date: lesson and question 11 dashbo… · lesson 4: droughts and desertification you must know, or...

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CARLETON JONES HIGH SCHOOL

GRADE 11

GEOGRAPHY HOME WORK

EDUCATOR: MRS C GOLDEN DATE: 5 MAY TO 7 JUNE 2020

The following activities must be completed in learner’s workbook after the previous set of work

given.

Please adhere to the dates for each question to prevent falling behind.

DATE: LESSON AND QUESTION 5 MAY LESSON 1 – QUESTION 1

6 MAY LESSON 1 – QUESTION 2


8 MAY LESSON 2 - QUESTION 1
























1 JUNE LESSON 6 – QUESTION 4







KEEP SAFE ! WEAR A MASK ! I MISS YOU ALL !

REMEMBER THAT THE WHATSAPP GROUP IS THERE TO ASK QUESTIONS.

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LESSON 1: THE EARTH’S ENERGY BALANCE

In this lesson focus on summarising what you need to know about:

• Define the term “Energy Balance”

• Clearly understand the concept of the heating of the atmosphere

• Be able to explain the influence of latitude and seasons on the unequal heating of the

atmosphere

• Be able to differentiate between rotation (causing day and night) and revolution (causing

seasons)

• Clearly understand the concept of transfer of energy in the atmosphere

• Clearly understand the concept of transfer of energy by ocean currents and winds

• Use and interpret statistics, graphs, maps and use of an atlas in your explanations

Energy Balance and Heating of the Atmosphere

Earth's Energy balance describes how the incoming energy from the sun is used and returned to

space. If incoming and outgoing energy are in balance, the earth's temperature remains

constant.

• 100% of the energy entering earth’s

atmosphere comes from the sun

(Shortwave radiation)

• 50% of the incoming energy is absorbed by

the earth’s surface i.e. the land and oceans

and most is converted into heat (similar to a

hot plate on a stove) and radiated into the

atmosphere (long wave terrestrial

Figure 1 Earth’s Energy Balance

▪ The mechanics of terrestrial

radiation are Conduction, Radiation,

Convection and Albedo (covered in

Grade 10)

▪ 30% is directly reflected back to

space by clouds, the earth’s surface

and different gases and particles in

the atmosphere

▪ 20% is absorbed by the atmosphere

and clouds.

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The Influence of Latitude and Seasons on the Unequal Heating of the Atmosphere

There is a considerable temperature variation across the surface of the earth.

Have you ever noticed (as in Figure 2) that the size of a spot of light is bigger when the rays hit

the surface at an angle?

Because the Earth is in the shape of a ball, there will be parts of the Earth that receive direct

energy from the sun and other regions of the world that receive indirect energy. This is shown in

Figure 3.

Figure 3

As latitude increases, so the less

direct the sun’s rays are, and the

cooler the surface will be.

As a result of latitudinal differences:

• The mean annual temperature

decreases towards the poles.

• The difference (range) in summer

and winter temperatures increases as

one moves away from the equator.

The difference is greatest at the

poles.

The Earth's Axis is tilted

This is the most important fact about why we have seasons. Because the Earth’s axis is tilted, the

southern hemisphere tilts away from the sun in winter getting only INDIRECT energy from the

sun. Shadows are long and the sun is only up for ten hours in Buenos Aires (Figure 4).

Considerably less insolation is received and consequently winter temperatures are low. In the

summer the southern hemisphere leans towards the sun, causing the sun’s energy to strike more

DIRECTLY. The sun’s energy is more concentrated creating much warmer temperatures.

Shadows are short around noon and the sun is up for 14 hours.

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Figure 4 shows a place on the

same latitude (Allentown) that

has winter during the southern

hemisphere summer and visa-

versa.

As seasons change, so the temperatures will change at any point on the Earth’s surface. The noticeable features are the changing altitude of the sun, the duration of daylight changes and the positions of sunrise and sunset change Figure 4 Opposite Hemispheres,

opposite seasons

Differentiation between Rotation and Revolution of the Earth

Figure 5 Diagram showing the difference between the rotation and revolution of the earth

http://www.webquest.hawaii.edu/kahihi/sciencedictionary/images/revolution.png

The Earth’s Rotation

• Earth spins as it orbits the Sun.

• It takes the Earth 24 hours to make one complete

turn on its axis, so an Earth day is 24 hours long.

• The Sun lights up one half of the Earth, and the

other half is in shadow.

• As the Earth spins we move from shadow to light

and back to shadow and so on.

• It is daytime in South Africa when our part of the

planet is in the lit by the Sun.

• And it is night-time in South Africa when our part

of the planet is facing away from the Sun.

Figure 6 Day and night as seen from space

http://mac.elated.com/wp-content/uploads/earthview.jpg

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The Earth’s Revolution

• The Earth revolves around our Sun.

• It takes just over 365 days (one year) for the

Earth to go around the Sun once.

• The Earth revolves around the Sun at a rate

of about 107 000 kilometres per hour.

• The Earth's revolution around the sun

and the tilt of its rotational axis result in the

seasons.

Figure 7 Revolution of the Earth around the sun

http://www.bbc.co.uk/bitesize/ks3/science/images

/position_of_earth_around_sun.gif

Transfer of Energy in the Atmosphere

Sunlight is more intense at the Equator than at the poles, creating a marked difference in

temperature.

Ocean currents and large ‘convection cells’ in the atmosphere transport heat from the Equator

towards the poles. If there was no way that the heat generated at the equator could be balanced

out by the extremely cold atmosphere at the poles, the Earth as we know it would be

uninhabitable. The two most important mechanisms that transfer heat energy on our planet are

winds and ocean currents.

Close to the Equator, most heat is carried by the oceans, but north and south of about 30 degrees

latitude the atmosphere is responsible for most of the poleward heat transport.

The Role of Winds and Ocean Currents in Energy Transfer

Winds

Figure 8 Average surface temperatures

of the Earth

Uneven global heat distribution gives rise to convection currents in the atmosphere that attempt to equalise heat distribution. Figure 8 shows the surface average temperature gradient (variation) that exists on the planet.

Blue indicates lowest temperatures typical of the Polar Regions while red indicates highest

temperatures found in the Tropical Regions around the equator.

In your next lesson, you will be introduced to the complex wind patterns that exist in the earth’s atmosphere. In simple terms, hot air in the tropical regions rises and moves north and south as upper air winds. The same stream of air eventually reaches the polar region and sinks. This stream of air will return to the tropics as a surface wind.

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As was mentioned earlier, the transfer of heat energy by wind is more efficient closer to the poles.

Figure 9 A simplified model of air circulation in

the atmosphere

http://www.free-online-private-pilot-ground-

school.com/images/circulation-pattern-station.gif

Ocean Currents (Surface and Ocean Floor)

Global winds drag on the water’s surface, causing it to move and build up in the direction that the

wind is blowing.

Ocean currents help to distribute heat around the Earth and circulate massive amounts of warm and cold water. Research on ocean currents have revealed that there is a large scale oceanic circulation system composed of circulating water, much like one would see in the mantle and in the atmosphere.

In the case of ocean currents, surface currents move heated water away from the equator. As this

water reaches the Polar Regions, it cools and sinks to the sea floor (down welling). The current

then returns to the Equator along the sea floor. In the equatorial regions the current rises

(upwelling). This is known as a conveyer belt or thermohaline circulation. “Thermo” relates to

temperature and “haline” to the salt content. Both of these affect the density of the sea water.

Very dense water sinks, while water of a low density rises. The cycle can take up to a 1 000 years

to complete.

Figure 10 Surface Ocean Currents

http://fretzreview.wikispaces.com/file/view/Surface_currents.jpg/30705280/Surface_currents.jpg

Figure 10 shows a

general pattern of

surface ocean

currents. Currents

drawn in red are very

warm. Those in blue

are relatively cold

when comparing

these to the

extremely cold deep

sea currents that flow

along the ocean

floor.

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Figure 11 Deep Ocean Currents

(Global Conveyor Belt

http://www.indiana.edu

/~geol105/images/gaia_chapter

_4/heatpump.jpg

Figure 11 below shows the

conveyer belt of both surface and

sub-surface currents.

Question 1

Refer Figure 1 A, 1B and 1C below showing the influence of latitude and seasons on

temperatures in different parts of the world and answer the following questions.

Figure 1 The influence of latitude and seasons on temperatures in different parts of the world

1.1 Figure 1 A has the effects of latitudinal effects on temperature over the surface of

the Earth. List the letters A, B, C, D, E, and F. Next to each letter, fill in the

approximate line of latitude and the temperature in degrees Celsius. Tabulate your

answer. (12)

1.2 In which temperature zone (colour and temperature) in Figure 1A does South Africa lie?

2 x 2 (4)

1.3 Read the sentence below carefully and fill in the missing word (listed below).

South Africa has a _______________ climate.

http://www.indiana.edu/

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(Tropical, Polar, or Temperate) Give a reason for your answer.

2 x 2 (4)

1.4 Refer to Figures 1B and 1C to answer the following questions:

1.4.1 Refer to the graph of Vostok and write down the month that Vostok experienced its

lowest temperature.

(1)

1.4.2 From your answer to 1.4.1, what was the lowest temperature and what season was

it measured?

2 x 2 (4)

1.4.3 Refer to the graph of Galapagos and write down the month that Galapagos

experienced its lowest temperature.

(1)

1.4.4 From your answer to 1.4.3, what was the highest temperature measured?

1 x 2 (2) 1.4.5 Write down the difference between the lowest temperatures of Vostok in mid-winter and the highest temperature of Galapagos in mid-summer.

1 x 2 (2)

[30]

Question 2

Refer to the diagram below (Figure 2) showing approximate seasonal positions of the sun on its

path during one day.

Figure 2 Diagram showing approximate seasonal positions of the sun

2.1 In which season does the sun travel its longest route from sunrise to sunset? Of what

significance is your answer? 3x 2 (6)

2.2 In South Africa, we are told that the sun rises in the east. Is this strictly true for winter?

Give geographical explanation to substantiate your answer. 3x 2 (6)

2.3 Seasons have an effect on day and night and latitudinal heating of the Earth’s atmosphere.

Write a paragraph to describe each of these. 4 x 2 (8)

2.4 Figure 2.4 is an indication of the effect of seasons on vegetation.

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Figure 2.4 The effect of seasons on vegetation

2.4.1 List the letters A, B, C and D. Next to each

letter, name the season that is depicted.

