@misc{oai:niigata-u.repo.nii.ac.jp:00005235, author = {関口, 辰夫}, month = {Mar}, note = {全層雪崩が頻繁に発生する斜面では、無雪期空中写真において稜線から谷底にかけて針先で傷つけたような細い筋状の地形として判読できる。杉山ほか(1987) 、関口(1994)はこの直線状で幅の狭い溝状の地形を「筋状地形」と定義した。筋状地形は、下川(1980a)によるアバランチ・シュートよりも低標高で広範囲の日本海側の山地に分布している。しかし、その詳細な分布や地形的特徴、形成過程については未解明の課題となっている。本研究は、雪崩発生斜面に特徴的に筋状地形の地形形態や分布、形成要因について明らかにすることを目的とする。本論では、第1に全層雪崩発生斜面と筋状地形との関係、筋状地形の地形形態を明らかにする。第2に、筋状地形の分布を新潟県において詳細に調査し、分布の特徴と積雪深、標高、地形、地質との関係、および筋状地形の形成要因、筋状地形の分布を規定する要因を明らかにする。第3に、筋状地形を指標として2004年新潟県中越地震が発生した魚沼丘陵において雪崩発生危険斜面の予測図を作成し、実際の雪崩発生斜面と比較して予測図の有効性を検証する。上記の研究内容を実施するために、融雪期および無雪期空中写真により全層雪崩発生斜面の抽出と筋状地形との比較、無雪期空中写真により筋状地形分布の把握、筋状地形の地形解析を行った。また、融雪期および無雪期において現地踏査を行った。融雪期空中写真において全層雪崩が発生した斜面では約8割の斜面で筋状地形が出現し、筋状地形が存在する斜面の9割で全層雪崩が発生した。また、筋状地形のみられる斜面では6-8割で全層雪崩が反復して発生していることが認められた。筋状地形は、発生位置が稜線直下で浅い凹型か直線状の縦断形を成し、横断形は半円形~U字型の幅4-6m、深さ2-4mの溝状の地形を成している。溝の底にはたいてい基盤が露出し、雪崩によると思われる擦痕がしばしば認められた。, 筋状地形の斜面傾斜は35-55°であり、これまで報告のあった雪崩発生斜面とほぼ同様の傾斜を有していた。筋状地形を指標として無雪期空中写真を判読して全国な概略的な分布を調査した。その結果、筋状地形は北海道から山陰地方にかけての日本海側の山地に広く分布し、朝日山地から飯豊山地を経て越後山脈に至る新潟県でまとまってみられた。そこで、新潟県を対象地域として詳細な分布を調査した。その結果、筋状地形は積雪深が150-200cm以上、標高200-300mを越える地域で出現していた。筋状地形の出現する地形は、山地斜面や地すべり滑落崖、段丘崖などの特定の地形に集中してみられた。地質との関係では中・古生界の堆積岩や花園岩類から成る山岳地域で密集度が高く、新第三紀の堆積岩など軟質で新しい地質で分散した分布を示した。筋状地形の形成要因について、標高(積雪深)、地形(比高、傾斜)、地質をパラメータとし、地形・地質、密集度の異なる越後山脈(密集)、魚沼丘陵(分散)を対象として解析した結果、 35-45°を有する傾斜が主要因であると結論された。また、筋状地形の密集度の要因について数値標高データを用いて越後山脈(密集)、苗場火山(やや密集)、魚沼丘陵(分散)を対象として解析した結果、傾斜の大きい斜面の割合が魚沼丘陵で1%、苗場火山で30%、越後山脈では98%の結果が得られ、筋状地形の密集度を傾斜特性の比率として表されることがわかった。2004年新潟県中越地震で多数の崩壊が発生し、19年ぶりの豪雪に見舞われた魚沼丘陵において、筋状地形および崩壊地を指標として雪崩発生危険斜面の予測図を作成し、その有効性を検証した。翌年の2005年融雪期の空中写真から雪崩発生斜面を判読・抽出し、予測斜面と比較した結果、筋状地形の雪崩的発生率(的中率)は94.2%、崩壊地の雪崩発生率(的中率)は67.8%、全体で59.1%となり、筋状地形を指標とした雪崩発生危険斜面予測図の有効性が検証された。, Mountain slopes, where the full-depth snow avalanches (FDSAs) happen, are frequently characterized with a narrow straight landform. It can be recognized as a needle scratch on aerial photographs taken in snow-free periods. SUGIYAMA et al. (1987) and SEKIGUCHI (1994) defined the landform as "avalanche furrows". Comparing to the avalanche chute (Shimokawa, 1980a), the avalanche furrows distribute in lower altitude and located widely in the mountain areas along the Japan Sea coast. However, neither detailed distributions, geomorphological features nor formation process have been clarified so far. In this study, the geomorphological features and distribution characteristics of avalanche furrows are investigated, and the formation factors are discussed. Firstly, the relation between the FDSAs slope and avalanche furrows, and the geomorphological features of avalanche furrows are examined. Secondly, the distribution of avalanche furrows in Niigata Prefecture are investigated : distribution characteristics, relation with snow-depth, altitude, landform and geology. Then, formation factors of the avalanche furrows are revealed. Thirdly, the avalanche hazard map in the district of Uonuma hill was compiled. This area was heavily devastated by the Niigata-Ken Chuetsu Earthquake in 2004 and precise geographical features were obtained immediately after the disaster. Predictions agreed fairly well with the avalanche events, and the effectiveness of the hazard map has been testified. Above results were obtained with the following procedures. FDSA release was extracted by aerial photographs taken in snow-melting periods, while the avalanche furrows by the ones in snow-free periods. Then, geomorphological features were analyzed. Field