Plains – the expected granite form - Landforms and Geology of Granite Terrains - page 69

(a)

(b)

Figure 4.7. Isolated granite platforms, (a) the exposed crests of domes in western Pilbara, Western Australia.

(b) In the piedmont of Ampidianambilahy, Andringitra Massif, Madagascar.

related to scarp-foot weathering has taken place, it amounts at most to only a few tens of metres
(see Chapter 6) whereas pediments may be scores, or even a few hundreds of metres across. The
residual boulders standing on some pediments are flared, suggesting that they were weathered dur-
ing a period of topographic stability when the weathering front was lowered (Chapter 8). Then fol-
lowed a phase of erosion, during which the friable grus was evacuated to expose the boulders
shaped by subsurface moisture attack. Thus, on the Waulkinna pediment, and at Houlderoo, both
granitic and both located in the southern piedmont of the Gawler Ranges, South Australia, the
evidence suggests that there has been a lowering of the surface by some 2 m ( Fig. 4.8) .
The concentration of moisture in the scarp-foot zone has led to the development of moats of
especially deep weathering - incipient scarp-foot depressions - as well as flared forms and cliff
foot caves or tafoni, all of which argue relative stability of marginal slopes and weathering zones.
It is true that, in appropriate settings, wind-driven waves and associated marine agencies, frost action
and glaciers have caused local wearing back of basal slopes and escarpments, but such activities
are specific to certain environments, with which pediments are not commonly associated.