 0.49 km3 which is the value estimated by the previous study. Based on this implication, in the present research, the author offers new insights that the collapse volume is significantly smaller than 4 km3 once estimated as; collapse volume is not likely to exceed beyond ca. 3.2 km3, calculated from the dimensions of the volcanic body and the source area; scar size is approximately five times larger than that of the 1888 collapse, which amounts to the collapse volume of the Okinajima event of ca. 2.5 km3 at a maximum, referred to ca. 0.5 km3 of the 1888 event; according to the empirical relationship proposed by the author’s previous results and the distribution pattern of the Okinajima’s hummocks, the loss volume by the collapse is expected as ca. 2.0 km3. In conclusion, the loss volume of the southern volcanic edifice due to the Pleistocene catastrophic collapse should be a half of the value previously considered.

研究ノート
  • 早川 裕弌, 松多 信尚, 前門 晃, 松倉 公憲
    2013 年 34 巻 1 号 p. 21-36
    発行日: 2013/01/25
    公開日: 2024/12/25
    ジャーナル フリー

    Recession rates of four waterfalls formed by the surface deformation of the Chelungpu Fault at the time of Chi-Chi Earthquake on September 21, 1999 in central Taiwan were measured in the field and assessed with an empirical model of waterfall erosion. The model represents the balance between the erosive force of streams versus bedrock resistance with relevant environmental parameters of discharge (drainage area and precipitation), waterfall form and bedrock strength. The recession rates of three waterfalls increased from the first 6 years to the following 4 years. This increase in the recession rates basically corresponds to the changes in environmental factors including precipitation increase and waterfall width narrowing. The recession rate of another waterfall decreased, but this can be explained by artificial modification of riverbed. The recession rates are very high comparing with waterfalls in other places, probably due to large amount of hard gravels transported on the weak bedrock from the upstream areas.

  • 芹沢 真澄, 宇多 高明, 宮原 志帆
    2013 年 34 巻 1 号 p. 37-53
    発行日: 2013/01/25
    公開日: 2024/12/25
    ジャーナル フリー

    The development of sand spits and cuspate forelands with rhythmic shapes was numerically predicted using the BG model proposed by Serizawa et al. under the oblique wave incidence that the angle between the direction normal to the shoreline and wave direction is ±60 degrees, given an infinitesimal perturbation as the initial condition. Then the effects of the anthropogenic factors such as the construction of a groin and an offshore breakwater to the development of sand spits and cuspate forelands were investigated using the same model. The construction of a groin induced a great impact to the sandy beach; the alteration from the field with the development of the sand spits to that with the elongation of single sand spit, as well as the acceleration of offshore sand transport because of the blockage of longshore sand transport. The construction of an offshore breakwater strengthened the wave-sheltering effect as well as the blockage of continuous longshore sand transport, resulting in dominant beach changes. The calculated results in the case with an offshore breakwater reasonably explained the example of the formation of the sand bars with two lagoons inside observed in a shallow lagoon surrounded by Black Sea and Azov Sea in Russia.

  • 村上 亘, 大丸 裕武, 向山 栄, 川浪 亜紀子
    2013 年 34 巻 1 号 p. 55-67
    発行日: 2013/01/25
    公開日: 2024/12/25
    ジャーナル フリー

    Slope deformation caused by Iwate-Miyagi Nairiku Earthquake on 14 June 2008 around Kurikoma Dam was investigated, by comparing LiDAR (Laser Imaging Direction and Ranging) data taken before and after the earthquake. An opening of the pre-existing linear depression on the ridge line and bulge of the northwest-facing slope were found to have been deformed by the earthquake. The field survey and image-matching analysis confirmed that the northwest-facing slope area from the linear depression had deformed toward the northwest side after the earthquake.

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