Page 178 - Fundamentals of Geomorphology

WEATHERING AND RELATED LANDFORMS 161

TA
TA
TA
TA
TA
TA
TA
TA
TA TA
TA
TA

TA
TA
TA
TA
Allitization Podzolization
Kaolinization Ice cover
Tectonically
Smectization TA
TA
active areas
Little chemical weathering – hyperarid
Figure 6.4 The main weathering zones of the Earth.
Source: Adapted from Thomas (1974, 5)

associated with the tropical rainforest of the Amazon Within each of the first five zones, parochial varia-
basin, Congo basin, and South-East Asia. tions arise owing to the effect of topography, parent
2 The kaolinization zone accords with the seasonal rock, and other local factors. Podzolization, for example,
leaching regime of the seasonal tropics and is associ- occurs under humid tropical climates on sandy parent
ated with savannah vegetation. materials.
3 The smectization zone corresponds to the subtropi-
cal and extratropical areas, where leaching is relatively The effects of local factors
weak, allowing smectite to form. It is found in many
arid and semi-arid areas and in many temperate Within the broad weathering zones, local factors –
areas. parent rock, topography, vegetation – play an impor-
4 The little-chemical-weathering zone is confined to tant part in weathering and may profoundly modify
hyperarid areas in the hearts of large hot and cold climatically controlled weathering processes. Particularly
deserts. important are local factors that affect soil drainage.
5 The podzolization zone conforms to the boreal In temperate climates, for example, soluble organic acids
climatic zone. and strong acidity speed up weathering rates but slow
6 The ice-cover zone, where, owing to the presence of downtheneoformationofclaysorevencausepre-existing
ice sheets, weathering is more or less suspended. clays to degrade. On the other hand, high concentrations