GEOGRAPHY
GRADE 11
WEEK 5 - SLOPES
LESSON 5: Overview of South Africa’s Topography
You must use these Resources:
You must know:
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Key Terms: altitude; physiographic regions;
plateau; escarpment; topography; basin; slope;
plain and cross-section etc.
what South Africa’s topography looks like.
where the important relief features are located.
how to calculate vertical exaggeration of cross
sections and the gradient of a slope.
LEARNER TASK:
Lesson on page 3 below
Textbook:* Topic 2 – Geomorphology
Atlas: physical map of South Africa
Topographical maps; orthophoto maps
Google Earth images
Task given below
Textbook: Additional activities*
Use the information on Page 3 and your textbook to complete the
following task in your workbook.
5.1 Find a physical map of South Africa in your atlas, textbook or click on this link for a map
(https://tinyurl.com/yd6n4vjt). Use the following base map of South Africa to complete this activity.
Scale 1: 26 000 000
INSTRUCTIONS:
5.1.1 Label and indicate the following:
(a) the Central Plateau
(b) the Escarpment and plateau slopes
(c) the coastal plains and coastline
5.1.2 Draw and label the following regions using
an area symbol and different colours:
(i) the Great Karoo
(ii) the Kalahari basin
(iii) the Cape fold mountains
(iv) the Central Highveld
(950 m)
(46 m)
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The following cross-section of the landscape of South Africa is from the west coast through Springbok to
Durban on the east coast. Study the profile and answer the questions.
1 cm represents 1000 m
5.2
N
M
Scale 1:10 000 000
(Cape Farm Mapper image: 2020-03-27. Constructed by Mike Eksteen and Andre Jacobs)
5.2.1 Indicate and label the following features on the cross-section:
the central plateau, the escarpment, the plateau slopes, the coastal plains, Springbok and Durban (check
altitude) and the approximate position of the Central Highveld.
5.2.2
the
Refer to the vertical and horizontal scale of the cross-section.
(a) Convert the vertical scale of the cross-section to a ratio scale.
(b) Is the vertical scale or the horizontal scale larger? Substantiate your answer.
(c) Calculate the vertical exaggeration of the cross-section.
𝑉𝑒𝑟𝑡𝑖𝑐𝑎𝑙 𝑆𝑐𝑎𝑙𝑒 (𝑉𝑆)
Formula: Vertical exaggeration = 𝐻𝑜𝑟𝑖𝑧𝑜𝑛𝑡𝑎𝑙 𝑆𝑐𝑎𝑙𝑒 (𝐻𝑆)
(d) Explain how the vertical exaggeration of cross-sections make interpretation of the landscape easier.
5.2.3
Refer to intervisibility between M and N.
(a) Is there intervisibility between M and N?
(b) Give TWO reasons for your answer.
5.2.4
Refer to the gradient of the slope between M and N.
(a) Calculate the vertical interval (VI) between M and N in metres.
(b) Calculate the horizontal equivalent (HE) between M and N in metres.
(c) Use the information in QUESTIONS (a) and (b) to calculate the average gradient between M and N.
Formula: Gradient =
𝑉𝑒𝑟𝑡𝑖𝑐𝑎𝑙 𝑖𝑛𝑡𝑒𝑟𝑣𝑎𝑙 (𝑉𝐼)
𝐻𝑜𝑟𝑖𝑧𝑜𝑛𝑡𝑎𝑙 𝑒𝑞𝑢𝑖𝑣𝑎𝑙𝑒𝑛𝑡 (𝐻𝐸)
(d) Express the answer (ratio) of the gradient in QUESTION (c) in words.
(e) Would the gradient, calculated in QUESTION (c), result in a low or high stream velocity? Give a reason
for your answer.
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Study this topic with the following questions in mind!
TOPIC: Overview of South Africa’s topography
Where is it?
Physiographic Regions of SA (map):
What is it?
Topography
(terrain/landscape) physical (natural) features of an area of land.
Physiographic
region
geographic areas that share distinct properties like landforms, rock
type, and evolutionary history.
Plateau:
- is a high-lying table landscape covering two-thirds of the interior
- consist of both high-lying regions (Central Highveld) and basins
(Kalahari).
- rises to an average height of 1200 m above sea level.
Escarpment:
- surrounds the plateau from Limpopo to the south and then
westwards towards Northern Cape in the shape of an arc.
- divides the central Plateau from the plateau slopes.
- have high mountainous areas.
Plateau
slopes:
- an inclined area between the escarpment and coastal plains
- consist of Cape folded mountains and Great Karoo
Coastal Plains:
- are narrow low-lying areas surrounding the coastline of SA.
What does it look like?
LOCATION:
SA comprises FIVE main physiographic regions:
• SW Cape Fold Mountains
• Coastal Plains
• Interior Plateau with the Great Escarpment around its edges
• Great Karoo and Kalahari Basins
• Central Highveld
W – E cross section of SA through Springbok (point 1) and Pietermaritzburg (point 2) on the map:
WEST
EAST
Land rises gradually
from W to E
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GEOGRAPHY
GRADE 11
WEEK 5
LESSONS 6&7: Slope types, slope elements and slope development over time.
