Recent sedimentologic and geologic studies have revealed that coastal alluvial-fan sedimentation is sensitively influenced by sea-level changes. A brief introduction to recent understanding of the sea-level control is made in this paper from geomorphologic point of view. The framework presented elsewhere by the author gives a synthetical explanation of morphologic evolution and depositional processes of coastal alluvial-fans controlled by relative sea-level changes and resulting stratigraphic sequences. This framework should be further examined through field observations and thereby will be improved.

抄録全体を表示

Appricability of the quantification method II to the discrimination of landslide-prone areas was examined. Six quantities obtainable from a topographical map and likely to be related to landslides, were treated as representative of the geomorphological information. The six quantities are elevation, slope inclination, depth from the summit level, height above the river level, relative relief, and drainage density. Data were collected from each grid square laid on the topographical maps Shinano-Nakajo and Takafu, in which a large number of landslides have occurred. Accuracy of the discrimination was examined by the following four factors. They are precision of elevation measurement on the map, size of the grid square, categorization of the geomorphological items, and data sampling from the grid considered to be safe from landslide risk. The accuracy was largely affected by the data sampling. A simple improvement of the data sampling raised the accuracy of discrimination from 74% to 95%, as judged from a comparison with the actual landslide data.

抄録全体を表示

　海面上昇が予測されている中，平均標高が数mと平坦な環礁州島では海岸沿岸域で強い影響を受ける．環礁における適応策として，堤防の設置，養浜といったハードウェア対策に加えて，島の形成に寄与する有孔虫の保護が挙げられる．このような中，人口集中などに伴う水質悪化やリーフの環境が変化しており，有孔虫の減少が危惧されている．このため，有孔虫の生息域を調べ，保護区域の設定等の対策が重要となる．本研究では，予備調査により明らかになった「有孔虫の藻類への付着，有孔虫生息域の地形的特徴」を予備知識として，新たな空撮を行い，生成した地理空間情報を組み合わせた画像解析による有孔虫生息域の推定を行った．有孔虫生息可能性比率との対応や分類精度を参照し，n次元画像を用いたマジュロ環礁の離島における有孔虫生息域を示した．

抄録全体を表示

東北地方の新庄地域から, 地すべり地形の発達が顕著で, しかも, ある種の特色をもつ地区をカ4ヵ所選び, それらの空中写真と判読例を示して, 単位地すべり地形の認定の仕方と分布図上での表現法およびある種の特色を示す単位地すべり地形の適切な表現法について述べた。

抄録全体を表示

Sediment movement on the KUROBE alluvial fan is estimated. The results lead to the broad understanding of the relation between the transition of topography in a long term and the river characteristics at the present time. The analysis of topographic features is shown to be usefull for the long term river planning.

抄録全体を表示

　高レベル放射性廃棄物の地層処分の安全評価に資するため, 日本原子力研究開発機構では, 広域を対象とした長期的な地下水流動評価手法の整備を進めている. 本研究はその一環として, 将来的な寒冷気候の到来に伴った地下水流動状況を予測評価するために, 凍土が形成されていた可能性の高い北海道幌延地域を対象として, 空中写真と高精度 DEM (数値標高モデル) を使用した地形解析を行い, 最終氷期から後氷期への地下水流動の変化要因について検討した. その結果, 幌延地域では氷期に周氷河性の平滑斜面が広く発達し, 後氷期に入ると降水量の増大に伴ってこの平滑斜面が侵食され, 相対的に急傾斜の後氷期斜面が形成されたこと, およびこの後氷期の侵食作用は対象地域内で一様ではなく, 地質の違いによって明瞭な差があることがわかった. すなわち, 勇知層や更別層では平滑斜面の60％以上がすでに侵食され, 一部では谷の切り合いにより稜線高度が低下していた. 一方, 声問層や稚内層では水系密度が低く, 平滑斜面の40％未満を侵食するに留まっていた. また, 後氷期に形成された谷は, 声問層以上の比較的浅い谷と稚内層以下の比較的深い谷とに分類できることがわかった. これらに加え, 対象地域の北部と南部での河床高度の変化の違い等について検討した結果, 最終氷期から後氷期への地下水流動の変化要因として①永久凍土の消滅, ②本流河床標高の上昇, ③降水量の増加が重要であると考えられる.

抄録全体を表示

On the Shirasu slope, most parts of slope failures caused by rainstorms have often occurred near knick lines. On the slope with some knick lines, tha failures sometimes occur at several elevations.
On the Shirasu plateau, there exist the paleovalley which characterized by no waters. Paleovalley has some knick points and these knick points continue downstream to the knick lines on the Shirasu slope. Paying attention to the topographical features such as a knick point, we examined the possibility of forecasting the slope failure sites.
We regarded a headward of valley as the circle which inscribed around the ridge lines on the topographical map, and we get the average inclination within the circle and the radius. Measured by this method on varied scales of valley, collapsed and not collapsed slopes could be discriminated by the approximate formula “i=2.39r^-0.50” (i; average inclination, r; radius). Under the same method above we also defined the efficient hight “He=h²/2r” (h; relative height, r; radius) as a meaningful values of topography, and calculated “He” of every slope. Using these formulas of the research on the case of Kagoshima disaster in 1993, we clarified that most collapsed slopes have efficient height above 11.4 (m).

