CAMBRIDGE GEOGRAPHY A2 REVISION - TROPICAL ENVIRONMENTS: TROPICAL LANDFORMS. Contains: tors, inselbergs, pediplanation, peneplanation, etchplain, tower karst, cockpit karst, basalt surface of weathering, saprolite, relict features, duricrusts, topic summary, additional work, suggested websites.

1. A2GEOGRAPHYREVISION
TROPICAL ENVIRONMENTS
7.3 TROPICALLANDFORMS

2. KEYTERMSANDDEFINITIONS
Tors are ridges or piles of spheroidically weathered boulders that have
their bases in the bedrock and are surrounded by weathered debris.
Inselbergs are any isolated hill or hills that stand prominently over a
level surface.
Pediplanation is the extension of plains at the expense of interfluves
through the process of parallel retreat.
Peneplanation is the formation of an area of low relief (peneplain)
separated by low erosional residuals.
Etchplain is an area of stripped and exposed unweathered bedrock.
Tower karst refers to upstanding rounded blocks of limestone set in a
region of low relief.

4. KEYTERMSANDDEFINITIONS
Cockpit karst is a characteristic of tropical areas. It is a landscape pitted
with smooth-sided soil-covered depressions and cone-like hills.
Basal surface of weathering, also known as the weathering front,
represents the depth to which rocks have been weathered; i.e. the
boundary between the weathered rock (saprolite) and the solid
unweathered rock.
Saprolite is weathered rock.
Relict features are landforms formed under conditions not currently
experienced.
Duricrusts are concentrations of minerals such as iron, aluminium,
silica and calcium carbonate within the zone of weathering.

6. TOPICSUMMARY
Tropical landforms are diverse and complex.
● In the humid tropics, the availability of water and the consistently
high temperatures maximise the efficiency of chemical weathering.
● The ‘weathering front’ or ‘basal surface of weathering’ between
sound rock and saprolite (weathered rock) may be very irregular.
● Typically, deep weathering occurs down to 30–60 m.
● Duricrusts are concentrations of iron (ferricrete), aluminium
(alcrete), silica (silcrete) and calcium carbonate (calcrete) found
within the zone of weathering.
● A laterite horizon is formed under the surface when iron and
aluminium oxides are concentrated there.

8. TOPICSUMMARY
A peneplain is an area of low relief, separated by low erosional
residuals (monadnocks).
● Pediplanation proposes the extension of plains at the expense of
interfluves through the retreat of slopes though parallel retreat.
● An etchplain is an area of stripped and exposed unweathered
bedrock.
● An inselberg is any isolated hill or hills that stand prominently over
a level surface.

10. TOPICSUMMARY
Tors are ridges or piles of spheroidically weathered boulders that have
their bases in the bedrock and are surrounded by weathered debris.
● An inselberg or bornhardt is characterised by steep slopes and a
convex upper slope.
● There are two major landform features associated with tropical
karst: cockpit karst and tower karst.
● Underground karst features include caves and tunnels formed by
carbonation-solution and erosion by rivers.

11. ADDITIONALWORK
1. Describe and account for the main types of weathering in tropical
environments. How effective are they and why?
2. Compare and contrast the processes of pediplanation, peneplanation
and etchplain formation. Comment on the landforms they produce.
3. Describe and explain the formation of tors and inselbergs.
4. Account for the features associated with tropical karst.
5. Explain the term ‘basal surface of weathering’. How is the
development of tropical landforms influenced by the basal surface of
weathering?
6. To what extent are tropical landforms relict features?

12. SUGGESTEDWEBSITES
www.rswa.org.au/content/work/journals/PDF/80(3)/80(3)campbell.pdf
for an article on granite landforms in tropical environments (including
photographs).
www.geomorph.org/gt/regional/nam.html for granite inselbergs of the
central Namib desert.
www.tourmalaysia.com/category/sarawak/sarawaktoursit-spot/mulu-
national-park-sarawak-toursit-spotsarawak-2 for Gunung Mulu
National Park, with video. This is one of the world’s most intensively
studied areas of tropical karst.
www.agc.army.mil/research/products/desert_guide/lsmsheet/lsduri.ht
m for information on duricrusts.