Geology Reference
In-Depth Information
(a)
(b)
Figure 7.18.
(a) Dissected granitic terrain in Sabah, East Malaysia (Photobank, Singapore). (b) Boulder field.
The all slopes topography typical of many parts of the humid tropics can be interpreted as due to
fracture-controlled stream incision, with the rate of downcutting controlled by local and regional
baselevels, but almost everywhere less than the rate of weathering. As noted (Chapter 6), most born-
hardts are two-stage or etch forms, and nubbins are bornhardts the outer sheets of which have been
broken down, mostly below the land surface, to blocks and boulders. They are typical of monsoon
areas and reflect the rapidity of weathering in such areas. The granitic ridges and ranges of the humid
tropics can be regarded as elongate bornhardt complexes which have been converted to nubbins.
However, despite stream incision, and reflecting the typical high rate of weathering, they still carry a
regolithic cover. They are two-stage forms, the development of which has been arrested at stage one.
Of the minor forms found on granite outcrops (see Figs 7.18b and c and Chapters 8-11 inclu-
sive), Rillen are common both on the coast and inland, especially in cleared areas. Rock basins and pit-
ting are well-developed and split rocks are known. Neotectonic forms are also notably absent though
this may be more apparent than real. Such forms as A-tents, or pop-ups, may be developed at the
weathering front, at the base of the regolith, but not be exposed save in special and rare circumstances.