(4)

2.4.2 Which letters would indicate equal heating

of the northern and southern

hemispheres? (2)

[26]

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Question 3

Case Study: Effect of winds and ocean currents on the transfer of energy in the

atmosphere

Ocean winds and currents affect the temperatures of the Earth. It takes far more energy to change the temperature of water than land or air and water warms up and cools off much more slowly than land or the atmosphere. As a result, inland climates are subject to more extreme temperature ranges than coastal climates, temperatures are moderated near the coast. Over half the heat that reaches the earth from the sun is absorbed by the ocean's surface layer, so surface currents move a lot of heat. Currents that originate near the equator are warm; currents that flow from the poles are cold. The upper 3 metres of the ocean holds as much heat as the entire atmosphere. Ocean currents

and mixing by winds and waves can transport and redistribute heat to deeper ocean layers. It

can reside in this deep reservoir for centuries, which is a stabilizer for the Earth’s climate.

Effects of Ocean Currents

Currents influence the temperature of the coastal regions. Ocean currents have the following

effects:

. Winds blowing over a warm current become warm and at the same time and therefore allow

for more evaporation. Humid winds that blow onshore from the ocean have the effect of cooling.

This is due to the presence of more cloud which blocks radiation from the sun. This would be

the case for Durban and the other coastal cities along our coast. Average temperatures would

be greater without the day of cloud cover over the region.

. Winds blowing over a cold and dry current (as in the Cold Benguela current) cool them, they

help to bring down the temperatures in places, which would have been much hotter. This would

be the case for temperatures measured along the South African coastline. There is little or no

cloud or rainfall. These areas will be on average cooler for their latitudinal position.

When we compare maps of wind and ocean currents at a global scale we see that they are

most of the same features. Note in particular the circulation patterns that form in both wind and

water in each of the world’s ocean basins. The similarity arises from the fact that wind is the

fundamental driver of surface ocean currents.

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Figure 1A – World’s ocean currents

Figure 1B - Average Global wind streams of the world

Conveyer Belt

The whole ocean current system is all linked together in a loop which is called the ocean

conveyer belt.

The red lines represent the warm surface currents. The Gulf stream is the best known of them.

The blue represent the cold currents running in the opposite direction on the sea floor.

Figure 1C – the

Ocean conveyer

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3.1 Differentiate between a Continental effect and a Maritime effect on the uneven heating of

the Earth’s surface 2 x 2 (4)

3.2 Which of the following will heat up and cool the fastest? (Solid/liquid/gas) 1 x 2 (2)

3.3 Winds and ocean currents transfer heat from the equator to the poles. At which latitudes is

wind the most efficient, compared to ocean currents, in moving heat away from the

Equator? 2 x 2 (4)

3.4 In which latitudes would the role of wind and ocean currents be similar.

Give a reason for your answer. 2 x 2 (4)

3.5 Where is most (over half) of the sun’s energy stored? Of what significance is this? 2 x 2 (4)

3.6 Briefly explain the effects that the two ocean currents flowing on the east coast and west

coast of South America (Southern hemisphere) have on the uneven heating of the two

coastlines respectively. In addition, name the two currents. 6 x 2(12)

3.7 Refer to Figures 1 A and 1 B and answer the following questions:

3.7.1 In which direction are the gyres (circular currents) rotating at P and R? 1 x 2 (2)

3.7.2 From your answer to Question 1.6, in which direction are southern hemisphere

gyres circulating? 1 x 2 (2)

3.7.3 Refer to both Figure 1 A and 1 B. List the letters showing the major gyres and match

them up with the wind circulation patterns in numerals. (4)

3.7.4 In which hemisphere are the wind circulation patterns more a duplicate of the ocean

gyres? Why would this be the case? 2 x 2 (4)

3.8 Explain how the word thermohaline. 1 x 2 (2)

3.9 Explain the role that the “thermohaline” current plays in regulating temperatures on the

Earth. 2 x 2 (4) [48]

• On a global scale the ocean conveyer belt originates in the North Atlantic, where cold,

salty water sinks and forms North Atlantic Deep Water.

• This water flows southward all the way to the Southern Ocean, where it turns eastward.

• As this deep ocean current travels east, some of it branches northward into the Indian

Ocean, while the rest continues on into the Pacific Basin before turning north.

• Along the way, this deep ocean water mixes with other deep water, gradually becoming

slightly warmer and less salty.

• In the North Pacific and the northern Indian Ocean, upwelling draws the water back to

the surface.

• Surface currents then drive the water back to the west at low latitudes.

• As the water warms, evaporation increases its salinity.

• After rounding the southern tip of Africa, the water crosses the Atlantic and heads north

as the Gulf Stream.

• The Gulf Stream returns to the North Atlantic, where the warm, salty water cools, sinks,

and starts the cycle over.

• This cycle take about 1000 years to complete one loop.

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LESSON 2: GLOBAL AIR CIRCULATION


The mechanics present to create global wind and pressure belts as a response to the unequal

heating of the atmosphere

The relationships between air temperature, air pressure and wind

The direction of movement and the speed of winds are related to pressure gradient,

Pressure gradient force, Coriolis force and Geostrophic flow

The link between a stationary earth atmospheric circulation pattern and one that occurs as a

result of the spinning of the earth on its axis

The position and name the major pressure belts of the Earth

The ideas of pressure gradient force and Coriolis force in creating a tri-cellular circulation of

the Hadley, Ferrel and Polar cells and the surface winds that arise

The name and description of the characteristics of large air masses present in the

atmosphere

The origin and effect of winds related to regional (Monsoon) and local air movements (Föhn)

Using and interpreting statistics, graphs, maps and use of an atlas in your explanations

Global Wind and Pressure Belts as a Response to the Unequal Heating of the Atmosphere

As you will remember from lesson 1, Equatorial Regions receive more direct solar radiation than do polar areas. Water maintains its heat, while, land heats and cools in a 1 day cycle. Since water loses heat slowly, more heat is received than lost through radiation in the Equatorial Regions. In the Polar Regions, just the opposite is true. More heat is lost due to radiation than is received. Since the Tropics do not become progressively hotter and Polar Regions colder, there must be a transfer of heat between the two regions or a general circulation. The mechanism that sets up Earth’s general circulation pattern is the latitudinal transfer of heat.

We will deal with the Global Circulation patterns later in this lesson. We need to look at some basics

of pressure and winds which will assist with the understanding of global wind and pressure belts.

Relationships between air temperature, air pressure and wind

The accompanying diagram (Figure 1) will show how variations in temperature cause updrafts,

downdrafts, surface winds and upper air winds. It is important to know that some additional factors

are critical in understanding the circulation of air in our atmosphere. They will be covered in this

chapter as well.

Figure 1 – Circulation as a result of uneven heating

• Warm air is “lighter” than cold air.

• Air that rises on its own (or wants to rise) is known as

unstable air.

• Unstable air is associated with the possibility of cloud

formation.

• Cold air is normally regarded as stable and is an indicator

of cloud free conditions.

• The EXCEPTION is where stable air is forced to rise in the

case of a mountain or surface convergence amongst

others.

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Direction of Movement and the Speed of Winds are Related to Pressure Gradient, Friction,

Pressure Gradient Force, Coriolis Force and Geostrophic Flow

Pressure Gradient and Friction

Pressure gradient affects the wind SPEED

Figure 2 Sea level synoptic chart for

Australia

• Pressure gradient is a HORIZONTAL

CHANGE IN PRESSURE between areas of

high and low pressures.

• Horizontal changes in pressure arise mainly

as a result of uneven heating of the earth’s

surface.

• Remember (from Grade 10) that an isobar is

a line joining places of equal atmospheric

pressure

• Refer to figure 2 that shows two distinct

spacing of isobars labelled A and B

CLOSELY SPACED ISOBARS INDICATE A STRONG WIND. (A)

ISOBARS SPACED FURTHER APART INDICATE A WEAK WIND. (B)

Friction affects the wind SPEED

Figure 3 Effects of friction on wind speeds

If we compare pressure gradients over the land,

ocean and the upper atmosphere as being

equal, the speeds of wind would be different.

The land surface is rough and uneven. Wind

speeds are the slowest here.

The ocean surface has considerably less friction

and wind speeds over the ocean are much

higher with the same pressure gradient.

As one measures wind speeds in the upper

atmosphere, this is regarded as an almost

friction free zone. With the same pressure

gradient (as for land and ocean) the winds

speeds are the greatest and very strong.

Pressure Gradient Force (PGF) and Coriolis Force influence the DIRECTION of Wind

Wind direction is influenced by TWO forces:

1. Pressure gradient force

2. Coriolis force

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Pressure Gradient Force (PGF)

• Pressure gradient force (PGF) acts directly from

a high pressure to a low pressure at 90º to the

isobars.

• It is this force that initiates (starts) the horizontal

movement of air (wind)

Figure 4 – Direction of PGF

Coriolis Force (CF)

• Coriolis force only affects the horizontal

movement of air (wind) ONCE IT HAS

STARTED TO MOVE. (NB. PGF is the

primary cause of air starting to move).

• Coriolis force is set up by the rotation of the

earth and will only react once an air

movements start,

• Coriolis force DEFLECTS (bends) winds

away from the direction from PGF to the left

in the Southern Hemisphere and to the

right in the Northern Hemisphere.

Ferrell’s Law

Standing with your back to the wind, air is deflected to the left in the Southern Hemisphere and to the right in the Northern Hemisphere.

Geostrophic flow Upper atmosphere wind in a friction free zone

Geostrophic winds

These are resultant winds flowing parallel to the isobars found in the upper atmosphere.

Figure 6 Geostrophic flow in the

Southern Hemisphere over South Africa.

Figure 5 Effect of PGF and CF on winds

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• Pressure gradient force (P.G.F.) acts from High to Low Pressure

• P.G.F. acts at right angles to the isobars.

• Coriolis force (CF.) is a deflective force due to the rotation of the earth.

• C.F. will cause winds to be deflected to the right in the Northern Hemisphere and to the left

in the Southern Hemisphere.

• Once an air parcel starts moving, it moves from high to low pressure.

• Once it moves, C.F. acts at right angles to the wind.

• When the C.F. and the P.G.F. are acting in opposite directions, the wind is no longer

deflected.

• This wind is now blowing parallel to the isobars.

• It is known as the Geostrophic Wind.

• Near the surface of the earth, friction causes winds to cross the isobars at an angle.

• In the upper air, friction is less arid therefore a Geostrophic Wind is found.

Global Circulation Pattern of Pressure Belts and Winds

Global Pattern of Pressure Belts

An imaginary uniform Earth with idealized zonal (continuous east to west) pressure belts.

The real Earth has disruptions in its zonal pattern caused by large land masses. These disruptions break up pressure zones into semi-permanent high and low pressure cells. The most permanent belts are found over the oceans

Figure 7 World pressure belts

Pressure Gradient Force and Coriolis Force in Creating a Tri-Cellular Circulation of the

Hadley, Ferrel and Polar Cells and the Surface Winds that arise

Circulation of air in the atmosphere (if the earth were not rotating).

In general circulation theory, areas of low pressure exist over the Equatorial Regions, and areas of

high pressure exist over the Polar Regions due to differences in temperature.

Insolation received by the Earth, and converted to heat, causes air to become less dense and rise

in equatorial areas.