抄録全体を表示

In the coastal area of Fukushima Prefecture, there develops a series of landforms consisting of hills 100-50m in height, terraces 50-30m, and alluvial plains. The valleys dissect the hills and terraces, both of which consist of Pliocene sandstone or siltstone. There are two types of valley forms in transverse profiles, concave valley (Muldental) and V-shaped valley (Kerbtal, partly Sohlen-kerbtal). These two types are systematically distributed due to the topographical location, and Muldental is accompanied with an undulating landform of small relief, and Kerbtal with linear or convex slope of relatively large relief.
As the undulating landform is introduced from an almost flat plane by means of surface denudation, sufficient running water and potential relief are not always necessary for its formation. On the other hand, Kerbtal can not be formed without sufficient water and potential relief enough to undercut the channel bed. Consequently, the undulating landform is in the core area of hills and terraces, free from the Kerbtal development which is seen in areas with linear slopes surrounding the core area.
Where the undulating and the linear slopes exist side by side, there appear breaks of hillslopes, knickpoints, in the longitudinal profiles of streams, and so on, forming a front line of topographic unconformity.
The undulating landform area and the linear landform area can be distinguished each other, and patterns of the spatial combination of both areas appear in various features of hill morphology.

抄録全体を表示

The Ojika Peninsula is situated in the southernmost part of the Sanriku Rias Coast and it embraces the Sendai Bay. In this peninsula, four terraces are distributed; 90-75 in, 60-40 m, 20 m, and 10-8 m high above sea-level respectively. They are underlain with thin layers of gravels composed of spheritic and rounded gravels, but at some places the terraces are defficient of such gravels. The most part of the terraces are dissected into hilly land. At a higher level, flat-topped surfaces are recognized in the whole area; these are correlated with the erosion surfaces distributed in the Kitakami Mountains.
Before the coastal terraces were formed, this peninsula had been exposed to subaerial processes for such a long time that the erosion surfaces were formed, many subsequent valleys are cut, producing the initial form of the present Rias coast. Due to the successive uplifts of the land after such a sequence, the above-mentioned four terraces were formed.
Wave action eroded the most part of the lowest terrace and the mouths of the waste-filled valley.

抄録全体を表示

岩木山北麓に広く分布する火山麓扇状地の構造と形成時期を明らかにするため, テフロクロノロジーの手法で同時面を把握し, その地形面を作る堆積物の供給時期を, 6層準の指標テフラを用いて7期に分実類した。指標としたテフラは八戸軽石 (約1.3万年前), 大不動軽石 (約2.6万年前), 上部赤紫ローム層, 洞爺火山灰 (約10万年前), 下部赤紫ローム層, 新法師軽石層 (リス氷期頃) である。
岩木山北麓の火山麓扇状地は, 堆積物の供給時期と地形面形成期とが明瞭に識別できるような様式で発達している。それぞれの時期の扇状地面は, 堆積物が似通った層相を持ち, それぞれの堆積面は同じ頃に形成されており, 北麓一帯に広く追跡できる。
それぞれの堆積物の供給は, 谷の発達による崩壊現象が起源ではなく, 谷形成以前の山体崩壊や火山活動に伴う岩屑の供給と関係が深い。すなわち岩木山北麓の火山麓扇状地は小規模土石流が長い時間をかけて少しずつ累積して形成されたのではなく, 大規模な岩屑なだれや火山活動に伴う土石流 (ラハール) によって形成されたものと考えられる。

抄録全体を表示

The Nonodake Hill is an isolated hill surrounded by the alluvial Sendai Plain. It is consisted of two-storied erosional surfaces, the Nonodake (180-220m) and the Ishibotoke (100-140m) surfaces, which cut the bedrock of alternating Miocene breccia and conglomerate, Pliocene tuffaceous sandstone and shale formations. On the Ishibotoke surface, wide open and concavesloped valleys belonging to a former cycle of erosion are preserved. In these valleys the Ishibotoke surface appears as a rolling surface with low interfluves and gently concave profiles of slopes. Along the northern foot of the hill, a dissected terrace, the Osato surface (30-40 m), is distributed.
The following conclusions are obtained from the geomorphological analysis of the hill :
1) After the erosional surfaces with the concave-sloped valleys had been formed, there arose a tilting upheaval which lifted the northern part of the area more than the southern.
2) As a consequence the erosion was rejuvenated and the uplifted block suffered the dissection in the form of retreating knickpoints in the dissecting valleys, then the concave-sloped valleys and the rolling surface diminished to be preserved partly near valley heads and divides. Some tributaries of the concave-sloped valleys were captured by the younger streams.
3) Through the last tilting movement emerged the Osato terrace surface, which was also dissected later.
4) Recent transgression which was common to whole Japan spread into this area and the dissecting V-shaped valleys were transformed into Solthin-kerbtal as are seen today.
5) The asymmetrical drainage pattern and topographic profile in the hill are attributed endogenetically to the tilting movements, and exogenetically to the existence of steep scarp at the northern fringe by the lateral erosion of the Hazama river, and proceeded rejuvenation in the southern area of the hill.

抄録全体を表示