13 0 0 0 OA 東北地方太平洋沖地震とそれ以降の降雨による斜面崩壊 : 茨城県北部の花崗岩山地における事例
- 著者
- 木下 祐介 八反地 剛 八木 勇治 江崎 隼輝 奥村 大輔
- 出版者
- 日本地形学連合
- 雑誌
- 地形 (ISSN:03891755)
- 巻号頁・発行日
- vol.35, no.1, pp.25-39, 2014-01-25
The 2011 East Japan Earthquake caused landslides across the Northern Kanto and Tohoku Regions. The purpose of the present study is to reveal the characteristics of shallow landslides induced by the earthquake and subsequent rainfall in granitic mountains located in northern Ibaraki Prefecture, Japan. Total 140 shallow landslides were identified through interpretation of aerial photographs and fieldwork. Among the 140 landslides, 65 were directly triggered by the main shock (March 11 to 18, 2011), and the rest 75 were triggered by rainfall events or other earthquakes from March 19 to December 15, 2011. The most of them are shallow landslides with a slip plane of granitic soil (grus). Bedrock or weathered bedrock is exposed on some landslide scars in the area underlain by biotite granite where soil is thinner. Among the 87 landslides, which occurred on natural hillslopes, 50 landslides slid eastward (NE to SE). The bias in landslide direction on natural hillslopes would correspond to the direction of crustal movement of the main shock.
5 0 0 0 OA 泥炭湿地におけるケルミ・シュレンケ複合体の形成過程 : カレックスモデルを用いた検証
- 著者
- 岡田 操
- 出版者
- 日本地形学連合
- 雑誌
- 地形 (ISSN:03891755)
- 巻号頁・発行日
- vol.31, no.1, pp.17-32, 2010-01-25
- 参考文献数
- 19
- 被引用文献数
- 1
String-flark (kermi-schlenke) complex pattern is a characteristic micro-topography in boreal mires. It consists of linear ridges aligned perpendicular to the slope, separated by water zones that are more sparsely vegetated. Various explanations for the formation process of this micro-topography have been proposed, however, the process by which oriented string-flark complex pattern originates is not clear. Nevertheless, as pattern formation occurs very slowly in nature, computer simulation offers useful help in understanding the formation process. In the present study, the formation processes have been defined by classifying the development stages of the string-flark complex pattern. While evaluating the existing theories on origin, a computer program has been coded to simulate using Carex Model, and verified the formation process. Carex Model is based on the growth processes of bog vegetation. Hence it can simulate changes in peat layers and thus predicts the formation of the diverse micro-topographies of mires. The result implies that string-flark complex pattern is generated by the accumulation of additional litter brought by snow-melting flow. Water level changes under the influence of prevailing hydraulic conditions and the patterns are formed with the selective growth of vegetation.
3 0 0 0 OA 玉川上水における法面の非対称とその成因
The Tamagawa Josui Canal was excavated in the early Edo period to conduct city water from the Tama River to Edo. In this canal there is a conspicuous asymmetry in slope morphology between both banks. That is, the left bank has steep cliff while the right bank has gradual slope with short cliff on upper part of the bank. To elucidate the cause and the forming process of the asymmetrical slope morphology, we investigated geomorphic surface process on each bank. During January 11th to December 24th in 2003, we set up traps on each bank and weighed monthly the volume of debris fallen down from upper part of the slopes. According to longitudinal measurement of debris volume, failure of soil surface occurs throughout the year on the slope of the both banks, though total amount of debris production on the left bank were twice as high as that on the right bank. Amount of debris in winter season was 9.7 times higher than in summer season. Especially from January to March, debris was intensively produced on the right bank. Debris production was evident to be induced by needle ice. Geomorphic surface processes on the north-facing right bank are as follows. In winter season, frost columns are formed on the surface of Kanto Loam (volcanic ash sediment) under low soil temperature and high soil moisture. A few days later, when needle ice melt, small grains are left on the surface of Kanto Loam. Grains are eventually carried down by the rainfall or winds to lower part of the slope. As a result, cliffs on upper part of the bank retreat and gentle slopes of the lower part expand. On the south-facing left bank, debris production is little throughout the year. On this bank, cliffs are so dried up in winter because of rich sunshine that needle ice don't arise even air temperature fell down under the freezing point. Instead, many cracks arise lengthways and blocks of soil fall down in occasion of heavy rain. In this way, the cliff retreats with its vertical shape. The Tamagawa Josui Canal is supposed to have maintained its original form when it had been brimmed with water, from the construction time till 1965 when water flow stopped by the disuse because of completion of filtration plant. After water flow was stopped and canal became to be dried up, asymmetry of the trench profile has been formed.