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The resulting low pressure allows the high-pressure subsidence air at the poles to move along the

planet´s surface toward the Equator.

As the warm air flows toward the poles in the upper atmosphere, it cools, becoming denser, and sinks over the Polar Regions. This is the simplistic explanation if the Earth were stationary and not spinning on its axis.

Figure 8 Circulation pattern if the Earth was not spinning on its axis

Tri-cellular circulation of the Hadley, Ferrel and Polar Cells and the surface winds that arise as a

result of the spinning of the Earth on its axis

As has been discussed so far, the force created by the rotation of the Earth is known as Coriolis

force.

It significantly affects air that moves over great distances. The Coriolis force deflects air to the right

in the Northern Hemisphere and to the left in the Southern Hemisphere, causing it to follow a curved

path instead of a straight line.

The amount of deflection increases with increasing

latitude.

The amount of deflection also increases with increasing

speed. The faster the wind speed the greater the

deflection. This changes the general circulation pattern

of the air.

The speed of the Earth´s rotation causes the general

flow (Figure 8) to break up into three distinct cells in

each hemisphere. (Figure 9)

Figure 9 The three convectional cells produced per hemisphere as a result of the Earth

spinning on its axis

Characteristics of the three circulation cells mirrored in the Northern Hemisphere and Southern

Hemisphere.

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Along the equator, moist surface winds converge. Updrafts of moist air cause the development of

cloud formation and it rains a lot

Between 20 and 35 degrees latitude, descending dry and warm air masses give rise to cloudless

skies and desert climates.

Along the polar front, updrafts air masses again give rise to cloud formation and rain.

The three atmospheric cells in each hemisphere are named Hadley 0° - 30° N/S

Ferrel 30°- 60° N/S

Polar 60°- 90° N/S

Figure 10 Tri-cellular Circulation with winds

Hadley Cell

Figure 11

George Hadley identified the

equatorial cells named after

him in 1735 based on wind

direction records from British

ships. It was remarkable

intuition on his part to

extrapolate surface winds

into a three dimensional

model (Figure 11)

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• The tropical winds that blow from the

south east and north east (Trade

winds) to the equatorial area, meet in

the inter-tropical convergence zones

(ITCZ). (Figure 12)

• Much of the air that rises at the

equator does not move directly to the

poles. As a result of Coriolis force

from the spinning of the Earth, down

drafts descends on the 30° latitude to the surface of the earth.

• Some of this air returns to the equator in the form of surface winds. It thus forms part of a

large convection cell which is named the Hadley cell.

Ferrel Cell

• The side of the Ferrel cell which is closest to

the equator produces descending air

creating high pressure cells in both the

Southern and Northern Hemispheres at

approximately 30º N and S.

• The side of the Ferrel cell closest to the poles

in both hemispheres have ascending air

creating a low pressure at the surface.

• The movement of surface winds found in the

Ferrel cell are Westerlies in both

hemispheres

Figure 13 Downdrafts of air at 30º N associated with the Ferrel cell

Polar Cell

There is also a similar third cell, namely the Polar cell,

which forms between 60° and 90° north and south of

the equator. (Figure 14)

• As you will notice at the boundary of the Ferrel and

Polar cells at 60º N, there is convergence on the

surface and uplift.

• This is the area where the Mid-latitude cyclones

form. The section on Mid-latitude cyclones will be

covered in Grade 12.

• At the north and south poles, air subsides creating

a High Pressure

• Surface winds found in the Polar cell are easterly

winds found both in the Southern and Norther

Hemispheres.

Figure 14 Updrafts of air at 60º N associated

with the Ferrel and Polar cell boundary

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Air Mass Characteristics

Large air masses are characterised by their relative temperatures and moisture content.

• Simply, large air masses over land (known

as continental) are generally dry. (C)

• Similarly, large masses over the oceans

(maritime) are generally moist. (M)

• When taking into account that latitude plays

a part in the temperature of air masses, they

will be classified as cold polar (P) and hot

equatorial/tropical (E).

These are abbreviated on maps as:

mP: Maritime Polar

cP: Continental Polar (cA)

mT: Maritime temperate

cT: Continental temperate Me: Maritime Equatorial cE: Continental Equatorial

Regional Air Movements – Monsoon Winds

Monsoon winds are caused by the

migration of the Inter Tropical

Convergence zone and sub-

tropical high pressure belts with

the seasonal migration of the sun.

Monsoon winds affect tropical

coastlines during the summer

Solstice in both the Northern and

Southern hemispheres.

Figure 16 Areas of the world

that experience Monsoons

Africa Monsoon Winds

Notice the north=south migration

of the Inter Tropical Convergence

Zone. This causes a reversal of

winds from summer to winter.

In summer (left), South West

Monsoon (moist) winds blow from

the ocean across West Africa,

bringing rain to the region. In

winter (right), much of the wind

moves from the north east over

the Sahara Desert toward the

ocean. Winter conditions are very

dry.

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Apart from the differing climate between summer and winter, there is a noticeable reversal of winds during the year. Figure 17 African Monsoons

Local Air Movements (Föhn Winds)

This is a general term for warm dry

wind blowing downwards on the

leeward (downwind) slope of a

mountain range. The name Föhn

originates from the name of a hot

dry wind that blows down the

northern side of the Alps.

Notice the much warmer

temperatures are on the leeward

side of the mountain due to the

differing adiabatic cooling and

heating on the windward and

leeward side respectively.

Figure 18 - Föhn and rain shadow effects

In South Africa, we find a similar wind originating from the Indian Ocean. Air rises up the Outeniqua

Mountains producing cloud on the windward (sea side). As the air flows down the other side of the

Outeniqua, Mountains into the little Karoo, air heats up at the dry adiabatic lapse rate. As you can

see from Figure 18, the temperature on the leeward side is considerably warmer than that of the

windward side.

Figure 19 Oblique photo showing the Föhn like wind blowing into the little Karoo.

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Question 1

Refer to Figure 1 Air circulation patterns around high and low pressure centres. (Northern

hemisphere)

Figure 1

1.1 Study Figure 1 carefully. Use

the list of labels below and match

them to the correct letter on the

diagram.

• Updraft

• Downdraft

• Surface wind

• Upper air winds

• High temperature

• Low temperature

• Upper air high pressure

• Upper air low pressure (8)

1.2  How important is the Tropopause when considering climate on the Earth? 2 x 2 (4)

1.3  Which letter indicates a wind that moves in the friction free zone of our atmosphere?

Upper air winds are known by another name. What is this? 2 x 2 (4)

1.4  Is it possible for large cloud systems to form in the area marked D? Give ONE reason for your

answer.

2 x 2 (4)

[20]

Question 2

Refer to the synoptic chart and satellite

photo for Australia (Figures 2 A and Figure

2 B) for 30 December 2007. Answer the

following questions.

Australia Synoptic Chart Figure 1A

23

Australia Satellite Photo Figure 1B

2.1 Locate the area marked K. Is K

situated in the centre of a low

pressure cell or a high pressure

cell?

1 x 2 (2)

2.2 Explain the significance of the

isobar spacing at L and N.

2 x 2(4)

2.3 Would M represent the direction of

pressure gradient force? Give

TWO reasons for your answer.

3 x 2 (6)

2.4  Which hemisphere is Australia located? 1 x 2 (2)

2.5  From your answer to Question 1.4, in which direction will Coriolis force work in relationship

to pressure gradient force? 1 x 2(2)

2.6 Locate the green arrow marked P. Comment on and explain the wind direction indicated by

the green arrow. 4 x 2 (8)

2.7  Refer to the satellite photo (Figure 1 B) and the corresponding synoptic chart of the same

day (Figure 1 A) and answer the following questions.

2.7.1 When looking at D and Q, explain why there is substantial cloud cover as shown on

the satellite photo. 4 x 2 (8)

2.7.2 Account for the lack of cloud cover at F. 2 x 2 (4)

2.8  Answer the following questions based on GIS:

2.8.1 Which of the two Figures (2 A or 2 B) is an example of remote sensing?

Give ONE reason for your answer. 2 x 2 (4)

2.8.2 How many layers of data does Figure 1 B have and how many layers are possible when

using GIS software? 2 x 2 (4)

2.8.3  Is Figure 1 A likely to have Raster or Vector data or both? 1 x 2 (2)

[46]

24

Question 3

Refer to Figure 3 (Semi-permanent pressure systems and winds) and answer the questions that

follow.

Figure 3

3.1 List the letters G, J, K, M, N and P. Next to each letter write down the prevailing winds that would be found in these respective latitudinal belts. In addition, name the deflective force that affects all wind on our earth surface. 7 x 2 (14)

3.2  From your answer to Question 3.1, rank the

latitudinal wind belts in terms of temperature.

3 x 2 (6)

3.3 What role do the major wind belts play in the

uneven heating of the Earth? 2 x 2 (4)

3.4 Name the large convectional cells labelled D, E and F. (3)

3.5  From your answer to Question 3.4, write down TWO characteristics of each cell of the

tricellular model. 6 x 2 (12)

3.6  In what way does the pressure belt over South Africa affect its climate? 3 x 2 (6)

[45]

Question 4

Figure 4 below illustrates the abbreviations used to identify large air masses of differing

temperature and humidity.

Figure 4

4.1 Create a table with TWO columns. Head

each column as Continental and

Maritime respectively. Place the full

names of the air masses in the correct

column. 6 x 2 (12)

4.2  Western California is situated within the

cT air mass. What type of weather

would they expect? Refer in your

answer to temperature, humidity,

diurnal ranges in temperature and

seasonal ranges in temperature.

4 x 2 (8)

[20]

25

Question 5

Refer to the climate data for Bangkok and a map showing

the position of Bangkok in South East Asia. Answer the

questions that follow:

Figure 5A The position of Bangkok in

South East Asia

Figure 5B Temperature and Rainfall Monthly Averages

5.1 In what country is the city of Bangkok found? Write

down the co-ordinates of Bangkok in the correct

manner. (1 x 2) + (4 x 2)(10)

5.2 During which THREE months of the

year does Bangkok receive the least

amount of rainfall. Comment on, and

explain your findings. 3 + 3 x 2(9)

5.3 List the THREE months in which Bangkok receives the highest rainfall. Account for you

findings. 3 x 2 (6)

5.4 Find the month that Bangkok:

a.) has the highest temperature and

b.) has the highest rainfall

(2)

5.5 From your answer to Question 5.4, explain

why the months do not correspond. 2 x 2 (4)

5.6 Which label A or B is India on the blank map?

(1)

[32]

A

B

26

Question 6

Figure 6 shows the effect of temperature variations that occur when air moving from the ocean

moves over a ridge to create a “wet” side and a “dry” (Föhn wind) side. You will also have to

remember the section on orographic uplift you completed in Grade 10.

