The impacts of humans on geomorphology

This chapter discusses the factors that have led to an increasing interest in the human impact in geomorphology, and then discusses the literature that appeared between c. 1960 and 2000. These developments were in four main areas: (i) intellectual and policy-related; (ii) technological developments that alter geomorphological processes; (iii) demographic trends; and (iv) proliferation of techniques for the study of landform and process change. Much work was undertaken on landforms produced by construction and excavation. Interest also developed in accelerating ground subsidence, which is a widespread phenomenon that creates engineering problems. Indeed, with increasing exploitation of tundra areas for such activities as oil exploitation, there was an increasing interest in the problems associated with permafrost. Rivers have also been greatly impacted. Humans have modified sediment transport by rivers in two ways. First, as a result of accelerated soil erosion, the delivery of sediment to rivers has increased. Secondly, burgeoning dam construction has caused sediment to be trapped in reservoirs. Far-reaching changes in channel form have been produced by land-use and land-cover changes. In addition to non-deliberate changes to river systems, there have been a whole range of deliberate modifications (e.g. channelization). Some valley bottoms areas have suffered from accelerated sedimentation while others have become incised with gullies (‘arroyos’). Studies have indicated an increasing incidence of mass movements. These have been attributed to such factors as deforestation, road cuts, changes in slope drainage and irrigation of farm land. Much work has also been undertaken on wind erosion of dryland surfaces. Human activities, most notably air pollution, have changed the nature and rate of weathering, although enhanced weathering by salt can also be accelerated by irrigation. Large numbers of people live in coastal zones, and have had a major impact on coastal landforms and processes. Many of the world's shorelines have been eroding and the complex mix of causes, natural and anthropogenic, that could be responsible have been analysed. Finally, since the 1980s there has been a growing realization of the importance of global heating for geomorphological phenomena.