- 著者
- 豊田 新 成瀬 敏郎
- 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.5, pp.811-820, 2002-12-25
- 参考文献数
- 23
- 被引用文献数
- 15
風成塵の主要鉱物である微細石英の電子スピン共鳴(ESR)分析によって最終氷期最盛期MIS 2と完新世MIS 1における日本列島および東アジア各地の堆積物を分析し,東アジアのジェット気流と北西季節風の挙動を復元した.MIS 2には韓国や瀬戸内海以北は酸素空格子信号強度が高く,シベリア高気圧から吹き出した北西季節風によって北部アジア大陸に広がった砂漠から風成塵が多量に運ばれた.瀬戸内海〜関東を結ぶ線から沖縄本島までは中国内陸砂漠から夏季亜熱帯ジェット気流によって風成塵が運ばれ,宮古島以南は中国南部あるいはチベット高原から冬季亜熱帯ジェット気流によって風成塵が運ばれた.台湾は第三紀が広く分布する台湾山脈から海岸にもたらされた酸素空格子信号強度の低い細粒物質が混入するために風成塵堆積物の信号強度が低い.当時はポーラーフロントの北限が瀬戸内海から関東を結ぶ地域にあった.MIS 1にはポーラーフロントが北海道まで北上したために,風成塵(黄砂)は中国内陸砂漠から韓国をはじめ,北海道にまで運ばれるようになった.
3 0 0 0 OA 2001年6月29日豪雨によって阿蘇火山で発生した斜面崩壊とラハールの特徴
- 著者
- 宮縁 育夫 大丸 裕武 小松 陽一
- 出版者
- 日本地形学連合
- 雑誌
- 地形 (ISSN:03891755)
- 巻号頁・発行日
- vol.25, no.1, pp.23-43, 2004-01-25
- 被引用文献数
- 3
The 29 June 2001 rainstorm (total 238 mm; maximum hourly rainfall 98 mm) triggered more than 700 landslides and associated lahars at Aso Volcano, central Kyushu, SW Japan. Most of the landslides were concentrated in a 20-km^2 area that includes the northeastern slope of post-caldera central cones, the northern slope of Nekodake Volcano and the eastern caldera wall. We mapped landslides triggered by the storm using field observations and 1 : 20,000-scale aerial photography provided by the Kumamoto District Forest Office taken in December 2001. Most of the triggered landslides were shallow (about 1 m thick) soil slips in unconsolidated airfall tephra layers overlying lava flows and pyroclastic rocks. Average volume of the landslides was 550 m^3, but some had volumes exceeding 10,000 m^3. The rupture surfaces of most landslides were formed near the boundary between upper blackish and lower brownish tephra layers. These layers have differences in permeability, grain size and soil hardness. Most landslides mobilized completely into lahars, traveling a few kilometers along stream channels. Although some lahars eroded channel side slopes and transported boulders (2-3 m in diameter), most contained up to about 80 percent silt-to-clay-size particles, similar in composition to the original landslide debris. Sediment discharge volumes by the tephra-slip-induced lahars were estimated at an order of 10^3-10^4 m^3/km^2 using sediment volumes trapped by check dams. These volumes are similar or one-order of magnitude smaller than the volumes of the 1953 and 1990 landslide disasters in the same region. The characteristics of landslides and lahars and their estimated volumes provide important information about landslide and lahar hazards at Aso Volcano.
2 0 0 0 OA アンコール・ワットを構成する砂岩およびラテライトの風化環境と風化プロセス
Weathering environment at two study sites of Angkor Wat were analysed together with mineralogical and physico-chemical behaviour of building stones of sandstone and laterite. In order to store the set of data of air temperature and relative humidity at intervals of 30 minutes, two data loggers were installed at Elephant gate (Site 1) and West causeway (Site 2), between 5 September 2000 and 10 September 2001. The results show that Site 1 had more severe temperature and humidity changes (-5℃/30min, 24%/30min in maximum) than Site 2 (-4℃/30min, 19%/30min). In addition, Site 1 had a high frequency of wetting and drying cycles (73 cycles) compared to Site 2 (6 cycles). These measurements argue that wet-dry alternation and salt efflorescence are major in exfoliation on sandstone surfaces at Elephant gate. The laterite composed of goethite, hematite, quartz and kaolinite has no swelling clay minerals. However, the laterite has small tensile strength (1.2 MPa) than the sandstone (3.5 MPa), as well as low durability for wet-dry repetition. It is recognized that slaking of the laterite due to fluctuation in water level at the moat has caused subsidence of West causeway.