Figure 5 Orographic effect

6.1 Which side of the mountain is called the windward side? Choose the letter A or B. 1x 2 (2)

6.2 What you think “rain shadow” means. 1x 2 (2)

6.3 Explain the difference between a dry and wet adiabatic lapse rate. 2 x 2 (4)

6.4 Calculate the following:

Moist air from the ocean (25ºC) is forced up the mountain at A. Condensation takes

place at 1000m a.s.l.

(a) What is the temperature at condensation (dew point) level? 2 x 2 (4)

Air continues to rise creating cloud up to the summit of the mountain (2000m).

(b) What would the temperature be at the summit? 2 x 2 (4)

The air, having reached the summit, now descends down the other side of the

mountain to a height of 1000m a.s.l.

(c) What is the temperature of the air at 1000m a.s.l. on the leeward side? 2 x 2 (4)

(d) Is there any difference between the temperatures at 1000m when comparing sides A and B

of the mountain? Explain your findings. 4 x 2 (8)

6.5 Which side of the mountain illustrated by Figure 6 would be most suitable for:

(a) Forestry 1 x 2 (2)

(b) Sheep 1 x 2 (2)

(c) Sugar 1 x 2 (2)

[34]

A B

27

LESSON 3: AFRICA’S CLIMATE REGIONS You must know, or be able to do the following:

Name, understand the characteristics and position of Africa’s major climate regions

Be able to link the African Continent circulation to Global Tri-cellular circulation with

particular reference to areas of uplift (rain) and subsidence (dry)

Identify the major ocean currents around Africa and the influence on climate control

over Africa

Fully understand the processes of El Nino and La Nina and their effects on African

climate

Be able to interpret synoptic charts of South Africa with special reference to air

movements, interpretation of station models and the dominant pattern of High

Pressures that affect the climate. Much of this is a recap from Grade 10.

Characteristics and Position of Africa’s Major Climate Regions

Africa’s position is relatively unique in the sense that it almost has a mirror image of climate zones

to the north and South of the Equator with regard to latitude. The six main climate zones of Africa

are found to the north and south of the equator, namely; Equatorial, Humid Tropical, Tropical and

Semi desert (Sahalian), Mediterranean and Desert.

A climate region is an area with similar temperature and rainfall.

In Grade 10, you learnt about several factors that influence the climate of different places in the

world. These are:

• Latitudinal position

• Altitude

• Distance from the sea

• Prevalent pressure belts

• Ocean currents.

Considering this, Africa has a large variety of different climates.

Map of Africa Climate Zones

Desert

18° - 36° N & S of the Equator

Sub-tropical HP zone

West coast and Continental effect

Cold Canary Current and Cold Benguela Current

Equatorial

10° N & S of the Equator

ITCZ

Continental mainly with west coast warm current

Tropical

(Savannah)

15° to 20° N & S of the Equator

Sub-tropical HP over region in winter

Summer rainfall region prone to droughts and

tornadoes

Large temperature ranges

28

Mediterranean


Situated on the furthest north and south west

margins of the African continent

Winter rainfall brought on by temperate cyclones

(cold fronts)

Maritime

Sahalian

(semi-desert)

20⁰ N of Equator

Transition between Monsoon and

desert zones ITCZ moves N -

summer rainfall

Mainly Continental effect

Humid

Tropical

Transition between Equatorial and Tropical

(Savannah)

Rainfall throughout the year – more in summer

Small variations in temperature

20⁰ - 25⁰ C

High temperatures due to tropical location

Figure 1 Map of Africa showing

the various Climatic regions

Subsidence and Convergence

in Africa

Africa straddles the Equator from

37⁰ N to 34⁰ S. Africa has two

Sub-tropical belts with the ITCZ

somewhat equidistant from the

two high pressure zones.

The ITCZ (also known as the

heat Equator) moves between

the Tropics of Cancer and

Capricorn depending on the

season. This is the area of

massive uplift over Africa and

very high rainfall figures are

measured.

The sub-tropical High Pressure Belt also migrates with the seasonal movement of the overhead

sun. Areas in Africa have their rainfall season when the heat Equator moves into its respective

hemisphere. Figure 2 is more simplified. It shows conditions for an Equinox with the overhead sun

over the Equator.

29

Figure 2 Subsidence and convergence

(link to rainfall) in Africa

The Role of Oceans in Climatic Control in Africa

The ocean covers more than 70 % of the Earth’s surface.

The ocean plays a major role in regulating the weather and

climate of the planet.

Oceans in general have a great influence on rainfall on a

continental basis and an influence on temperatures

along coastal margins.

Figure 3 is an isotherm map that shows ocean temperatures around Africa. If the ocean currents

are superimposed on this map, there will be a striking correlation between the cold ocean currents

and colder waters and warm ocean currents and warm waters.

Isotherm: Line joining places of the same temperatures

Temperature

• The effect of the ocean with regard to temperature

is Maritime in effect.

• Generally, when looking at temperature of oceans

and currents around the coast of

• Africa, there is a dominance of warm water

around the continent.

• The exceptions are the North West and the South

West coastlines, (Cold Canary and the Cold

Benguela currents, respectively.

• Both Mediterranean areas are cooler than

expected due to cloud cover in winter as

cold fronts move through and lessen insolation.

These areas are marked on Figures 3 & 4.

• Since South Africa is surrounded by water masses, all coastline temperatures are

moderated and have small temperature ranges.

Figure 3 Adapted

30

Rainfall

The map of average rainfall over Africa

annually shows a similarity to the maps that

show climatic regions.

The effect of ocean temperatures and

currents has a maritime and continental

effect. This together with the migration of the

“heat Equator” presents a rainfall pattern of

considerably more rainfall over Sub-Saharan

Africa.

Figure 5 Average annual precipitation for

Africa http://www.mapsnworld.com/africa/annual-

rainfall-monsoon-africa.jpg

Processes of El Nino and La Nina and their effects on African climate

The effects of La Nina and El Nino are part of what is called the Southern Oscillation. In Africa,

there are two main areas affected where dry areas receive more rainfall, while, the wet areas

receive less rainfall. The two areas are shown on Figure 6 &7.

The Southern Oscillation originates over the Pacific Ocean. This changes the normal pressure

patterns over the entire Earth’s surface. With changing pressure, winds are affected. Simply, this

means that areas that would normally be moist are dry and visa-versa.

Figure 6

http://kids.mtpe.hq.nasa.gov/archive/nino/elnino.htm l Adapted

http://kids.mtpe.hq.nasa.gov/archive/nino/elnino.html




31

The effects of the Southern Oscillation are graphically represented in Figure 8 where distinct times

of below average and above average rainfall are noticeable.

Figure 8 Rainfall fluctuations in Africa 1900–2000

http://www.unep.org/dewa/africa/publications/aeo-1/fig2a2.htm

32

Interpretation of synoptic charts of South Africa with special reference to air movements

and interpretation of station models

Synoptic Charts

Synoptic charts are drawn 4 times a day at Greenwich Mean Time. We are 2 hours ahead in South Africa. Hence we create synoptic maps at 02:00, 08:00, 14:00 and 20:00. This allows for weather stations throughout the world to collect weather data at exactly the same time. Climatologists are then able to create a global weather picture.

Climate data is collected by land based weather stations, islands (Marion and Gough) and ships.

We are then able to plot the weather conditions to the west, south and east of South Africa.

The major information that can be used from a synoptic chart is:

Isobars that determine wind direction and wind speeds, subsidence and uplift

Station models that measure present weather conditions

Lines of latitude and longitude to show the position of weather phenomena

Observe approaching cold fronts (warm fronts seldom reach South Africa)

Air Movements

The TWO main surface circulation patterns of winds are those of High Pressures

(Anticyclones) and Low Pressures (cyclones), shown by Figure9

These must be understood as to

where winds come from and their

nature. This allows for the

understanding of weather that will

result from these wind patterns.

In lesson 2 Pressure gradient,

pressure gradient force and

Coriolis force were covered with

their impact on wind speeds and

wind direction

The two forces mentioned,

determine the circular flow around

High and Low pressure systems

(Figure 9)

Isobar spacing determines wind

speed.

Closely spaced isobars indicate a strong wind, while, isobars spaced further apart indicate

gentle winds

Air moves from a high pressure to a low pressure

Station Models

It is important to know that a full station model is drawn with the weather observations in

specific positions around the circle

Station models on synoptic charts are too small to show all the weather observations

On Figure 10, the usual station model symbols have been circled

33

Clearly, one cannot just place the 6 circled observations anywhere around the circle. The

one exception is the wind (which is changeable)

Common symbols used on station models are in the table (Figure 11)

Figure 10 Full station model

Source Strahler Physical Geography

Figure 11 Common station model symbols found on a synoptic chart

Source: Future Entrepreneurs

Fronts

• Fronts commonly

affect South Africa

in winter and are

present on South

African synoptic

charts in summer

further to the south

• Warm fronts seldom

pass over South

Africa. Figure 12 3D model of a cold front

34

Cold fronts pass over South Africa leaving very cold sunny days behind In the interior

The fronts approach the country from the west and are responsible for the winter rainfall at

the Cape.

Notice the triangle features on the Earth’s Surface (used on a synoptic chart to show the

position of where the front is positioned on the surface.

Annotated Synoptic Chart

Date & Time

Isobars – lines joining places of the same air pressure

Lines of latitude and longitude – to show position of weather systems

A station model in ( this case a

ship) showing the weather conditions

A Low Pressure system

A High Pressure system

35

Question 1

Refer to the map below (Figure 1 A) showing

Africa’s climate regions and the climate graphs

that match many of the climatic regions (Figures

B – K). Answer the questions that follow:

Desert


Sub-tropical HP zone

West coast and Continental effect

Cold Canary Current and Cold Benguela Current

Equatorial

10° N & S of the Equator

ITCZ

Continental mainly with west coast warm current

Tropical

(Savannah)

15° to 20° N & S of the Equator

Sub-tropical HP over region in winter

Summer rainfall region prone to droughts and

tornadoes

Large temperature ranges

Mediterranean


Situated on the furthest north and south west margins

of the African continent

Winter rainfall brought on by temperate cyclones (cold

fronts)

Maritime

Sahalian

(semi-desert)

20⁰ N of Equator

Transition between Monsoon and desert

zones ITCZ moves N -summer rainfall

Mainly Continental effect

Humid

Tropical

Transition between Equatorial and Tropical

(Savannah)

Rainfall throughout the year – more in summer

Small variations in temperature

20⁰ - 25⁰ C

High temperatures due to tropical location

36

B

C

D E

F G

37

J

1.1 What characteristics do we use to differentiate

between one climatic zone and another? (2)

1.2 Africa is the only continent that can be regarded as

“a mirror image of each hemisphere” with regards

to climate zones. Prove or disprove this statement.

