GO 111 Background to Geomorphology
By Ms Esther Gabriel
• Department of Geography and Environmental
Studies (GES)
•College of Humanities and Social Sciences (CHSS)
•The University of Dodoma
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INTRODUCTION
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GO 111: COURSE SUMMARY
1.Internal Earth or Geomorphic processes
and landforms: Crustal rearrangement
(plate tectonics), Vulcanism (Intrusive and
Extrusive), Diastrophism (Folding and
Faulting), Rock forming processes.
2.External Earth or Geomorphic processes
and landforms: Weathering, Mass wasting,
Erosion and deposition, Fluvial (running
water and underground water), Aeolian
(wind), Glacial (moving ice), Waves ad
currents (ocean).
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Topic 3: External Earth Processes
and Landforms
3.1 Weathering
3.2 Mass wasting
- Field description of the above.
3.3 Erosion and deposition
3.3.1 Fluvial (running H2O & underground H2O)
3.3.2 Aeolian (wind erosion and deposition)
3.3.3 Glacial (moving ice)
- Field description of erosion and deposition
processes and landforms
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DEFINITIONS
• Topography or landforms —the surface
configuration of Earth.
• A landform is an individual topographic
feature, of any size. e.g. A cliff or a sand
dune; a peninsula or a mountain range.
• The plural— landforms—is less restrictive
and is generally considered
synonymous with topography.
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DEFINITIONS
• Geomorphology—the study of the
characteristics and development of
landforms.
Etymological definition:
• Geomorphology is derived from Greek
• Ge - 'earthʼ morphe - 'formʼ
• logos - 'discourseʼ or ‘study’
Thus geomorphology is the study of earth
forms.
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DEFINITIONS
Geomorphology
• The word “geomorphology” was first
coined and used between the 1870s and
1880s to describe the morphology of the
surface of the Earth.
• But it was popularized by William Morris
Davis who proposed the “geographical
cycle” also known as “Davis cycle”.
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DEFINITIONS
What is geomorphology in simple words?
• Geomorphology
is
the
study
of
landforms, their processes, form and
sediments at the surface of the
Earth (and sometimes on other planets).
• Study includes looking at landscapes to
work out how the earth surface
processes, such as air, water and ice,
can mould the landscape.
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Geomorphological investigation
• Geomorphological Investigations
may be directed towards:
a. Reconstructing past processes
and landform changes,
b. Understanding present-day
processes and landform changes, or
c. Anticipating future processes and
landform changes.
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STUDY OF LANDFORMS
• About 70% of our planet is covered by the
ocean, and
• Earth includes more than 150 million
square kilometers of land—the
continents and islands of the World (that
are covered by vegetation, soil, or the
works of people).
– We are studying all of the above
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BASIC ELEMENTS IN THE ANALYSIS OF
LANDFORMS
Structure refers to the
nature, arrangement, and orientation of
the materials making up the landform
being studied.
• Structure is essentially the geologic
underpinning of the landform. Is it
composed of bedrock or not; of what
kind? etc.
1.
Structure:
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BASIC ELEMENTS IN THE ANALYSIS OF
LANDFORMS
2.
Process: Process considers the
actions that have combined to produce
the landform.
A variety of processes—geologic,
hydrologic, atmospheric, and biotic—may
be at work shaping the features of the
lithospheric surface, and their interaction
is critical to the formation of the
feature(s).
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BASIC ELEMENTS IN THE ANALYSIS OF
LANDFORMS
3. Slope: Slope is the fundamental
aspect of shape for any landform.
• The angular relationship between a
surface and the surrounding landscape
is essentially a reflection of the
contemporary balance among the
various components of structure and
process.
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BASIC ELEMENTS IN THE ANALYSIS OF
LANDFORMS
4. Drainage: Drainage refers to the movement
of water (from rainfall and snowmelt), either
over Earth’s surface or down into the soil and
bedrock.
• Considered a basic element in landform
analysis with its significant ramifications of
slope wash, streamflow, stream patterns, and
other aspects of drainage.
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BASIC ELEMENTS IN STUDY OF LANDFORMS
• After identifying the basic elements, the
geographer seeks to answer the fundamental
questions of any geographic inquiry:
• What? The form of the feature or features
• Where? The distribution and pattern of the
landform assemblage
• Why? An explanation of origin and devt.
• So what? The significance of the topography in
relationship to other elements of the
environment and to human life and activities.
