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Wind action and arid regions
Published in F.G. Bell, Geological Hazards, 1999
Pediments are graded plains, which are formed by the lateral erosion of mainly ephemeral streams. They occur at the foot of mountain slopes and may be covered with a thin veneer of alluvium. Pediments are adjusted to dispose of water in the most efficient way and when heavy rain falls, this often means that it takes the form of sheet wash. Although true laminar flow occurs during sheet wash, as the flowing water deepens laminar flow yields to turbulent flow. The latter possesses much greater erosive power and occurs during and immediately after heavy rainfall. This, it is argued, is why these pediments carry only a thin veneer of rock debris. With a lesser amount of rainfall there is insufficient water to form sheets and it is confined to rills and gullies. Distributary channels may develop in the upper parts of pediments. Streams on pediments occasionally are active and liable to flood, to scour and fill, and tend to migrate laterally. According to King (1963), the rock waste transported across the pediment is relatively fine and is deposited in hollows, thereby smoothing the slope. The abrupt change in the slope at the top of the pediment is caused by a change in the principal processes of earth sculpture, the nature of the pediment being governed by sheet erosion, while that of the steep hillsides is controlled by the downward movement of rock debris.
Fundamental Flood Hazard Issues in the Alluvial Fan Environment
Published in Saeid Eslamian, Faezeh Eslamian, Flood Handbook, 2022
Pediments are geologic landforms characterized by sloping planar surfaces underlain by shallow or exposed bedrock (Figure 18.6). Pediments may have stable tributary drainage patterns (inactive), stable distributary drainage patterns (inactive), or small active alluvial fan floodplains inset within an otherwise stable surface. The presence of shallow bedrock on the pediment surface, although interesting from a geologic perspective, may not significantly affect surface flooding if it is buried below the level of active channel scour.
Forecasting landslides using SIGMA model: a case study from Idukki, India
Published in Geomatics, Natural Hazards and Risk, 2021
Minu Treesa Abraham, Neelima Satyam, Nakshatram Shreyas, Biswajeet Pradhan, Samuele Segoni, Khairul Nizam Abdul Maulud, Abdullah M. Alamri
The reference area for the first rain gauge, R1 represents the midland region of Idukki with nearly flat terrain, R2 and R3 represents the hilly area in the eastern side centre respectively and R4 consists of the peaks and foothills near the mountains in the northern side. The midland area of Idukki (R1) has a rugged topography, with a slope towards west. R1 is composed of pediment-pediplain complex of denudational origin. The hilly terrains can be divided into high ranges, plateau and foothills. The plateau region (R3 and parts of R2) covers maximum area and is the chief physiographic unit of Idukki. The elevation of this region varies from 500 m to 1500 m above sea level with a slope of around 30%. A major part of the district is formed by the hill ranges (R2 and R4) of Western Ghats. The slope of this region is between 30% and 50% and occasionally goes upto 80%. The peaks above 1500 m are characterized as high ranges (R4). R4 is the steepest zone with several peaks, composed of low dissected hills and valleys. The region is famous for its tea plantations and the hills have undergone several cutting and filling activities for infrastructure development, in the recent past. R2 region is formed by highly dissected hills and valleys.
Effect of spatial resolution and data splitting on landslide susceptibility mapping using different machine learning algorithms
Published in Geomatics, Natural Hazards and Risk, 2021
Minu Treesa Abraham, Neelima Satyam, Prashita Jain, Biswajeet Pradhan, Abdullah Alamri
The geology and geomorphology layers are vector files published by GSI. Both the layers are highly significant in the initiation of landslides as the physical processes of landslide triggering are related to the rock type and morphology. Geology explains the bedrock type, while geomorphology explains the interaction of rock with the environment (Youssef et al. 2015). The geology of the region is classified into six categories, viz charnockite group, khondalite group, migmatite complex, peninsular gneissic complex, acid intrusive and basic intrusive (Geological Survey of India 2010). Similarly, there are five prominent categories in geomorphology, i.e., highly dissected hills and valleys, moderately dissected hills and valleys, low dissected hills and valleys, anthropologic terrains and pediment and pediplain complex. From the landslide inventory data, it was observed that more than 70% of the landslides have occurred on terrain which is composed of the migmatite complex and peninsular gneissic complex. These regions are geomorphologically classified as highly and moderately dissected hills and valleys. The vector files were rasterized into two different resolutions, according to the DEM, for a comparative study.