- 著者
- 津村 宏臣
- 出版者
- 日本地形学連合
- 雑誌
- 地形 (ISSN:03891755)
- 巻号頁・発行日
- vol.25, no.3, 2004-07-25
2 0 0 0 OA エコーチップ硬さ試験機の紹介とその反発値と一軸圧縮強度との関係に関する一考察
- 著者
- 青木 久 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.25, no.3, pp.267-276, 2004-07-25
- 被引用文献数
- 8
We introduce the equotip hardness tester and present the relations between the Equotip rebound value (L-value) and the unconfined compressive strength (UCS) for intact rock samples. Based on existing data and the results of our laboratory tests, an equation is derived connecting UCS (MPa) and L-value obtained from single impacts, L_s, and porosity, n (%), using multiple linear regression analysis: it is found that UCS = 0.079 e^<-0.039n> L_s^<1.15>
2 0 0 0 OA カレックスモデル : 植生生長関数を介した高層湿原の微地形形成モデルの提案
- 著者
- 岡田 操
- 出版者
- 日本地形学連合
- 雑誌
- 地形 (ISSN:03891755)
- 巻号頁・発行日
- vol.29, no.3, pp.281-300, 2008-07-25
- 被引用文献数
- 2
In bog mires, peat formation depends largely on plant growth, the amount of which in turn is influenced by rates of primary production, soil pH, sunlight, and ground, air and water temperatures. Plant growth is also affected by soil saturation and thus groundwater, which in turn are influenced by meteorological factors such as precipitation and evapotranspiration as well as hydrological factors such as inflow, outflow and storage. The flow of groundwater is influenced by peat composition, where a lack of water results in plant death, followed by partial decomposition of plant matter. This accumulates contributing to the upper layers of peat. As time progresses, the plant matter undergoes varying degrees of decomposition and consolidation producing peat of variable density, porosity, and permeability. The model proposed in this paper focuses on groundwater table, the most significant factor in peat formation. The characteristic of this model is the determination of the relationship between plant growth and groundwater table under variable conditions. In a given topographical configuration, if boundary conditions such as the inflow and outflow of rainfall and surface soil are manipulated, unsteady flow calculations reveal changes in water level. If this is iterated for an entire season, vegetation grow and peat will accumulate depending on the mean seasonal water level. This relationship is predicted using the growth function of vegetation, which is determined from growth simulations incorporating actual data from the primary production of specific plants. Iterated over the course of several years the thickness of peat layers gradually changes, giving rise to a conspicuous topography. This model demonstrates that causes of topographical formation, which to date could only be determined qualitatively can now be done quantitatively. Based on the growth processes of bog vegetation, this paper proposes a "Carex Model", which simulates changes in peat layers and thus predicts the formation of the diverse micro-topographies of bog mires.
1 0 0 0 OA グレイシオハイドロアイソスタシー(用語解説)
During the growth of an ice sheet the continental crust beneath and near the ice sheet subsides, while in the decay period of glacier ice the crust is unloaded and rebounds. The process is called glacio-isostasy. The volume of sea water decreases during ice growth, while it increases during ice decay. The changing water load causes the vertical movement of the oceanic crust. The process is referred to as hydro-isostasy. These two processes combined are involved in glacio-hydro isostasy, i.e., the Earth's response to changes in ice and water loading during glacial cycle. The outline of a model for glacio-hydro isostasy is described and an application of the model to the northwestern Kyushu area is briefly introduced.
1 0 0 0 OA シュミットハンマー : 地形学における使用例と使用法にまつわる諸問題
We briefly review some problems arising in papers on the Schmidt hammer used in a geomorphological context. There are several types of Schmidt hammer, and many measurement methods including ways of collecting data have beeen proposed, but no standard method for taking measurerements has yet been established. We propose continueous (repeated) impacts for assessing the hardness of intact rock and single impact for assessing the hardness of a rock surface, including the weathering layer.
1 0 0 0 巨大崩壊, 岩屑流と河床変動
1 0 0 0 OA 透水性の異なる砂岩と泥岩からなる丘陵地における斜面崩壊の発生機構と発生位置
To study the effect of bedrock permeability on hill morphology, we performed hydrological measurements and a slope stability analysis in the hilly terrains underlain by unconsolidated sandstones and consolidated mudstones around Mt. Kanozan, Boso Peninsula, central Japan. The sandstones provide high round-top hills with the low drainage density, and the mudstones comprise low rugged hills with the high drainage density. The permeabilities of sandstone and mudstone were 2 × 10^<-3> cm/s and 5 × 10^<-6> cm/s respectively. Slope failures in both areas have distinctive features: (1) failure-generating areas in the sandstone hills are confined to the lower parts of steep slopes adjacent to valleys; and (2) the slope failures in the mudstone hills take place almost on convergent hollows locating at the upper part of the hill slopes. The rainfall-runoff characteristics differed in the two areas. No increase in discharge was observed in the sandstone areas even during rainstorms. This implies that vertical percolation and deep groundwater flows are dominant in the sandstone hills. In contrast, rapid runoff and a large peak discharge responsive to rainfall were found in the mudstone areas. This indicates that subsurface storm flows mainly contribute to the discharge in the mudstone hills. A stability analysis on slipped slopes in both sandstone and mudstone areas revealed a difference in their instability mechanisms. Slope failures in the sandstone hills were caused by reduction of soil cohesion as a result of increasing moisture content in the regolith. Slope failures in the mudstone hills result from increasing pore water pressure derived from a rising subsurface water level in the regolith zone. These differences appear to be a result of the different behaviour of percolated water according to the different permeabilities of the two bedrocks. Morphology in the hilly terrains around Mt. Kanozan, such as the relative heights of the ridges, must be controlled by these slope instability mechanisms and locations of the slope failures.
1 0 0 0 IR 乾燥粒子流の流動特性(2003年度春季研究発表会)
1 0 0 0 IR 1. 三重県尾鷲市の豪雨(2002年度春季研究発表会)
- 著者
- 島津 弘
- 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, 2013-01-25