observations were also carried out both in snow-melting and snow-free periods. Avalanche furrows are found to form on 80% of the FDSAs slopes, while FDSAs took place on 90% of the slopes with avalanche furrows. On the other hand, FDSAs occurred repeatedly on 60-80% of the slopes with the avalanche furrows. Avalanche furrows start near the ridge and extended to the valley bottom with the shallow concave or vertical straight patterns. They have a semicircular or U-shaped cross profile af 4-6 m wide and 2-4 m deep. The upper and middle part of the avalanche furrow show very smooth surfaces with many striae produced by FDSAs; mostly bedrock was exposed in the lower part. The slope inclinations of avalanche furrows were from 35° to 55°, which are equivalent to the FDSAs slope angle. The avalanche furrow distributions were investigated all over Japan by the aerial photographs taken in snow-free periods. The avalanche furrows were found to exist widely in the mountain areas of Hokkaido to the San-in Regions along the Japan Sea coast., Particularly, the district from Asahi mountain range in Niigata Prefecture to Echigo mountain range through Iide mountain are highly concentrated. Thus, Niigata Prefecture was set as a study area and detailed analysis were conducted. As a result, the avalanche furrows are found to appear in the region where snow cover amounts larger than 150-200cm deep and the altitude higher than 200-300m. Landforms, where avalanche furrow were highly concentrated, correspond to the mountain sides, landslide scarps, river terrace scarps, caldera walls and glacial cirques. From the geological point of view, they appeared remarkably in the area of volcanic rocks (tuff, quartz trachyte, andesite, etc.), granite, metamorphic rock and tertiary. Formation factor of avalanche furrows were analyzed as functions of the altitude, which roughly corresponds to the snow-depth, geomorphological features, such as the elevation and the inclination, and geology. Regions of Echigo mountain and the Uonuma hill were chosen as the study area; density of the avalanche furrows are high in the former and low in the latter. Comparison in detail revealed that the slope inclinations of 35-45° were the key factor for the formation of avalanche furrow. In the analysys, the digital elevation model (DEM) data in the regions of Echigo mountain, Naeba volcano, and the Uonuma hill were also utilized; each corresponds the area of dense, middle and sparse respectively. Ratio of the slope inclination over 250 were obtained as 98% in the Echigo mountain, 30% in the Naeba volcano and 1% in the Uonuma hill. That is, we can conclude that the slope inclination is a main factor to determine the avalanche furrows concentration. In order to minimize the snow avalanche disaster, a hazard map was compiled with utilizing the distributions of avalanche furrows as well as the landslides. In the research area of Uonuma hill, a number of landslides happened due to the Niigata-Ken Chuetsu Earthquake in 2004 and successively we suffered very heavy snowfall after an interval of 19 years. The release of FDSAs were extracted by aerial photographs in snow-melting period of 2005, and they were compared with the hazard map. FDSAs were recognized on 94.2% of slopes with the avalanche furrows and 67.8% of slopes with the landslides; 59.1% in total were accurately predicted., 新潟大学, 平成20年3月24日, 新大博(学)第59号, 新大博(学)乙第59号}, title = {空中写真を活用した筋状地形の研究 : 全層雪崩と関連して}, year = {2008} }