2 x 2 (4)

1.3 Refer to the climatic graphs (Figures B to K). Match any SIX of the climate graphs to the

correct climatic region. 6 x 2 (12)

1.4 Identify the 5 ocean currents that wash the shores of Africa. (5)

1.5 In which season does a Mediterranean climate zone receive its rainfall? 1 x 2 (2)

[25]

Question 2

Refer to Figure 2 A and 2 B that shows El

Nino conditions and La Nina (also known as

“normal”) conditions by some.

2.1 Identify the surface pressures at

A, B and C. In each and give a

reason for your answer. 3 x 2 (6)

2.2 The movements of air at D and E

have names. What are these? 2x2(4)

2.3 Identify the areas that have drought

conditions during an El Nino event by

using Figure 2 A. 1 x 2 (2)

2.4 From your answer, explain the weather

that would be experienced during the

drought conditions brought about by El

Nino. 2 x 2 (4)

2.5 Write a paragraph about the effect that an

El Nino event would affect Southern Africa.

H I

38

In your answer, refer to economic, social and environmental effects. 6 x 2 (12)

2.6 Account for the desert labelled on Figure 2 A. 1 x 2 (2)

2.7 The rainfall indicated over Australia and surrounding islands (Figure 2 B) are Monsoons. Briefly explain the seasonal activity and movement of winds that would cause Monsoons in this area. 5 x 2 (10)

[40] Question 3

Refer to Figure 3 showing a synoptic chart for South Africa. Answer the questions.

Figure 1 Synoptic Chart of South Africa. South African weather services

3.1 Identify the isobar patterns illustrated by the letters on Figure 1. In your answer to this

question, list the following letters and the isobar pattern next to each letter respectively.

(R, S, W X AND Y). 5 x 2 (10)

3.2 Name the two fronts labelled P and Q. List the letters P and Q. Again, next to each, write

down the appropriate answer. 2 x 2 (4)

3.3 Explain how wind speeds would vary in the areas indicated by T and U. 4x 2 (8)

3.4 Write down the direction of the wind found at V, and explain how this wind is generated.

2 x 2 (4)

3.5 The following readings were taken at one of our weather stations yesterday: Air Temperature: 26 °C Dew point temperature: 23 °C Wind speed: 15 knots

Wind direction: WSW Cloud cover: ⅞ Weather: showers Draw a weather station model that reflects these conditions. 6 x 1(6)

3.6 Refer to the synoptic chart showing the west coast of Namibia.

M indicates a ship off the western coastline labelled M. Describe the

weather conditions observed on the day in question. 6 x 1 (6)

3.7 What is the likely pressure of the dotted line (isobar) on the map? (2)

[40]

39

LESSON 4: DROUGHTS AND DESERTIFICATION

You must know, or be able to do the following:

Assess which areas would be prone to droughts and desertification on both a global,

regional and local scale.

Clearly understand the causes of droughts and link back to the El Nino effect on a South

African regional scale

Clearly understand the causes of desertification and the large role that that humans on the

planet have contributed to this problem

Be able to use examples of the effects of droughts and desertification on people and the

environment

Be able to compare differences of vulnerability of different groups of people

Research management strategies using case studies.

Areas at Risk for Droughts and Desertification on a Global, Regional and Local Scale

In this unit we will look at the concepts of

droughts and desertification, the causes of

droughts and desertification and vulnerable

areas on both a regional and a local scale.

Figure 1 Global vulnerability to droughts and desertification

We need to

connect these

ideas with the

effects and

possible

management

strategies that

arise from droughts

and desertification.

Africa is a good

example of great

vulnerability to

drought and

desertification and

a seemingly

inability to manage

these climate

based issues.

A drought means a long period of dry weather during which the lack of rain results in a severe

shortage of water. The South African weather service defines a drought as a period of 12 moths

when total rain received is below 75% of the average.

Desertification is the process whereby land in semi-arid regions become desert, the grasslands

becomes semi-desert and so on. This is a chain reaction of sub-species of fauna invading

40

previously productive land and, in the process, more unproductive land is created. Desertification

goes hand in hand with accelerated soil erosion.

Figure 1 shows global extent of droughts and

desertification. Notice the large area of blue over

South Africa. Figure 2 shows a regional (African)

extent of the problem.

This map shows humanitarian risk hotspots for drought based on the interaction of extreme and significant drought hazard with high overall human vulnerability. Also shown are areas with significant or extreme drought hazard but lower human vulnerability and areas where climate models predict an increase in dry periods, as an indicator of possible future increases in drought risk. Notice that Sub-Saharan Africa is a region designated as one of the most vulnerable areas with regard to vulnerability to droughts and desertification

Figure 2 Drought and desertification risk spots on a regional scale (Africa)

Source: http://www.careclimatechange.org/files/reports/CARE_Human_Implications.pdf

This map shows ‘drought risk hotspots’ based on the interaction of extreme and significant

drought hazards with high overall human vulnerability. Also shown are areas with

significant or extreme drought

hazard but lower human

vulnerability and areas where

climate models predict an increase

in dry periods, as an indicator of

possible future increases in

drought risk.

We will look at a local scale problem

of the eastward migration of the

Kalahari Desert in Southern Africa

(Figure 3)

Figure 3 Eastward migration of

the Kalahari Desert

http://www.kgalagadiphotography.com/resources/SA%20Map%20River%20_HEAT%20%20desert

ific ation.jpg.opt422x297o0,0s422x297.jpg

The geographical position of the Southern Kalahari on the Sub-tropical high pressure belt (latitude

25°-35°S) causes its aridity. High pressure zones like these commonly receive little rain. Air

advected onshore from the west is dry due to a cold ocean current and cold ocean waters.

The semi-desert conditions have almost reached the Witwatersrand. This means that if the area

was left to regenerate natural vegetation with normal rainfall, much of the grassland would have

been replaced by desert scrub.

41

Causes and Types of Drought

Causes of Droughts

This can be triggered by:

• A high level of reflected sunlight, [high albedo]

• An unusual above average and strength of high pressure systems

• Winds carrying continental, rather than oceanic air masses (i.e. reduced water

vapour)

• Ridges of high pressure areas which prevent or restrict the developing of

thunderstorm activity or rainfall over a region.

• Oceanic and atmospheric weather cycles such as the El Niño-Southern Oscillation (ENSO) make drought a regular recurring feature of areas situated in the sub-tropical

high pressure belts of South Africa

Types of Droughts

While droughts can be defined in many ways, three main drought types are commonly identified.

See Figure 4 – a summarised table of the different types of drought.

Figure 4 Types of droughts

http://0.tqn.com/d/weather/1/0/S/9/-/-/climvar.gif

42

Hydrological Drought

Many watersheds experience depleted amounts of available water. Lack of water in river systems

and reservoirs can impact hydroelectric power companies, farmers, wildlife, and communities.

Meteorological Drought

A lack of precipitation is the most common definition of drought and is usually the type of drought

referred to in news reports and the media. Most locations around the world have their own

meteorological definition of drought based on the climate expectations in the area. A normally

rainy area that gets 25% less rain than usual can be considered in a drought.

Agricultural Drought

When soil moisture becomes a problem, the agricultural

industry is in trouble with drought. Shortages in

precipitation, changes in evapo-transpiration, and

reduced ground water levels can create stress and

problems for crops.

Causes of Desertification

Malagasy used to be a rain forest. 10% of the forest remains pictures/tana-

maroantsetra/deforestation_aerial_0068.jpg

The light grey ellipses are those that involve vegetation cover reduction, while the dark grey onesinvolve soil erosion. Human activity can directly trigger desertification such as over farming, excessive irrigation,

deforestation, and erosion. These adversely impact the ability of the land to capture and hold water.

Activities resulting in global climate change are expected to trigger droughts with a substantial

impact on agriculture throughout the world, and especially in developing nations

Figure 5 is a detailed mind map as to how desertification occurs.

Figure 5

The causes and development

of desertification (modified from

Kemp 1994).

43

The Effects of Droughts and Desertification on People and the Environment

There are three main ways droughts impact lives and communities:

Economic impacts of droughts and desertification:

• Losses in the timber industry

• Losses in the agricultural industry

• Losses in the fisheries industry

• Job losses (Figure 6)

• Decrease in the economic growth of a country

• Many of these losses are then passed on to

consumers in the form of higher

commodity pricing

Figure 6 http://2.bp.blogspot.com.jpg

Social impacts of droughts and desertification:

• Increased chance of conflict over commodities, fertile land, and water resources.

• Abandonment of cultural traditions

• Loss of homelands

• Changes in lifestyle

• Increased chance of health risks due to poverty and hygiene issues.

Environmental impacts of droughts and desertification:

• Loss in species biodiversity

• Migration changes of roaming animals

• Reduced air quality

• Increased soil erosion.

• During the monsoon season, areas that depend on the seasonal rains will often

experience drought if the monsoon rains fail

• Once crops fail, famine can become a major problem

• In some African countries, rain rituals are often used to

try and thwart the dry seasons and bring on the rain

• While it is no cure, modern technology has developed

ways to help see potential famine situations as satellites

see famine conditions from space.

Figure 7 Dust storms produce air pollution

http://www.ktar.com/emedia/az/31/3188/318842.jpg

Differences in Vulnerability to Drought

Countries classified as LEDC countries usually have the bulk of their population engaged in

agriculture on a subsistence base. They are reliant on rainfall and do not have dams and irrigation

systems and other means – such as early warning systems from meteorologists to advise them of

an impending drought.

The root causes of vulnerability to drought disasters in South Africa remain low average rainfall,

poverty and development that is not equal. Rapid population growth and urbanisation, tribal

http://www.ktar.com/emedia/az/31/3188/318842.jpg

44

patterns of land ownership, lack of education and subsistence agriculture on marginal land lead to

deforestation and environmental degradation, malnutrition and unemployment, all of which

heighten vulnerability.

Droughts put more people into poverty as they do not have the means to sell some of their

produce. Malnutrition goes hand in hand with drought conditions.

Rivers dry out. These are the source of drinking water for many poor people. There are greater

possibilities of epidemics (like cholera).

Repeated droughts lead to an increase in urbanisation. The cities do not have the resources to

produce housing, jobs, medical facilities, schools and the like.

MEDC countries have farmers that have access to stored water and are able to grow crops that

are more drought resistant. They will have some prior warning about impending drought

conditions.

It is clear that People who belong to the LEDC group are far more vulnerable to droughts and

desertification than people who belong to the MEDC group.

