Geography
seminar at
UMSS
Namugongo
By: Kembabazi Gloria and
Kisakye Irene
QUESTION
EXPLAIN THE INFLUENCE
OF WEATHERING
ON LANDFORM
DEVELOPMENT
IN EAST AFRICA.
QUESTION APPROACH:
INTRODUCTION:
Define weathering, identify the types
of weathering, effects……
MAIN BODY(EXPLANATIONS and ILLUSTRATIONS):
Explain the features formed under
each type giving clear examples in
East Africa
CONCLUSION:
Write a conclusion
DEFINITION
Weathering is the chemical
decomposition of rocks or
mechanical fracturing and
break down of rocks to form
small particles at or near the
surface of the earth insitu.
There are two main types of
weathering: Physical and Chemical
• Physical involves rock
disintegration without
changes in chemical
composition.
• It is also known as mechanical
Weathering
• Chemical is one that involves
changing the chemical
composition of the rocks and
some of the rocks may suffer
decay.
• Biological weathering involves
plants and animals and may aid
the processes of physical and
chemical weathering.
Physical weathering processes
includes:
• granular disintegration,
• block disintegration,
• crystal growth,
• pressure release,
• freeze and thaw action and
• aridity shrinkage.
Chemical weathering
processes includes:
• hydration,
• oxidation,
• hydrolysis,
• carbonation,
• chelaition,
• spheroidal and solution.
LATERITE FORMS:
These are wide spread rock like
fossilized crusts in tropical
Africa.
They are relic of ancient phase
of soil formation composed of
highly weathered rock minerals
concentrated in thick layers(2m12m thick).
These include;
ferricretes-iron and silica,
silicrete(bauxite-aluminium)
for example in Buganda,
they are about 9meters
thick.
• Cemented by wetting, drying
and heat to form hard rock.
Iron compounds are organically
produced in swamps by
capillary action on rotten or
decayed rock for example
• Conditions: low relief, heavy
rainfall, dry season, top soil
removal, flat-topped hills.
INSELBERGS:
These are isolated hills
that stand prominently
above a leveled surface.
They are common in arid
areas like Nakasongola,
Mubende, Soroti in Uganda,
Voi in Kenya and Sukuma
land in Tanzania.
AN INSELBERG IN VOI-KENYA
a)Tors:
These are ridges of
spheroidically weathered
boulders normally of
granite and surrounded by
weathered debris due to
chemical rotting along
joints below the surface.
At high points they are
called skyline tors and on
hills and depressions,
sub-skyline tors they may
be 20meters to 30 meters
thick and 3m to 8m in
diameter.
b)Castle kopjes:
These are rock piles that have
suffered little spheroidal
weathering. They are steep sided
massive crystalline boulders that
are cube like and blocky.
They have a castle like profile
and kopjes means hill as
illustrated below:
The are found in the dry corridor
of Tanzania, North eastern
Kenya, Teso, Lango and North
eastern Uganda.
c) Bornhardt (domed inselberg)
They are prominent dome
shaped hills in platonicigneous or metamorphic rock
areas.
They are common in humid
or semi desert areas for
example inselberg corridor in
Tanzania.
• The stripping exhumation
theory explains that they
are formed by the
increased removal of the
regolith by weathering
leaving isolated hills.
• The Lester king’s scarp
retreatment theory
explains that they were
formed by lateral
retreatment of valley side
leaving a remnant
inselberg.
ETCH PLAIN
This is an extensive rock
studded plain common in
tropical and semi arid region.
It is formed at two levels,the
surface and some level below the
surface.
It is formed by the gradual
lowering and stripping of the
regolith.
The different types of
etch plains include:
• laterised,
• dissected,
• partly stripped,
• stripped and incised.
KARST LANDSCAPE
These are found in lime stone and
dolomite areas for example Hima,
Tororo, Fort Portal, MombasaBamburi.
These include:
a) Cave:
is a chamber in the rock found
underground. It is formed by
solution when ground water
dissolves and forms cavities by
attacking joints and bedding planes
together with mechanical erosion by
underground streams and occasional
rock collapse.
Stalagmite:
is a mass of crystalline calcium
carbonate growing upwards
from the floor of the cave. It
forms as water sips through
cracks in the rocks and drips
from the cave ceiling to the
floor.
b)
Stalagmite:
c) Stalactite:
this a mass of crystalline
calcium carbonate hanging
down from the roof of the
cave like Nyakasura.
Stalactite
d) Pillars:
this is when a stalagmite and
stalactite meet either accidentally
or the stalagmite grows upwards
until it reaches the ceiling for
example in Kiomoni and kange on
either side of Mukulumuzi valley
in Tanzania.
Pillar
e) sinkholes:
these are deep holes with nearly
vertical sides leading to an
underground cave system , as a
result of surface solution and
subsurface collapse. It is a sink
where a river disappears
underground and is lost from the
surface.
Sinkhole
f) Doline:
Is a shallow depression or hollow
with gently sloping sides and
circular in a plane, originating
from water percolating
underground at the intersection
of major joints.
General photograph
General diagram of Karst landscape
EXFOLIATION DOME:
This is a rounded rock surface
formed when thin layers peel off
a rock for example in
Nakasongola ,Kumi in Uganda and
Serengeti in Tanzania.
Others include
Limestone Gorge
Grikes and clints on limestone
pavements
Cliffs and Uvalas
Kembabazi Gloria &
Kisakye Irene Henrietta