著者
早川 裕弌 松多 信尚 前門 晃 松倉 公憲
出版者
日本地形学連合
雑誌
地形 (ISSN:03891755)
巻号頁・発行日
vol.34, no.1, pp.21-36, 2013-01-25

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.
著者
宇多 高明 田中 常義 森 義将 峯 浩二 木村 尚
出版者
日本地形学連合
雑誌
地形 (ISSN:03891755)
巻号頁・発行日
vol.24, no.2, pp.215-228, 2003-04-25

Formation of the barrier where the central part of Yokohama City is located was investigated by the comparison of old maps and geological surveys. This barrier was formed as the sand spit extending northwestward from the end of Ishikawa Upland. Behind this barrier, lowland mainly composed of alluvial cohesive soil extends. In this area, jet of sand and subsidence of structural foundation were observed during the Kanto Great Earthquake. Thus, the understanding of the formation of this barrier and lowland is important to consider potential vulnerability of this area. Comparison of profiles along several sections crossing Ishikawa Upland showed that sand was supplied from this upland while forming sea cliff. Supplied sand was carried by longshore sand transport caused by wind waves in Tokyo Bay. In this area predominant wind directions are N and NE. Waves from these directions make large incident angle greater than 45 degrees reference to the shoreline direction, and this large wave incidence accelerates the formation of sand spit by the mechanism given by Ashuton et al. (2001).
著者
田村 俊和 加藤 仁美 松林 武 古田 智弘 チャタリジ デボスリ 李 穎
出版者
日本地形学連合
雑誌
地形 (ISSN:03891755)
巻号頁・発行日
vol.23, no.4, pp.675-694, 2002-10-25
参考文献数
17
被引用文献数
4

This paper presents the results of observations at different hilly watersheds in Sendai area in different periods with the aim at contributing to the study of pipe-flow initiation, pipe-outlet shift and surface-slide occurrence on valley-head slopes with increase in rainfall. The critical rainfall for the initiation of pipe-flow at channel-heads is variable with rainfall characteristics including antecedent precipitation, and with micro-topographic, pedologic and geologic conditions of the valley-head. Soil pipes at more upstream position begin to operate when total rainfall increases, for instance, in a 2 or 3 hour storm with the intensity of more than 5-10 mm/h without antecedent precipitation. This is considered the results of stepwise expansion of contributing areas and contributing soil-mass. Sediment discharge and opening of new pipes as results of intra-pipe erosion and small-scale failures occur in the case of an almost yearly storm, i.e., several tens of millimeter of total rainfall with over 10 mm/h of maximum intensity After a storm, pipe-flow continues longer on the hilislopes where deep weathering crust of andesite is distributed than on the hilislopes composed of semi-consolidated siltstone or sandstone. It is considered to be due to water-supply from saprolite to soil pipes. Surface slides are triggered with an intense rain of about 30 mm/h following to a 10 to 15 hour storm with the intensity over 10 mm/h on lower hillslope segments, particularly immediately below the convex break of slope at the lower margin of head hollows. Stronger storm, for instance, a 80 mm/h rain following to a 3 hour storm reaching to 170 mm, induces surface slides on upper hillslope segments, particularly headmost walls. Pipe outlets are observed on any slide scar. These phenomena suggest that working pipe network is switched several times with the increase of both total rainfall and rainfall intensity.
著者
羽田 麻美
出版者
日本地形学連合
雑誌
地形 (ISSN:03891755)
巻号頁・発行日
vol.28, no.1, pp.41-52, 2007-01-25

Rillenkarren are well developed on the surface of pinnacles at four karst areas, i.e., Akiyoshi Plateau, Hirao Plateau and Yamazato (Okinawa) in Japan and Lipica in Slovenia. Total 325 rillenkarren on total 67 pinnacles were selected for measurements. The width and depth of rillenkarren were measured using a carpenter's profile gauge and the slope angles of the trough of rillenkaren, i.e., slope angles of pinnacles, were measured using a clinometer. The results are as follows: 1) the slope angle of pinnacles with rillenkarren ranges between 29°and 65°in Akiyoshi and Hirao Plateaus, while it takes between 40°and 77°in Yamazato and Lipica; 2) the width of rillenkarren in four areas ranges between 1.5 cm and 6.5 cm, and it is a little narrower at Yamazato than that of the other three areas; 3) there is a difference in depth of rillenkarren, i.e., it ranges between 0.2 cm to 2.1 cm at Akiyoshi and Hirao Plateaus, between 0.4 cm to 4.2 cm at Yamazato and between 0.7 cm to 3.2 cm at Lipica; and 4) there is a common characteristic in all areas between the slope angle of pinnacles and the shape of rillenkarren, i.e., both of depth and width of rillenkarren become larger with increasing in slope angle of pinnacles.