HUMAN IMPACT ON LANDFORMS AND GEOMORPHIC PROCESSES

Geomorphological impact by our ancestors for most of the 5 million years or so of human development was negligible. From about 1 Ma, and particularly from the beginning of the holocene, the scope and magnitude of impacts have multiplied as a result of population growth and technological change. The earliest significant impacts by hunting, fishing and gathering societies resulted from deliberate biomass burning chiefly to encourage regrowth of new shoots and hence attract grazing animals for easier killing. This burning led to accelerated soil erosion. The development of agriculture in different subtropical centres (e.g. fertile crescent) in the early Holocene coincided broadly with a substantial increase in world population. In neolithic times, hafted polished stone axes allowed efficient forest clearance for cultivation. Development of the plough in the Old World meant that soils hitherto too heavy for agriculture could now be cultivated. valley-fill deposits with sediment dating from bronze and iron ages in Europe indicate the accelerated erosion brought about by agricultural intensification. Requirements of large amounts of wood for metal smelting doubtless contributed significantly to the loss of woodland and increased soil erosion. Cultivation requires sedentary lifestyle (sedentism), which leads to settlements and urbanisation. The emergence of urban civilisations in Egypt, Mesopotamia, India and China in mid- to late-Holocene times was conditioned by specific physical conditions—major alluvial river valleys which had low and/or unreliable rainfall. Here, successful agriculture on these fertile lands could only be achieved with major manipulation of water resources, involving modification of stream courses.

From the fifteenth century onwards, European colonialism caused the rapid transformation of large tracts of the world (e.g. North America, Australia) from often a relatively unmodified state to one highly altered through intensive agriculture by technologically advanced societies. The most notable geomorphological consequence was a rapid and marked increase in soil erosion. The mechanical technology available over the past two centuries has enabled the Earth’s land surface to be transformed on a scale and at a rate not possible under pre-industrial societies. Such changes (e.g. mining, land drainage, flood control measures and coastal engineering structures), impressive though they may be, are often localised or at most regional in their extent. Anthropogenic atmospheric greenhouse gas modifications, on the other hand, are anticipated to make future indirect human impact on geomorphology potentially global in extent, as the precipitation and temperature changes resulting from climatic change cross geomorphological thresholds in certain environmental conditions.

[See alsoagricultural impact on geomorphology, anthropogeomorphology, artificial ground, climatic change: past impact on landforms and geomorphological processes, climatic change: potential future geomorphological impacts, disturbance, permafrost degradation]