You must use these Resources:
You must know:
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•
•
•
LEARNER TASK:
6.1
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•
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what a slope is (concept).
what the difference between a slope type and a
slope element is.
what slope types and elements look like on
various types of sources and on topographic
and orthophoto maps.
slope elements and characteristics.
Lesson on page 5 and 6 below
Textbook:* Topic 2 – Geomorphology
Atlas: physical map of South Africa
Topographical maps; orthophoto maps
Google Earth images
Task given below
Textbook: Additional Activities*
Use the information on Page 5-6 and your textbook to complete the
following task in your workbook.
Plot the heights of the contour pattern of a Karoo landform below onto the graph to complete the crosssection.
Instructions:
1. Label the slopes:
convex, concave,
uniform, steep and
gentle on the profile.
2. Label the slope
elements:
crest, cliff, talus and
pediment
3. Write down ONE
characteristic of each
slope element in
your workbook.
4. Use a labelled
diagram to explain
the slope
development of a
Karoo landscape.
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Study this topic with the following questions in mind!
TOPIC: Slope types and slope elements
What does it look like?
[AND]
Where is it?
Slope types:
What is it?
Slope:
(gradient/pitch) is the measure of steepness of a landform relative to
the horizontal plane/the rate of rise or fall of a terrain feature.
Slope type:
is part of the topography which is at an angle. Can be described as
curved, inclined surfaces that form the boundaries of landforms like
mountains, plateaus, hills. It can be steep, gentle, convex, concave,
uniform or terraced.
Slope element:
is the form or shape of the slope profile of a landform. It can consist
of a crest, cliff, talus and pediment from top to bottom.
Contours
Side view
Uniform slope
Gradual slope
Slope types and its characteristics:
Concave slope
Slope elements as shown on a Butte:
Convex slope
Steep:
Contour lines are close together.
Gentle:
Contour lines are very far apart.
Uniform:
Contour lines are equal spaced - may be steep or gentle.
Convex:
Contour lines are closer at the bottom, but further apart higher up.
Concave:
Contour lines are far apart at the bottom, but get closer higher up.
Slope elements and its characteristics:
Crest:
at top of hill: convex shape; main processes are weathering & soil
creep
Cliff:
(scarp slope/free face): almost vertical; no material collects; main
process is mass movement
Talus:
(debris slope/scree slope): smooth slope below free face; constant
angle; deposition
Pediment:
a more gentle area at the base of the slope; concave shape; deposition
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Study this topic with the following questions in mind!
TOPIC: Development of slopes over time
What does it look like?
Parallel slope retreat on a Mesa seen from the side:
What is it?
Slope development:
refers to the shaping of slopes over time by a process known as
pararell slope retreat.
Parallel slope
retreat:
• occurs when the steep cliff known as the scarp slope retreats
backward. The pediment increases in length.
• The slope angle and length remain constant over time.
Why is it there?
Causes: climate plays a key role in shaping slopes over time: temperature; wind;
precipitation.
Processes involved: weathering – physical/mechanical weathering (arid climates):
chemical weathering – (humid climates); erosion; deposition.
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Each of the upper parts of the slope retreats (goes backwards) by
the same amount and maintain the same angle.
Therefore, the crest, cliff and the talus retain the same length.
The pediment extends in length and the angle becomes gentler.
Note the smaller circumference of the landform (butte).
This type of slope evolution is called parallel slope retreat.
Parallel slope retreat of a Karoo landscape:
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What impact do slopes have on human activities?
Human-environment interaction:
Environmental: influences on local climate e.g. SH: north facing slopes: warmer, drier,
less dense vegetation; south facing slopes: cooler, more moist, denser vegetation;
Soil erosion caused by soil compaction on trails by people and animals.
Socio-economic: Slope failure caused by quarrying; deforestation; timber extraction;
leads to injury/death; understanding slopes is an important work skill for architects; land
surveyors; engineers; construction of housing, dams; reservoirs; transport and
communication networks; agriculture; livestock rearing
Mesas
Buttes
Pointed - buttes
Designed and compiled by: Penelope Liknaitzky and Hyran Gillion
How do we manage the impact of slopes?
Planning: choices and decisions for building of: settlements, transport and
communication networks, tourist resorts, dams and reservoirs; crop and livestock farming;
afforestation
Problem-solving: choices and decision-making for: slope failure (landslides; rock falls;
falling soil and debris) to determine risk and mitigation measures: stabilising slopes;
monitoring risk; ensuring ongoing maintenance; Example: Chapman’s Peak in SW Cape;
conservation to prevent soil erosion; reafforestation; vegetation buffers; contour
cultivation; economic issues: prevent decrease in: land values; tax revenues; agricultural,
forest productivity; tourist revenues
Acknowledgements: Wilma Mcpherson
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