Geography Reference
In-Depth Information
a uniform gradient except in situations of exceptional activity (e.g.
coastal cliff erosion). Thus, landslides produce a landscape with
uniform slopes. Semi-arid areas have stony, shallow soils with little
vegetation; here hillslopes tend to be concave. Temperate wet areas
are generally dominated by creep, mass movements and solutional
erosion under a dense vegetation cover and deep soils; here hill-
slopes tend to be convex. You can also examine smaller features to
see what processes have been operating, for example by checking
whether there are small mounds of sediment behind clumps of veg-
etation as an indicator of active wash processes.
The wind can be an effective agent of sediment transport if the
right type of sediment is available. Wind-blown sediment transport is
called aeolian transport . Aeolian transport dominates in arid and
semi-arid environments where there is little water. Strong winds are
needed just to carry small particles. At typical wind speeds, medium
sized sand grains (up to 0.5 millimetres) are the largest grains that can
be transported. However, the wind can carry finer dust thousands of
kilometres. The amount of material removed from the Sahara by
wind transport is estimated to be around 260 million tonnes per year.
Dune deposits are familiar landforms produced by wind. However,
erosional features in rock can also be formed because sand and dust
particles in the air can be abrasive. Abrasion by sand is usually close
to the ground (within 2 metres) as sand cannot be carried very high
due to its large size. However, finer particles can also abrade at
higher levels, smoothing rock surfaces and even whole hills, which
are often known as yardangs .
SOILS
Soil composition and formation
The weathering processes described above result in rocks becom-
ing fragmented providing small habitats for plants which then add
organic matter. This helps form soil. Soil is of crucial importance
to humans. It acts as a zone for plant growth, which provides crops,
supports animal life and holds water, influencing the amount and
quality of water in rivers and lakes.
Soil is made up of minerals, organic matter, water and air. The
amount of each of these components influences the properties of a
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