Geoscience Reference
In-Depth Information
uneven, ranging from 450 mm in the southern and western lowlands to 1,600 mm in
the northern lowlands and eastern highlands. The occurrence of summer rains is an
important factor in subsistence crop production in Lesotho. The tropical and climatic
variations impose severe constraints on agriculture; only 13 % of the land is suitable
for arable cropping and in recent years, this has dropped to about 9 % because of
extensive land degradation, gully erosion, residential and industrial encroachment.
Furthermore, the country exhibits marked seasonality, with even the lowlands
experiencing winter frosts. Temperature in the lowlands fluctuates around 30 to
5
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C. Topography has played an important role in the formation of the soils
of Lesotho because of variations in slope and altitude. On steep slopes in the
mountains, soils development is impaired because of the greater influence of erosion
and low temperature, which led to the formation of immature skeletal soils. In
the foothills, where volcanic materials meet the sedimentary formations, colluvial
activities have caused a great deal of variation in the geological materials. In the
lowlands, most of the soils contain dissolved material and suspended fine clay
through the lateral flow of water from soils on the surrounding slopes to depressions
and bottom lands subsequently forming hydromorphic soils.
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Desertification in Lesotho
Soil erosion has been a problem in Lesotho since the early 1900s. A lot of
rehabilitation work has been done in the past but the rate of soil erosion is still high
and land degradation caused by drought, torrential rains and overgrazing which lead
to inadequate vegetative cover. The rate of soil erosion in Lesotho is 41 tons of soil
per hectare per year.
The southern part of Lesotho is faced with the problem of desertification due
to low annual rainfall, which ranges from 200 to 450 mm. Overstocking more
especially of small livestock resulting in overgrazing and rampant trampling that
destroys the soil structure. Plowing along steep slopes exacerbates the rate of soil
erosion and result in formation of gullies Fig.
8.3
. These factors make the soil
susceptible to water and wind erosion.
Wind erosion is not well documented but poses a major problem during the
months of August and September, when dust storms occur frequently. At times they
are capable of blocking the sunlight. However, there are no formations of sand dunes
unlike many other areas of the world. Early spring rains quickly wash away the small
piles of soil deposited by wind.
Water erosion is a major problem caused by the heavy rainfall which occurs in
spring and summer. Due to the topography, highly erosive soils and overgrazing, a
lot of topsoil is washed away resulting in formation of gullies, and this drops the
water table of the adjacent areas. As a result there is degradation of rangelands and
desertification.
Rangelands present the biggest challenge to Lesotho and a serious loss to
biodiversity. Lesotho is experiencing a high loss of soil largely as a result of poor
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