Management Strategies for Droughts and Desertification

Management Strategies for Droughts

Drought is a major feature of the climate of Southern Africa and often has a devastating impact. In

the DROUGHT MANAGEMENT PLAN (DMP) put out by the South African Government, the

issues that should be addressed include:

• Appropriate research plan

• Drought predictions

• Early warning and monitoring systems (satellite remote sensing)

• Decision support tools for drought management

• Establishment of soil-crop-climate norms for agriculture in a reasonably homogeneous farming area (RHFA) in order to grow profitable agricultural products (not necessarily food) • Establishment of norms and standards for grassland and animals in RHFAs, as in

designating herd sizes and selling off livestock before the drought event

• Development of responsive farming plans in the sense that profitable farming is not

exclusively food production, but cash crops that can be profitably sold

• Improvement of research, including that on climate change

• Determination of the impact of global environmental change on drought disaster

characteristics and agricultural production

Source: http://www.nda.agric.za/docs/Policy/2005DMP.pdf Adapted

http://www.nda.agric.za/docs/Policy/2005DMP.pdf



45

Management Strategies for Desertification

The effects of desertification are extremely dangerous

when one looks holistically at the land based ecosystem.

Humans rely on fertile land to produce food for an ever

growing population. At the same time, mass extinction of

land based species is happening daily as deserts move

relentlessly over once fertile land.

The United Nations Convention to Combat Desertification (UNCCD) came into force in1996.

The picture (Figure 8) is a chilling illustration of the dangers of desertification.

Severe soil erosion leads to desertification

As we have seen throughout this topic, soil erosion often goes hand in hand with desertification.

By tackling one, you can affect the other.

Some strategies within the UNCCD are to solve the problems caused by desertification. There has

to an increase in the amount of food that can be grown in areas where people live and farm the

land.

The following problems of desertification can be tackled by:

• Deforestation - Afforestation, that is re-planting trees, especially in shelter belts.

Planting grasses can help stabilise the soil and cut down on erosion by wind and

rain.

• Over cultivation - Using good farming practices such as proper crop rotation and

the use of manure as a fertiliser

• Overgrazing – Control of herd sizes to ensure that the grass is not eaten before it

can be replaced

• Poor irrigation - Make sure the water is not evaporated on a surface which wastes

water and increases its salinity

• Runoff - Terracing the land to slow run off will allow for infiltration and moist soil

• Over population - Control growing populations in marginal agricultural areas by

creating alternatives for

employment.

Question 1

Look at the map showing drought risk over

Africa and answer the questions that follow:

1.1 Name the THREE deserts labelled E, F & G (3)

1.2 Account for the areas H and J as having no

droughts. 5 x 2 (10)

1.3 Name the countries south of area H that have

the highest risk of droughts. (8)

1.4 How would you rate the comparative risk for

drought in South Africa? Give a reason for your

answer. 2 x 2 (4)

1.5 Write a paragraph explaining why Africa as a

continent is the most drought prone in the

World. 4 x 2 (8)

[33]

Figure 8 – desertification caused by severe soil erosion

46

Question 2

Write down the relationship between: 2.1 Amount of rainfall and droughts

(2 x 2) (4) 2.2 Droughts and desertification

(2 x 2) (4) 2.3 Desertification and soil erosion

(2 x 2) (4) 2.4 Desertification and temperature

(2 x 2) (4) 2.5 Desertification and poverty

(2 x 2) (4) [20]

Question 3

Case Study: Desertification of the Southward moving Gobi Desert

Desertification exacerbates poverty, sparks conflict'

United Nations Secretary General Kofi Annan says that desertification is worsening extreme poverty and sparking conflict over dwindling resources, particularly in sub-Saharan Africa (Sahara) and southern Asia (Gobi). "Across the planet, poverty, unsustainable land management and climate change are turning dry lands into deserts," Annan said in a message for World Environment Day.

“There is also mounting evidence that dry land degradation and competition over increasingly scarce

resources can bring communities into conflict,” he said.

Dry lands are found in all regions, cover more than 40% of the Earth and are home to nearly two billion people—one-third of the world population. About 10% to 20% of dry lands are already degraded, which is a “serious obstacle to eradicating extreme poverty and hunger, and is jeopardising efforts to ensure environmental sustainability”, Annan said. Algerian President Abdelaziz Bouteflika said that with deserts growing “at an alarming rate”,

desertification will be “one of the global problems of the 21st century”.

“Deserts are threatening the food security of poor countries, particularly in Africa and southern

Asia, where the number of

malnourished people doubled to 200-

million in 1995 from 100-million at the

end of the 1960s,” Bouteflika said at

an international conference here

marking World Environment Day.

Figure 3a Chain reaction of

desertification

http://local.mg.co.za/article/2006-06-

05-desertification-exacerbates-

poverty-sparks-conflict

By examining satellite data, it is determined that the Gobi is expanding approximately 15.3

km/year. At this rate, China’s capital city (Beijing) will be on the edge of the Gobi within 6-8 years,

and many populated cities in between will be consumed by the desert’s sands. (See Figure 3)

47

Many Chinese officials believe that the idea of Beijing being swallowed by the Gobi in a few years

is “Silly”, but according to the satellite data, if China does not taken drastic action, mass amounts

of people will be displaced, and thirst and famine will be widespread.

The Gobi desert is expanding more than 10,000 square kilometres a year due to over cultivation

and overgrazing. This expansion has already forced migration and threatens thousands more

villages in the Chinese province of Gansu of Inner Mongolia and Ningxia Huizu. China’s sheep,

goat, and cattle populations tripled from 1950-2002, taking a heavy toll on soil quality. Overgrazing

by these animals and an increase in ploughed land has allowed the desert to expand. In Gansu

Province alone, an estimated 4,000 villages are at risk of being buried with sand.

Read the case study ‘Desertification exacerbates poverty, sparks conflict’ ‘as said by Kofi

Annan in 2006 on World Environment day, as well as, an in depth look at the severe desertification

spreading south from the Gobi Desert into China. Answer the questions that follow:

3.1 What are the social impacts that Kofi Annan mentioned in his address? 2 x 2

(4)

3.2 What percentage of the world’s population lives in areas of desertification? 1 x 2 (2)

Figure 3 b Invasion of the Gobi desert in Inner Mongolia

http://img190.imageshack.us/img190/1208/2417908 7 .jp g

Figure 3 c Monthly Frequency of dust storms in the Gobi desert

http://img190.imageshack.us/img190/1208/24179087.jpg





48

3.3 From your answer to Question 3.2, how much of the world’s surface area is desert or turned

into desert? 1 x 2 (4)

3.4 Write a short paragraph on how desertification has impacted food security. 4 x 2 (8)

3.5 On which continent is the Gobi desert? (1)

3.6 Having read the case study, why should the Chinese people living in Beijing be worried?

2 x 2 (4)

3.7 What are the causes and significance of the desertification which is taking place along the

north west border China? 2 x 2 (8)

3.8 During which month are dust storms the most severe and the least severe respectively?

(2)

[33]

Question 4

(Adapted from Gr 11 Exemplar, DBE, Paper 1, Question 1.4)

Study the cartoon on drought in FIGURE 4 and answer the questions that follow.

FIGURE 4

4.1 Define the term drought. (1 x 2) (2)

4.2 State TWO causes of drought. (2 x 2) (4)

4.3 Describe TWO impacts of drought on

people and the environment. (2 x 2) (4)

4.4 Why are developing countries more

vulnerable to drought than developed

countries? (2 x 2) (4)

4.5 Write a short paragraph in which you

explain sustainable strategies at can be

implemented to manage droughts

effectively. (4x 2) (8)

[22]

Question 5


Refer to FIGURE 5 showing desertification in Africa.

49

FIGURE 5: DESERTIFICATION IN AFRICA

5.1 What is desertification?

(1 x 2) (2)

5.2 State ONE way in which

humans contribute to

desertification.

(1 x 2) (2)

5.3 Describe the extent to

which South Africa is

threatened by desertification.

(2 x 2) (4)

5.4 Discuss TWO effects of

desertification on the

economy of Africa.

(2 x 2) (4)

5.5 Write a short paragraph in which you suggest sustainable ways to prevent and reverse

desertification in Africa. (4 x 2) (8)

[20]

50

LESSON 5: GEOMORPHOLOGY I (TOPOGRAPHY)

Key Concepts


• Topography associated with Horizontally Layered Rocks

• Topography associated with Inclined/Tilted Rock Strata

• Topography associated with Massive Igneous Rocks

Topography Associated with Horizontally Layered Rocks

Characteristics and processes associated with the

development of Hilly Landscapes In areas where the climate is arid there is not enough water for sheet-

wash to occur. Water will run unevenly down slopes eroding gullies in

certain places. The slopes are therefore rugged and uneven. There is

little chemical weathering and soils are thin.

Characteristics and processes

associated with the development of

Basaltic Landscapes In areas where the horizontal strata are formed

from lava flows, basaltic plateaus will form. Rivers

will cut into joints and cracks forming steep cliffs

and deep valleys called gorges

A term applied to those basaltic lavas that occur as vast

composite accumulations of horizontal or sub horizontal flows,

which, erupted in rapid succession over great areas, have at

times flooded sectors of the Earth's surface on a regional scale

They are generally believed to be the product of fissure eruptions.

One or a succession of high temperature basaltic lava flows from

fissure eruptions which accumulate to form a plateau. Also known

as flood basalt

51

Characteristics and processes associated with

the development of Canyon Landscapes Canyon landscapes develop where horizontal strata have varying

resistance to erosion

Examples of canyons in South Africa include the Fish River

Canyon and Blyde River Canyon. Canyon landscapes are

characterised by deep valleys and uneven slopes

52

Characteristics and processes associated with the development of Karoo

Landscapes

Mesa:

• A mesa is an isolated, flat-topped

hill or mountain with steep sides that

is smaller in area than a plateau.

53

Butte:

• A butte is also a flat-topped hill with steep sides, though

smaller in area than a mesa.

54

Horizontal Layers on Topographical Maps

The Concept of Scarp Retreat and Back Wasting Slopes eroding back parallel to their original position; common in dry climates where there is very little surface water

runoff; also known as back wasting.

Utilization of Horizontally Layered Landscapes Canyon landscapes are not attractive for settlement and agriculture. The wide valleys of these landscapes also make

the construction of infrastructure quite difficult.

The Karoo landscape is arid and not generally suited for agriculture or settlement. The area is, however, used

successfully for sheep farming.

55

Topography Associated with Inclined / Tilted Rock Strata

What is Inclined Rock Strata Asymmetrical ridge according to the

angle of a dip slope

Characteristics and processes associated with the development of Scarp and Dip

Slopes • It occurs when strata is subjected to stress

(either compression, tension, volcanic

intrusion or tectonic movement) and they

become tilted relative to their original

(horizontal) position.

• Faulting or folding causes the strata to be

tilted.

• The beds may be inclined in any direction

with the angle of the dip slope between 0º to

90º.

• Inclined strata has TWO slopes; a dip and

scarp slope.

Dip Slope Scarp Slope

A natural/gradual slope on the surface of the ground which is parallel to the dip of the underlying strata.

OR

A side on which hard layers dip and has a gentle slope.

It has a GENTLE SLOPE and a

RESISTANT ROCK LAYER.

A long steep slope or cliff at the edge of a ridge/ plateau.

