FIGURE6 Influences on soil formation
Climate
Parent material
In high-rainfall areas, soil develops rapidly, but excess moisture also washes out nutrients. In rainforests, the rich supply of decaying plant matter produces lush vegetation. However, high rainfall means that soil fertility is quickly lost. In arid regions, where evaporation is high, soils often contain too much salt to support plant growth.
Surface rocks and bedrock are broken down through weathering and erosion. The type of soil that forms depends on the parent material and the minerals it contains. A coarse, sandy soil will develop from sandstone. Bedrock that is mainly granite produces a sandy loam, while shale turns into heavy clay soil.
Acold climate with a freezing and thawing cycle will speed up the breakdown of rocks. In warmer climates, the activity of soil organisms is high, and chemical processes happen more quickly.
Soil
Time
Topography
Plants and animals
Surface features such as hills, valleys and rivers influence soil development. Soil is generally deeper on the top and at the base of a hill than on its slopes. Floodplains next to river valleys are often nutrient rich, due to sediment being deposited as floodwaters recede.
These processes take place over long periods of time. Soils undergo many changes with the passage of time.
Decaying plant and animal matter is broken down by microorganisms into material that is incorporated into the soil, making it nutrient rich.
13.3.6 How does human activity change landscapes? Human activity, such as deforestation, agriculture, urban sprawl, logging and road construction alters the natural balance and may increase erosion by up to 40 per cent in some areas. Vegetation not only provides habitats for native animals but is vital for binding the soil. Once vegetation is removed, the soil is more prone to erosion by wind and water ( FIGURE7 ). Loss of topsoil means there are fewer nutrients for plant growth, and gullies may form.
SkillBuilder discussion Geographical inquiry 1. What is a gully? 2. Why do you think this gully has formed? 3. Do you think the people
FIGURE7 Note the scale of this gully compared to the people.
in the image would be concerned about the size of this gully? Give a reason for your answer.
TOPIC13 Landforms and landscapes – diversity, significance and management 291
Made with FlippingBook interactive PDF creator