Geology Reference
In-Depth Information
surfaces, may persist in the landscape. The latter has a stepped appearance and can be described as
multicyclic since there is in it evidence of more than a geomorphic cycle.
In some areas, such as Cameroon, in West Africa (Mayer, 1995), stepped topography is evi-
dently associated with faulting. Three major high plains have been recognised as well as several
minor ones. The slopes separating adjacent surfaces have long been recognised and variously inter-
preted as fault scarps, or as due to lithological contrast and differential erosion. An interpretation
rather different from this and the multicyclic concept is due to Wahrhaftig (1965) with respect to
the southern Sierra Nevada, in California. Planation surfaces are a prominent feature in many
parts of the upland (Fig. 4.17).
According to Wahrhaftig (1965) the stepped topography is not only confined to granitic out-
crops but is found wherever granite is exposed in the region. He explains the forms in terms of the
behaviour of granite in wet and dry environments:
“The stepped topography is believed to be caused by differences in the rate of weathering in
the two environments to which granitic rocks in the Sierra Nevada are subject. Where buried
by overburden or gruss, the solid granitic rocks are moist most of the year, and disintegrate
comparatively rapidly … where exposed, the solid granitic rocks dry after each rain and
therefore weather slowly.”
(Wahrhaftig, 1965, p. 1166).
(a)
(b)
Figure 4.17.
Stepped topography, Sierra Nevada, California: (a) Map (Wahrhaftig, 1965); (b) sections show-
ing suggested mode of origin.