It has a STEEP SLOPE and a SOFTER ROCK LAYER.

Characteristics and processes associated with the development of Cuesta,

Homoclinal Ridge and Hogsback Ridge • When the strata is weathered, asymmetrical ridges called homoclinal ridges are formed .

• Homoclinal ridges are where the underlying strata is tilted in the same direction and has a uniform dip angle.

(rock strata dipping in one direction).

• Homoclinal ridges are classified according to the angle of the dip slope.

• There are THREE types of homoclinal ridges, namely:

• cuesta

• homoclinal ridge and

• hogsback ridge

56

Cuesta

• A ridge with a gentle dip slope and a steep scarp

slope.

• The angle of the dip slope is 10º – 25º to the

horizontal.

• The dip slope does have fertile soil and is usually

used for forestry.

• Example: Magaliesberg Mountain in Gauteng

Cuesta Basins • Cuesta basins are formed as a

result of volcanic intrusions of a

lopolith.

• The scarp slope faces

downward, and the dip slope is

directed inward. These

hold artesian wells and can

form oil traps.

Cuesta Dome Cuesta domes are formed as a

result of volcanic intrusions of a

batholith and lacollith. The

scarp slope faces inward, and dip

slopes faces outward.

57

Homoclinal Ridge • The angle of the dip slope lies 25º – 45º to the horizontal.

• Rivers cut poorts through the ridges.

• Drainage is normally trellis patterned.

• Example: Magaliesberg near Pretoria and Hex River

Mountains in Western Cape.

Hogsback • The angle of the dip slope is more than 45º to the horizontal.

• There is very little difference in the gradient of the scarp and

dip slopes. Example: in Eastern Cape

Utilisation of Inclined Strata by Humans • Cuestas

1. are used for farming

2. are used for forestry

• Hogsbacks

1. For recreation – e.g. mountain climbing

2. For protection during war

58

Topography Associated with Massive Igneous Rocks

What are Massive Igneous Rocks?

Massive igneous rocks are not stratified. They

solidified at depth as a great compact mass and

cooling was therefore slow. Because of this slow

cooling process, there was sufficient time for

large crystals to develop. These large masses

can assume a variety of forms, namely,

batholiths, laccoliths, lopoliths, dykes and sills as

well as tors.

Batholiths The largest of the dome-shaped intrusive forms

is a batholiths. It reaches down to such great

depths, increasing in size deeper down, that it

seems to have no lower limit. Even the exposed part at the Earth’s surface often extends over several thousand

square kilometres.

Laccoliths The laccolith is much smaller than batholiths. It is also formed by the erosion of magma amongst other strata, e.g.

between sedimentary layers of rock. The overlying layers have to be removed before the laccoliths itself is visible.

Lopolith Lopoliths are formed in much the same way as laccoliths, but the sedimentary strata between which magma has

intruded have been unable to bear the weight. The floor has collapsed to form a shallow, saucer-shaped intrusive

form.

Dykes and Sills Dykes and sills can be the same material from the same source. Dykes find and fill vertical structural weaknesses. If

they find a weaker horizontal plane, they fill that too, forming a sill.

• A dyke is an intrusion into an opening cross-cutting fissure, shouldering aside other preexisting layers or

bodies of rock.

• A sill is a tabular sheet intrusion that has been intruded between older layers of sedimentary rock, beds of

volcanic lava.

Granite Domes

59

Tors

Question 1 Refer to the FIGURE showing topography associated with horizontally layered rocks. The 3 diagrams are not

arranged in the correct order of development.

1.1 Arrange the THREE diagrams in the correct order of development by writing the letters that

appear on the diagrams in the correct order. (3 x 2) (6)

1.2 The utilization of these types of landscapes, especially B, is limited. Explain the reason for

this. (1 x 2) (2)

1.3 Which one of the diagrams illustrates a typical Karoo landscape? (1 x 2) (2)

1.4 Identify the landform in the diagram mentioned in QUESTION 1.3 that is typically found in the

Karoo landscape. (1 x 2) (2) [12]

Question 2 Refer to the figure below, a photograph showing an example of inclined rock strata.

2.1 Explain how rocks are bent in this type of landscape. (1 x 2) (2)

2.2 Identify the type of Cuesta evident in the photograph. (1 x 2) (2)

2.3 Give a reason for your answer. (1 x 2) (2)

2.4 State the TWO types of slopes generally associated with inclined rocks. (4)

2.5 Draw a diagram to distinguish between these TWO types of slopes. (2x2) (4)

[14]

60

Question 3

Use the diagram to complete the table by matching the terms in column A with the definitions in column B.

Write only the number and the correct answer. (5 x 2) (10)

Column A Column B

3.1 Batholith A. A horizontal rock formed as magma spread between layers

3.2 Laccolith B. A wall like intrusion that cuts almost vertically across existing strata

3.3 Lopolith C. Magma intrudes between sedimentary layers. The layer underneath cannot support the weight and sinks downwards creating a saucer shaped intrusion.

3.4 Dyke D. A mushroom shaped intrusion that pushes the overlying strata upwards

3.5 Sill E. The largest of all intrusive forms.

Question 4 Refer to the figure below showing topography associated with massive igneous rocks.

4.1 What landform is evident in the picture above? (1 x 2) (2)

4.2 Describe the landform that you have identified in QUESTION 4.1. (1 x 2) (2)

4.3 Write a paragraph (approximately 8 lines) in which you explain the formation of the landform

identified in QUESTION 4.1. (4 x 2) (8)

[12]

Question 5 (Adapted from Gr 11 Exemplar, DBE, Paper 1, Question 1.2)

Refer to FIGURE 5 showing igneous intrusions and answer the questions that follow.

61

FIGURE 5: IGNEOUS LANDFORMS

5.1 Name the largest igneous intrusion labelled 3. (1 x 2) (2)

5.2 Label igneous intrusions 1, 2 and 7. (3 x 2) (6)

5.3 Which landform would develop if 1 is exposed to the Earth's

surface? (1 x 2) (2)

[10]

Question 6 (Adapted from Gr 11 Exemplar, DBE, Paper 1, Question 1.6)

Refer to FIGURE 6 showing cuestas and answer the questions that follow.

FIGURE 6: CUESTAS

6.1 What is a cuesta? (1 x 2) (2)

6.2 Describe the difference in the

formation of cuestas in diagrams A

and B. (2 x 2) (4)

6.3 Describe the difference between the

Dip slope and the scarp slope of a

Cuesta. (2 x 2) (4)

6.4 Discuss how humans can use

Cuestas. (2 x 2) (4)

[14]

Question 7 (Adapted from Gr 11 Exemplar, DBE,

Paper 1, Question 2.5)

Refer to FIGURE 7 showing two

landforms that develop in succession to

one another.

7.1 Identify landforms A and B. (2 x 2) (4)

7.2 Name the underlying igneous intrusion from which both these landforms developed. (1 x 2) (2)

7.3 Briefly explain why landform A assumes a rounded shape. (3 x 2) (6)

7.4 Write a short paragraph in which you explain how landform B develops. (6 x 2)(12)[24]

62

LESSON 6: GEOMORPHOLOGY II

SECTION A: SLOPES Key Concepts


• Overview of South Africa's topography

• Types of slopes

• Slope elements

• Characteristics of slope elements

• Slope development over time and the concept of slope retreat

Overview of South Africa’s Topography SA’s landscape has been shaped over a long time by movement below

the surface of the Earth and by the movement of water across the

surface of the Earth. Different layers of rocks have been laid down over

millions of years and then shaped by erosion. Different strata and rock

formations are eroded and the topography results from these

processes.

What is a Slope?

The angle which any part of the Earth’s surface makes with the horizontal

OR

Any geometric element of the Earth’s surface.

Types of Slopes

Gentle Slope A slope with contour lines spread far apart from each other. This even

spacing is maintained in both up and down slope.

Steep Slope A slope represented with contour lines close to each other on a

topographical map.

Convex Slope A slope which becomes progressively steeper downhill. It can refer to

an entire slope or part of one. On a map the contour lines will be

spaced closer together with a decline in height above sea-level.

63

Concave Slope A slope which becomes progressively steeper uphill. It

can refer to an entire slope or part of one. On a map

the Contour lines will be spaced closer with an

increase in height above sea-level.

Tectonic Slopes These are formed through internal forces that result in the folding, warping and faulting of rock masses or layers.

Anticlines and synclines, are formed when layers of rock are folded; while horsts (block mountains) and graben (rift

valleys) are formed when blocks of land rise or fall in relation to each other when faulting occurs.

Depositional Slopes Deposits of weather material build up to form inclined surfaces, mounds and hills when an agent of erosion (e.g. wind,

water or ice) which has lost its energy of motion, lays down its load in a particular place. Examples are alluvial fans,

alluvial cones, deltas and sand dunes.

64

Slope Elements

Crest

A small convex-shaped slope, with a

thin covering of soil

Freeface / Scarp Cliff

A near vertical slope, more than 80° to

the horizontal

Talus / Scree / Debris

A slope with a constant angle, and is

formed of eroded material from crest

and freeface

Knickpoint

The change in gradient at the base of the scree slope

Pediment

A low-angle concave slope

Characteristics of Slopes

Crest • Edge of the hill

• Convex

• Thin layer of soil

• Weathered material removed

Freeface / Scarp Cliff • > 80° to the horizon

• Layer hard resistant rock

• Loose material falls to bottom of cliff

• Cliff retreats parallel to itself

Talus / Scree / Debris • Accumulates from crest and cliff face

• Uniform slope

Pediment • Low angle, concave slope

• Slope is not uniform- steeper close to the talus slope

• Pediment increases as the slope increases backwards due to scarp recession

65

Slope Development over time and the Concept of Slope Retreat

SLOPE DECLINE (W.M DAVIS, 1899)

REGION OF STUDY Theory based on slopes in what was to Davis a normal climate (northwestern Europe and north-eastern USA)

CLIMATE Humid climate

DESCRIPTION OF

SLOPE

Steepest slopes at the beginning of the process with a progressively decreasing angle over time to give a convex upper slope and a concave lower slope

CHANGES OVER TIME

Assumed a rapid uplift of land with an immediate onset of denudation. The uplifted land would undergo a cycle of erosion where slopes were initially made steeper by vertical erosion by rivers but later became less steep (slope decline) until the land was almost flat (peneplain)

SLOPE REPLACEMENT (W. PENCK, 1924)

REGION OF STUDY Conclusions drawn from evidence of slopes in the Alps and Andes

CLIMATE Tectonic areas

DESCRIPTION OF

SLOPE

The maximum angle decreases as the gentler lower slopes erode back to replace the steeper ones giving a concave central part of to the slope

CHANGES OVER TIME

Assumed landscape started with a vertical rock slope with equal weathering overall. As scree (talus) collected at the foot of the cliff it gave a gentler slope which, as the scree grew, replaced the original one.