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DENUDATION
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DENUDATION
• Lowering of continental surfaces.
• The overall effect of the disintegration,
wearing away, and removal of rock
material.
• Denudation is accomplished by the
interaction of three types of activities
weathering, mass wasting and erosion.
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DENUDATION
1. Weathering: Breaking down of rock into
smaller components by atmospheric and biotic
agents.
2. Mass wasting:
Relatively short-distance
down-slope movement of broken rock material
under the direct influence of gravity.
3. Erosion: The removal, transportation, and
eventual deposition of fragmented rock material
over wider areas and sometimes to greater
distances than is the case in mass wasting.
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Weathering
 Breakdown and decomposition of
earth material (rocks).
 Physical and chemical disintegration
of rocks:
- Destabilize surface materials for
eventual
removal
by
erosive
processes.
- Influences soil devt. and texture
- Releases chemical compounds
ready for biological processes.
Weathering
Weathering occurs in two ways:1. Physical weathering
or
mechanical weathering
2. Chemical weathering
1. Physical weathering or
mechanical weathering
• Simply breaks large pieces into
smaller ones.
• Involves the sole disintegration of
rock materials and
• No change in the chemistry of the
material being altered.
2. Chemical weathering
• Involves the decomposition of
rocks and sediment.
• Decompose definition.
- Decay, break into component
elements or simpler constituents
• A chemical change occurs and a
new product is created from the
material that has undergone
weathering.
Determinants of weathering
Revision Question:
• Identify and explain any five (5)
endogenetic(geological, related
to the rock characteristics) and
any
five
(5)
exogenetic
(pertaining to the external
environment) determinants of
weathering.
1. Physical weathering
• Make smaller pieces out of larger ones; thus
creating additional surface area.
• The additional surface area, makes it easier
for surface materials to chemically decompose
and be eroded.
See the following illustration……..
Impact of physical weathering-increased
surface area
• The shape of the pieces also affects the the
amount of exposed surface area. e.g. Platelike pieces have more exposed surface area
than do block-like pieces.
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Physical weathering processes
Major types of physical weathering processes
a. Weathering by biotic agents
i). Root wedging
ii). Burrowing animals
b. Frost wedging or frost shattering
c. Thermal expansion and contraction
d. Alternate wetting and drying
e. Salt Wedging
f. Exfoliation by unloading or pressure release
Major types of physical weathering
a). Physical weathering by
biotic agents
i). Root wedging
• Plant roots work their way
into rock crevices called
joints.
• As they grow, roots create
pressure on the sides of
the crack enlarging it until
the rock breaks apart.
•
a. Physical weathering by biotic agents
i). Root wedging (cont…)
Problem to home
owners:
If trees grow too close
to a house, roots can
force their way into the
foundation, breaking it
apart, and let water
seep into the
basement.
i. Root wedging
a). Physical weathering by biotic agents
(cont…)
ii). Burrowing animals
• Sometimes are factors in rock
disintegration.
• The total effect of these biotic actions is
probably significant, but it is difficult to
assess because it is obscured by
subsequent chemical weathering.
a). Physical weathering by biotic agents
(cont…)
ii). Burrowing animals
a. Physical weathering by biotic agents
(cont…)
ii). Burrowing animals
a). Physical weathering by biotic agents
(cont…)
ii). Burrowing animals
a). Physical weathering by biotic agents
(cont…)
ii). Burrowing animals
a). Physical weathering by biotic agents
(cont…)
iii). Alternate wetting and drying
•By Lichens: Lichens are primitive
organisms that consist of algae and
fungi living as a single unit.
•Typically they live on bare rock, bare
soil, or tree bark.
•Expansion and contraction of lichens
as they get alternately wet and dry
flake off tiny particles of rock.
Physical weathering processes (cont…)
b. Frost wedging or frost shattering occurs when
water freezes in rock fractures. As the water
freezes it expands putting pressure on the sides
of the crack, enlarging it until the rock breaks
apart.
WATER
ICE
Physical weathering processes
c. Thermal expansion and contraction
Physical weathering processes
c. Thermal expansion and contraction (cont…)
Physical weathering processes
c. Thermal expansion and contraction
Physical weathering processes
Physical weathering processes
c. Thermal expansion and contraction
(not accompanied by freeze–thaw cycles)
 Can weaken rock and cause it to disintegrate.
