in your own words describe how various human activities are destroying the natural landforms
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Man's relation with his natural environment is a complex one. While he is subject to certain natural controls and events, he also acts as the dominant force in many of the Earth's physical and biological systems. The relationship has changed with time. For thousands of years, the direction and extent of his progress were to a considerable measure dictated by his physical environment, which sometimes presented him with very difficult obstacles. Increasingly, man has become capable of altering his physical environment to suit himself. Although the object of these alterations was to improve his living conditions, in some cases they have created major long-term problems, and in still others they have been catastrophic, both for the natural environment and himself.
This book has attempted to explain the operation of natural systems and processes, but equally it has been stressed at several points that man is an important influence on many of them. In some parts of the world, the environment has been so transformed that few elements of its original nature are detectable. Even extreme habitats such as the tundra or hot deserts only sparsely populated by man have not escaped untouched, since they are often the most sensitive to the slightest interference. Many apparently natural systems are in fact control systems in which man acts as a regulator either consciously or inadvertently. At best, except for large-scale weather phenomena, natural systems are mostly modified systems. In this chapter we shall consider some of the ways in which climate, landforms, soils and ecosystems have been inadvertently altered by man.
Modification of Landforms
Mining and quarrying, deforestation, the introduction of exotic plants and animals, the use of agricultural machinery, the building and use of tracks and roads, and the overgrazing of pastures, have all, singly and in combination, profoundly altered landforms and caused accelerated erosion and deposition to occur. Where man excavates or piles up material himself, he can be regarded as a direct agent of change; where he causes natural landform processes, such as wind and water action, to accelerate or diminish, he is acting in an indirect manner. Indirect effects are by far the most widespread. Much of this influence occurs accidentally or secondarily to some other purpose; conscious attempts to influence landform processes—for example, by building coastal groynes or by reafforestation—are inevitably expensive and limited in extent.
Direct Alteration of Landforms
Man has a direct effect on the shape of landforms by excavating and piling up earth, reclaiming land from the sea and causing subsidence through mining. These activities have greatly increased since the Industrial Revolution with the development of enormous machinc power and explosives for moving material. Railway and motorway construction provides many familiar examples of man-created slopes, embankments and cuttings. Land scarification is sometimes used as a general term for disturbances created by the extraction of mineral resources; open-pit mines, quarries, sand and gravel pits arc among thoforms of scarification. Strip-mining is one of the most devastating examples of landfomr alteration of this kind. Although common in the United States, it does not occur on a widespread scale in Britain, except as a method of mining Jurassic ironstone in Northamptonshire. The effects of subsidence are common in most of the older coal-mining areas of Britain. Switchback roads, perched canals, fractured buildings and flooded depressions or flashes arc all visible manifestations of recent changes in the surface form of the ground.
Equally obvious as man-created landforms arc coal tips and other waste heaps from mining and quarrying. Many of these features are geomorpho-logically unstable, allowing various forms of mass movement to generate. When saturated by heavy rain, spoil tips arc frequently subject to sliding and flowage, supplying sediment that clogs stream channels. In 1966 at Aberfan in Wales, a major disaster occurred on a spring-saturated coal waste heap which moved as an carthflow, destroying part of the village below, including a school and many of its children. Similar problems may arise on other constructed slopes: the large number of carthtlows triggered during the building of the Panama Canal is a well-known example. More recently, the building of new trunk roads and motorways in Britain has encountered slope failure in several instances: at Port Talbot, Kecle and Sevenoaks, excavation reactivated slope shear planes which were last active under periglacial conditions during the Devensian glaciation. These sites required extensive engineering works to stabilise or avoid the slopes.
This book has attempted to explain the operation of natural systems and processes, but equally it has been stressed at several points that man is an important influence on many of them. In some parts of the world, the environment has been so transformed that few elements of its original nature are detectable. Even extreme habitats such as the tundra or hot deserts only sparsely populated by man have not escaped untouched, since they are often the most sensitive to the slightest interference. Many apparently natural systems are in fact control systems in which man acts as a regulator either consciously or inadvertently. At best, except for large-scale weather phenomena, natural systems are mostly modified systems. In this chapter we shall consider some of the ways in which climate, landforms, soils and ecosystems have been inadvertently altered by man.
Modification of Landforms
Mining and quarrying, deforestation, the introduction of exotic plants and animals, the use of agricultural machinery, the building and use of tracks and roads, and the overgrazing of pastures, have all, singly and in combination, profoundly altered landforms and caused accelerated erosion and deposition to occur. Where man excavates or piles up material himself, he can be regarded as a direct agent of change; where he causes natural landform processes, such as wind and water action, to accelerate or diminish, he is acting in an indirect manner. Indirect effects are by far the most widespread. Much of this influence occurs accidentally or secondarily to some other purpose; conscious attempts to influence landform processes—for example, by building coastal groynes or by reafforestation—are inevitably expensive and limited in extent.
Direct Alteration of Landforms
Man has a direct effect on the shape of landforms by excavating and piling up earth, reclaiming land from the sea and causing subsidence through mining. These activities have greatly increased since the Industrial Revolution with the development of enormous machinc power and explosives for moving material. Railway and motorway construction provides many familiar examples of man-created slopes, embankments and cuttings. Land scarification is sometimes used as a general term for disturbances created by the extraction of mineral resources; open-pit mines, quarries, sand and gravel pits arc among thoforms of scarification. Strip-mining is one of the most devastating examples of landfomr alteration of this kind. Although common in the United States, it does not occur on a widespread scale in Britain, except as a method of mining Jurassic ironstone in Northamptonshire. The effects of subsidence are common in most of the older coal-mining areas of Britain. Switchback roads, perched canals, fractured buildings and flooded depressions or flashes arc all visible manifestations of recent changes in the surface form of the ground.
Equally obvious as man-created landforms arc coal tips and other waste heaps from mining and quarrying. Many of these features are geomorpho-logically unstable, allowing various forms of mass movement to generate. When saturated by heavy rain, spoil tips arc frequently subject to sliding and flowage, supplying sediment that clogs stream channels. In 1966 at Aberfan in Wales, a major disaster occurred on a spring-saturated coal waste heap which moved as an carthflow, destroying part of the village below, including a school and many of its children. Similar problems may arise on other constructed slopes: the large number of carthtlows triggered during the building of the Panama Canal is a well-known example. More recently, the building of new trunk roads and motorways in Britain has encountered slope failure in several instances: at Port Talbot, Kecle and Sevenoaks, excavation reactivated slope shear planes which were last active under periglacial conditions during the Devensian glaciation. These sites required extensive engineering works to stabilise or avoid the slopes.
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