574
Climatic Geomorphology
the "two-stage" one proposed by Linton for boulder inselbergs and tors. This theory has
been checked in quartz diorite pit fronts in southern Cameroon, where a 50-m dome is
surrounded by weathered material (Boy6 and Frisch, 1973). Some roadcuts also permit the
observation of these incipient domical forms (Thomas, 1978). Domes are located on the
less fractured parts of the weathering front. Stripping is progressively carried out by fluvial
action and domical forms slowly appear on the land surface as small cupolas,
which announce an embryonic or incipient domed inselberg (Thomas, 1978; Twidale,
1982) (Figure 21.41).
In general, small bornhardts are related to a single episode of deep regolith excavation
that can reach 100 m. When trying to explain great dome inselbergs, however, difficulties
arise (Thomas, 1965; 1974). Nevertheless, if a continuous weathering at the slope foot is
admitted, then stripping produces a surface lowering of the surrounding plains and
bornhardts several hundred metres high can be satisfactory explained (Figure 21.42).
Consequently, it is a matter of repeated alternations between weathering and denudation
phases throughout a long period of geological time (Willis, 1936; Btidel, 1957; Twidale,
1964, 1982; Thomas, 1978, 1994). Thus, many great domed inselbergs are geologically
very old.
The scarp retreat theory does not explain some forms related to the contact rock-plain
and rock-saprolite. Instead, the exhumation hypothesis justifies the existence of embryonic
domes and microforms generated at the weathering front (polygonal weathering, tafoni,
gnammas, pseudokarren, caves, and so forth) (Twidale, 1982a; Thomas, 1994; Vidal
Romanf and Twidale, 1998). It also explains the genesis of stepped slopes (Twidale and
Bourne, 1975, 1978) and mushroom profiles (Twidale, 1962), which together with tafoni
lines at different heights in Ayers Rock (Uluru) (Twidale, 1978), indicate an older
Figure 21.41. Embryonic dome forms on a savanna region. Masai Mara, Kenya.
Climatic Geomorphology
the "two-stage" one proposed by Linton for boulder inselbergs and tors. This theory has
been checked in quartz diorite pit fronts in southern Cameroon, where a 50-m dome is
surrounded by weathered material (Boy6 and Frisch, 1973). Some roadcuts also permit the
observation of these incipient domical forms (Thomas, 1978). Domes are located on the
less fractured parts of the weathering front. Stripping is progressively carried out by fluvial
action and domical forms slowly appear on the land surface as small cupolas,
which announce an embryonic or incipient domed inselberg (Thomas, 1978; Twidale,
1982) (Figure 21.41).
In general, small bornhardts are related to a single episode of deep regolith excavation
that can reach 100 m. When trying to explain great dome inselbergs, however, difficulties
arise (Thomas, 1965; 1974). Nevertheless, if a continuous weathering at the slope foot is
admitted, then stripping produces a surface lowering of the surrounding plains and
bornhardts several hundred metres high can be satisfactory explained (Figure 21.42).
Consequently, it is a matter of repeated alternations between weathering and denudation
phases throughout a long period of geological time (Willis, 1936; Btidel, 1957; Twidale,
1964, 1982; Thomas, 1978, 1994). Thus, many great domed inselbergs are geologically
very old.
The scarp retreat theory does not explain some forms related to the contact rock-plain
and rock-saprolite. Instead, the exhumation hypothesis justifies the existence of embryonic
domes and microforms generated at the weathering front (polygonal weathering, tafoni,
gnammas, pseudokarren, caves, and so forth) (Twidale, 1982a; Thomas, 1994; Vidal
Romanf and Twidale, 1998). It also explains the genesis of stepped slopes (Twidale and
Bourne, 1975, 1978) and mushroom profiles (Twidale, 1962), which together with tafoni
lines at different heights in Ayers Rock (Uluru) (Twidale, 1978), indicate an older
Figure 21.41. Embryonic dome forms on a savanna region. Masai Mara, Kenya.