Page 117 - Soil Degradation, Conservation and Remediation

4.3 Processes of Wind Erosion 105

types of stress, including diseases, and contribute to transmission to some plant
pathogens (Armbrust 1984; Michels et al. 1995). In the long run, the cost of wind
erosion control practices can offset the cost of replanting a blown out crop. Some soil
from damaged land enters suspension and becomes part of the atmospheric dust load.
Dust obscures visibility and pollutes the air, impacts water quality, causes automobile
accidents, fouls machinery, and imperils animal and human health (Skidmore 1988).
Areas susceptible to wind erosion around the world are in the USA and Canada
in North America; in drier portions of Argentina, Bolivia, and Peru in South America;
in both European and Asiatic parts of Russia; in China, India, and Pakistan and
much of the Middle East in Asia; north and south of the equator in Africa; and
in Australia (Skidmore 1986). It is estimated that the degraded area caused by
2
6
wind erosion amounts to 5.05 × 10 km , accounting for 46.4 % of the global
degraded land (UNEP and ISRIC 1990).

4.3 Processes of Wind Erosion

There are three typical processes of soil particle movement during wind erosion.
These are saltation, suspension, and surface creep. These three processes of wind
erosion occur simultaneously. Saltation causes other particles to move in suspension
and surface creep. Neither creep nor suspension can occur without saltation. Lyles
(1988) mentioned that the following processes are involved in wind erosion: initiation,
transport (suspension, saltation, and surface creep), abrasion, sorting, and deposition
of soil particles.

4.3.1 Saltation

In saltation, fine soil particles (0.1–0.5 mm in diameter) are rolled over the soil surface
by direct wind pressure to some distance and then abruptly jump up vertically to a
height of 20–30 cm. Lifted particles gain in velocity and then descend in an almost
straight line at an angle 5–12° from the horizontal. The horizontal distance traveled
by a particle is four to five times the height of its jump. On striking the surface, the
particles may rebound into the air or knock other particles into the air before coming
to rest. Thus, saltation is a progression of particles of successive jumps (Fig. 4.2). As
the saltating particles crash into the surface, they splash up more particles that also
bounce across the surface. This bombardment of the surface causes an avalanching
effect that spreads out in a fan shape, with more and more soil particles being
mobilized downwind. Between 50 and 75 % of the soil is carried by saltation.
Bagnold (1941) suggested that saltating particles rebound from a surface at 90° and
follow a characteristic path length. It is now shown from wind tunnel experiments using
high-speed cine photography demonstrated that saltating grains impacted the surface at
an angle with the horizontal of about 10° and on average rebounded at 25°, although the