[en] Landscape Ecological Survey of the Bipindi-Akom II ... - ITTO

4. LANDFORMS
4.1 LITERATURE REVIEW
The geomorphology of Southwest Cameroon is described by Martin and Segalen (1966) and by
Franqueville (1973) at a scale of 1:1,000,000. The western part of the TCP area belongs to the
coastal lowland of late Tertiary-Quaternary age, whereas the eastern part belongs to the interior
plateau of Eocene age. At the boundary of these two zones a transitional complex is found (Segalen,
1967). At this transition different planation levels are present. The planation levels at 200 to
300 m and 600 to 800 m correspond with the erosion surfaces Africa II and I (Martin and Segalen,
1966; Franqueville, 1973). The two erosion surfaces have a well pronounced relief. They are
characterized by hills and dissected uplands with numerous small streams. The slopes of the hills
and uplands have convex upper parts and concave lower parts. Laterite banks are of minor
importance and the tropical clay soils are generally deep.
We have subdivided the area into four altitude classes which party coincide with the mentioned
erosion surfaces. The altitude classes are < 350 m, 350-500 m, 500-700 m and> 700 m.
Important processes leading to the formation of today's landforms have been tectonic movements
of parts of the Precambrian shield, e.g. block faulting along NE - SW lines, climatic changes and
erosion processes related to rapid changes of the erosion basis. These processes resulted in
different planation levels or erosion surfaces (Martin and Segalen, 1966; Buckle, 1978; Embleton
and Thornes, 1979). The physiognomy of the landscape is still being 'reformed'. The most
important process is water erosion resulting in the dissection of the area. The intensity of this
dissection is determined by the relative differences in erodibility of both soil cover and underlying
rock, and by the amount of rainfall. Differences in erodibility of the rock are caused by differences
in density of fractures and/or its mineral composition.
Table 4.1 Relief characteristics of the different landforms
Landform units Slope length Slope (%) Relief No. of Altitude Surface area
(m) intensity (m) interfluves
perkm perkm2
range (m) (km2)
Dissected erosional
plains (pd)
50-200 5-15 20- 30 3-4 40-280 110
Uplands (ul) 100-200 10-20 10- 40 3-4 120-700 480
Uplands (u2) 150-300 10-30 30- 80 2-3 120-700 690
Isolated hills (hi) 250-500 > 30 120-300 200-900 116
Complex of hills (h2)
Mountains (m)
200-350 20-40 80-200 350-700 139
- outside slopes > 400 > 30 >250 >500 100
- inside slopes 250-400 30-60 120-250
Valley bottoms (v) 0-2 30 120-300 200-900 116
Complex of hills (h2)
Mountains (m)
200-350 20-40 80-200 350-700 139
- outside slopes > 400 > 30 >250 >500 100
- inside slopes 250-400 30-60 120-250
Valley bottoms (v) 0-2