 The fluctuation of temperature from day to night and
from summer to winter can force expansion when
heated and contraction when cooled weakening and
breaking apart the rock.
 This volumetric variation weakens the coherence of
the mineral grains and tends to break them apart.
eg. In deserts.
Physical weathering processes
iii. Thermal expansion and contraction
Physical weathering processes
iii. Thermal expansion and contraction
Physical weathering processes
d. Alternate wetting and drying
 Causes material to expand and contract, thus
weakening rocks and inducing them to break as
well.
Physical weathering processes
e. Salt Wedging
 Related to frost wedging but much less
significant. Happens when salts crystallize
out of solution as water evaporates.
 In areas of dry climate, water is often drawn
upward in rock openings by capillary action.
 This water nearly always carries dissolved
salts.
 When the water evaporates, as it commonly
does, the salts are left behind as tiny crystals.
 With time, the crystals grow, prying apart the
rock grain by grain, much in the fashion
previously described for freezing water,
although less intensely.
Physical weathering processes
e. Salt Wedging (cont…)
 Along ocean coastlines, salt wedging may
also be a weathering factor.
 Above the tide-line, seawater from ocean
spray gets between mineral grains; after
the water evaporates the growth of salt
crystals can slowly pry off mineral grains.
Physical weathering processes
f. Exfoliation: One of the most striking of
all weathering processes is exfoliation, in
which curved layers peel off bedrock.
 Curved and concentric sets of joints
develop in the bedrock, and parallel shells
of rock break away in succession,
somewhat analogous to the way layers of
an onion separate.
 The sheets that split off are sometimes only
a few centimeters thick; in other cases,
however, they may be several meters thick.
Physical weathering processes
f. Exfoliation (cont…)
 The results of exfoliation are conspicuous. If the
rock mass is large, it is referred to as an
exfoliation dome.
 Overall, especially in regions of exposed plutonic
bedrock, exfoliation tends to gently smooth the
landscape.
 The dynamics of exfoliation are not fully
understood.
 The most widely accepted explanation of massive
exfoliation is that the rock cracks after an
overlying weight has been removed, a process
called unloading or pressure release .
 The intrusive bedrock may originally have been
deeply buried beneath a heavy overburden—
perhaps several kilometers deep. When the
overlying material is stripped away by erosion, the
release of pressure allows expansion in the rock.
Physical weathering processes
f. Exfoliation (cont…)
• The outer layers are unable to contain
the expanding mass, and the
expansion can be absorbed only by
cracking along the sets of sheeting
joints.
• Exfoliation occurs mainly in granite
and related intrusive rocks, but under
certain circumstances it is may also
seen in sandstone and other
sedimentary strata.
Mechanical weathering
NOTE: Mechanical weathering is often, but not
always, accompanied by chemical weathering.

2. Chemical Weathering
•Is the decomposition of rock by the chemical
alteration of its minerals.
• Almost, all minerals are subject to chemical
alteration when exposed to atmospheric and biotic
agents.
• Some minerals, such as quartz, are extremely
resistant to chemical change, but many others are
very susceptible.
• Very few rocks can’t be significantly affected by
chemical weathering because the alteration of even
a single significant mineral constituent can lead to
the eventual disintegration of an entire rock mass.
2. Chemical Weathering (cont...)
•The greater the surface area exposed via
physical weathering, the more effective the
chemical weathering.
•Thus, finer-grained materials decompose
more rapidly than coarser-grained materials
of identical composition because in finegrained materials there is more exposed
surface area.
2. Chemical Weathering (cont...)
•Virtually all chemical weathering requires
moisture.
•Chemical processes operate more rapidly in humid
climates with abundant water than in arid areas.
•Moreover, chemical reactions are more rapid under
high-temperature conditions than in cooler regions.
Thus, chemical weathering is most efficient and
conspicuous in warm, moist climates.
•In cold or dry lands, there is less chemical
weathering and so mechanical weathering tends to
dominate.
2. Chemical Weathering (cont...)
•Some of the chemical reactions affecting rocks are
very complex, but others are simple and predictable.
•The principal reacting agents are oxygen, water,
and carbon dioxide, and the most significant
processes are oxidation, hydrolysis, and carbonation
and hydration.
•These processes often take place more or less
simultaneously, largely because they all involve
water that contains dissolved atmospheric gases.
2. Chemical Weathering (cont...)
•Water percolating into the ground acts as a
weak acid because of the presence of these
gases and of decay products from the local
vegetation; the presence of these impurities
increases the water’s capacity to drive
chemical reactions.
2. Chemical weathering processes
a. Oxidation
•
•
When iron rich minerals oxidize, they produce
the familiar red color found in rust.
Iron oxide produces the red color in soils.
2. Chemical weathering processes
a. Oxidation (cont…)
 Takes place when oxygen dissolved in water
reacts with atoms of metallic elements
abundant in silicate minerals.
 Attacking metals in the soil, oxidation causes
them to rust leaving the soil a brownish red to
red color.
 When oxygen combines with iron, the reddish
iron oxide hematite (Fe2O3) is formed:
4Fe + 3O2
> 2Fe2O3
Iron
+ Oxygen
>
Iron Oxide
(Hematite)
2. Chemical weathering processes
b. Hydrolysis
 Is an exchange reaction involving
minerals and water.
 Free hydrogen (H+) and hydroxide (OH)ions in water are able to replace mineral
ions and drive them into solution.
Changing the mineral's atomic structure.
 It is a process whereby silicate minerals
like potassium feldspar are weathered and
a clay mineral is formed.
2KAlSi3O8 + 2H+ + 9H2O- > Al2Si2O5(OH)4
+ 4H4SiO4 + 2 K2+
2. Chemical weathering processes
c. Carbonation
 Carbonic acid action involves combination of
carbon dioxide and water.
 Though present in pure water, carbon dioxide
dissolved in water provides ions that produces
free hydrogen.
 Carbon dioxide in the atmosphere combines with
rain water to form carbonic acid (H2CO3)
i.e H2O + CO2 -> H2CO3
 Though weak, when carbonic acid is combined
with a mineral like calcite (CaCO3) common to
limestone, calcium and bicarbonate ions are
released and carried off by groundwater.
CaCO3 + H2CO3 -> Ca+2 + 2 HCO-3
2. Chemical Weathering (cont...)
d. Biological Weathering
Plants frequently and animals occasionally contribute
to weathering called biological weathering.
i. Animals/ organisms
• Lichens: are primitive organisms that consist of
algae and fungi living as a single unit.
•Typically they live on bare rock, bare soil, or tree
bark.
•They draw minerals from the rock by ion exchange,
and this leaching can weaken the rock.
2. Chemical Weathering (cont...)
Lichens
LAKE DISTRICT
IRELAND
UNITED
KINGDOM
Rocks covered with multicolored lichens in the Lake
District of England.
Physical or Chemical Weathering?
NOTE:
e. Hydration involves the absorption of water like
which occurs during the conversion of hematite to
limonite:
2Fe2O3 + 3H20 -> 2Fe2O3 . 3H20
 Some geoscientists question whether hydration is
a true chemical weathering process because the
process is readily reversible and the new product
is not chemically different from its precursor.
 Some would rather call hydration a physical
weathering process.
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Differential Weathering
•All rock does not weather at the
same rate or to the same extent.
•Some rocks are relatively weak and
easily weathered, whereas other kinds
of rock are strong and more resistant to
weathering.
•This brings us to the concept of
differential weathering.
Differential Weathering
•Exposures of weaker rock are more obviously
susceptible to mass wasting and erosion than
exposures of stronger rock.
•The strength of the rock and the local
environment strongly influences differential
weathering.
•e.g. Rock that resists weathering in an arid
environment might actually be relatively “weak” in
a humid environment.
Climate and Weathering
• Generally,
weathering, particularly chemical
weathering, is enhanced by a combination of high
temperatures and abundant precipitation; whereby,
the moisture is usually more important than
temperature.
- For example, in most desert regions, because of
a general lack of precipitation, mechanical
weathering may be more conspicuous than
chemical weathering.
Climate and Weathering
•The climatic regime significantly influences
patterns of soil development.
- There are many variations in the connection
between weathering and climate.
Note: All else being equal, the depth of active
weathering tends to be relatively shallow in regions
of tundra and desert but relatively deep in regions
of tropical rainforest.
Weathering
The spatial variation of climate and organisms
play a significant role in the weathering of earth
materials.

Dry locations tend to be dominated by
physical weathering and moist places by
chemical weathering.
The type of earth material available also
determines the amount of weathering that might
take place. E.g. Limestone is easily broken down
where abundant rainfall and high temperatures
prevail. However, limestone will remain intact in dry
locations.
ASANTENI