PARALLEL RETREAT (L.C KING, 1948, 1957)

REGION OF STUDY Based on slopes in South Africa

CLIMATE Semi-arid landscapes. Also sea cliffs with wave-cut platforms

DESCRIPTION OF

SLOPE

The maximum angle remains constant as do all slope facets apart from the lower one which increases in concavity

CHANGES OVER TIME

Assumed that slopes had two facets- a gently concave lower slope or pediment and a steeper upper slope (scarp). Weathering caused the parallel retreat of the scarp slope allowing the pediment to extend in size

Question 1 Refer to the FIGURE showing

elements of a slope to answer the

questions.

1.1 Identify the slope elements

labeled A, B, C, and D. (4x2)(8)

1.2 Describe slope element B.

(1 x 2) (2)

1.3 Identify at least ONE factor that

promotes fertile soil in area E

(1x2)(2)

[12]

66

SECTION B: MASS MOVEMENTS

Key Concepts

In this lesson we will focus on summarising what you need to know about:

• Concept of mass movements

• Causes of mass movements

• Kinds of mass movements

• The impact of mass movements on people and the environment

• Strategies to minimise the effects of mass movements

What is Mass Movement?

Mass movement is the down slope movement of earth materials under the

influence of gravity.

The detachment and movement of earth materials occurs if the stress imposed

is greater than the strength of the material to hold it in place.

Causes of Mass Movements Mass wasting is caused by gravity. On a mass of material gravity exerts a force downward proportional to the amount

of mass.

Because of the effect of water on slope stability, many mass wasting events are triggered or hastened by heavy or

extended rainfall.

Kinds of Mass Movements

Soil Creep

Creep is the slow, continuous movement of soil

or unconsolidated sediments over extended

periods of time.

Often, the rate of creep is less than a centimeter

per year and can only be detected over many

years by looking for its effect on the landscape

Causes of Soil Creep • Creep is caused by repeated freeze-

thaw cycles that slowly inch material

downslope (during freezing, particles are

elevated perpendicular to the slope, but

67

during thaws they fall straight down to a new position lower on the slope).

• Creep can also be caused by a buildup of pore water that allows material to begin to flow under the influence

of gravity.

Effects of Soil Creep • Creep causes fence posts, utility poles, walls, and other structures to lean over time. Eventually the lean

topples the structures and they must be rebuilt.

• In some cases, creep can be slowed or prevented by installing drainage pipes in soils that drain them and

keep pore pressures low.

Solifluction

• It is the down slope movement of soil over

a permanently frozen subsurface.

Solifluction is common on slopes

underlain by permafrost (permanently

frozen sub – soil).

• During the summer when the upper

permafrost is activated, the waterlogged

soil mass slowly moves down slope to

form solifluction lobes or terraces.

Landslides

A landslide is a movement of rock or debris

down a slope along one or more distinct

surfaces. Landslides range in speed from 1

m/day to as much as 300 km/hr.

Rockfalls

• Rockfall (free fall of rock) is an extremely rapid process and occurs without warning.

• Rockfall is typically the result of frost wedging.

• Frost wedging is a process where water enters cracks in

rocks, freezes, expands, and breaks the rock apart.

Mudflows

• Occur on moderate-to-steep slopes

• Movement is generally rapid

• Primarily fine-grained material (smaller than sand-sized

particles)

• May begin as shallow soil slip (shallow slides in soil over

rock that parallels the slope)

• Typically flows down slopes or follows drainage

channels

68

Slumps

• The sliding of material along a curved surface

called a rotational slide or slump.

• A common cause of slumping is erosion at the

base of a slope. For example, coastal storm waves

erode cliff bases, removing supporting material.

• The slump block rotates downward, producing a

scarp (cliff) at the top of the slope.

Effects of Mass Movement

69

Human Impact on Landslides Excavation into a slope (for a road or construction site) creates a flat area at the base of a slope.

However, it also over steepens the slope. Removing the basal support can result in slope failure.

Harvesting timber can also have an impact. Removing slope-supporting material (trees and brush), as well as

creating roads, affects the landscape. If the surficial (and sometimes subsurface) geology is unstable, mass wasting

often occurs.

Urbanization also has an effect on slope stability. Grading hillsides (cutting benches for building homes on) greatly

increases landslide potential.

Construction of homes on unstable slopes has similar effects. Changing the slope face, the additional weight

(homes and fill material), plus the added water (homeowners' sprinkler systems and septic tanks) make a formerly

stable slope unstable. Add a heavy rainy season and you have lots of landslides!

70

Strategies to Minimise the Effect of Mass Movements

Minimizing landslide hazards requires three steps:

1. Identification of landslide potential areas,

2. Prevention of landslides, and

3. Corrective measures when a landslide occurs.

Identification of Landslide Potential Areas

Identification is accomplished by

studying aerial photographs to determine sites of previous landslides or slope failures, and field

investigations of potentially unstable slopes.

Potential mass-wasting areas can be identified by steep slopes, bedding planes inclined toward valley floors,

hummocky topography (irregular, lumpy-looking surface) covered by younger trees, water seeps, and areas where

landslides have previously occurred. The information is then used to generate a hazard map depicting the various

landslide-prone areas. Prevention of Landslides

Controlling drainage and reducing the slope angle reduces landslide potential. Concrete interceptor drains can be

constructed to contain runoff and prevent infiltration. Steep slopes can be graded into gentler slopes. A series of

"stair-steps" can be created on very steep slopes.

Engineering methods can be used to help prevent slope failure. Retaining walls, rock bolts, and "shotcrete"

(coating of concrete-rock mixture on slope surface and crevices to prevent water entry) are used to inhibit slope

failure. Wire cables and wire fences minimize the danger of rockfall. Corrective Measures

Correction of some landslides is possible. This is accomplished by installing a drainage system, which reduces water

pressure in the slope, thereby preventing further movement.

The key to preventing damage from landslides is to identify and avoid developing landslide prone areas such as

steep, unstable hillsides. However, if some of these areas must be developed then building codes should require

extensive efforts to insure slope stabilization:

• vegetation of unstable slopes

• installation of drainage and runoff channeling structures

• benching and regrading of slopes to lessen their steepness

• stabilization structures such as retaining walls, deeply sunk pylons, and backfilled supports

Good slope engineering is expensive and the temptation to cut corners is great. However, landslide damage is far

more expensive and estimates have shown that for every rand spent on slope stabilization, between 10 and 2000

rand are saved over the long term.

Question 2 Refer to the FIGURE showing an element of mass

movement.

2.1 Identify the type of mass movement shown in the

diagram. (1 x 2) (2)

2.2 Describe how this type of mass movement occurs.

(2 x 2) (4)

2.4 Identify at least TWO impacts on human that this type

of mass movement would have. (2 x 2) (4)

[10]

71

Question 3


Read the article in FIGURE 1 and answer the questions that follow.

FIGURE 3: LANDSLIDES

The 2010 Uganda landslide occurred in the district of Bududa in eastern Uganda on 1 March 2010. The landslide was triggered by heavy rain between 12:00 and 19:00 that day. At least 100 people are believed to have been killed.

The landslide struck villages on the slopes of Mount Elgon, including

Nameti, Kubewo, and Nankobe. Eighty-five homes were destroyed in Nameti alone. Many areas in the affected villages were buried by the landslides, including houses, markets and a church. Many roads were also blocked. Officials and aid workers were worried that further landslides could occur, as heavy rain continued to fall in the region.

[Source: Wikipedia.org]

3.1 Define the term landslide. (1 x 2) (2)

3.2 Where do landslides generally occur? (1 x 2) (2)

3.3 State TWO causes of landslides. (2 x 2) (4)

3.4 Describe THREE impacts of landslides on people and the environment. (3 x 2) (6)

3.5 Write a short paragraph in which you explain strategies that can be used to prevent, or minimise, the effect of

mass movements. (6 x 2) (12)

[26]

Question 4


Refer to FIGURE 4 shows the typical slope elements/forms associated with a slope.

FIGURE 4: SLOPE ELEMENTS/FORMS

4.1 Identify the slope elements/forms

labelled A, B, C and D.

(4 x 2) (8)

4.2 Give ONE characteristic of each of

the slope elements/forms labelled A

and C. (2 x 2) (4)

4.3 Explain why slope element/form D is

useful to farmers. (2 x 2) (4)

[16]

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LESSON 7: EXAM QUESTIONS: CLIMATE & WEATHER

Question 1 Complete each of the following statements by choosing a word/term from the list below.

global air circulation; westerly winds; trade winds; geostrophic wind; Coriolis force; pressure gradient force

1.1. The ... causes air to be deflected from its original path. (1 x 2) (2)

1.2. Large-scale movement of air in the atmosphere is referred to as ... (1 x 2) (2)

1.3. The difference in air pressure causing air to move from an area of high pressure to an area of low

pressure is referred to as the ... (1 x 2) (2)

1.4 Winds that blows parallel to isobars in the upper atmosphere are ... (1 x 2) (2)

1.5 Winds that blow in the tropics are called ... (1 x 2) (2)

[10]

Question 2

Refer to FIGURE 2 showing igneous intrusions and answer the questions that follow.

2.1 Name the largest igneous intrusion labelled 3. (1 x 2) (2)

2.2 Label igneous intrusions 1, 2 and 7. (3 x 2) (6)

2.3 Which landform would develop if 1 is exposed to the Earth's surface? (1 x 2) (2)

Question 3 Refer to FIGURE 3 showing the West

African monsoon winds and answer the

questions that follow.

3.1 What is a monsoon wind? (1 x 2) (2)

3.2 Identify the wind which dominates

West Africa from January to March and

from June to September respectively.

(2 x 2) (4)

3.3 Describe the weather in West Africa

as a result of the wind that blows from

June to September. (2 x 2) (4)

3.4 State ONE problem associated with

the monsoon wind that blows from

January to March. (1 x 2) (2)

3.5 State ONE problem associated with the monsoon wind that blows from June to September. (1 x 2) (2)

[14]

10

73

Question 4 Refer to FIGURE 4 in order to answer the questions that follow.

Source: http://www.abc.net.au/science/slab/elnino/story.htm

4.1 What is the name given to the conditions illustrated in the diagram? (1×2) (2)

4.2 Explain why there is more warm ocean water on the west coast of South America. (2×2) (4)

4.3 Explain why Australia will probably experience below average rainfall. (2×2) (4)

4.4 What conditions is South Africa likely to experience during this time? (1×2) (2)

4.5 In a paragraph (between 10 and 15 lines), describe some of the effects that population on the east

coast of Australia might face as a result of the reduced rainfall and describe some strategies that

could be implemented to reduce the severity of these effects. (4×2) (8)

[20]

Question 5

Refer to FIGURE 5 showing cuestas and answer the questions that follow.

5.1 What is a cuesta? (1 x 2) (2)

5.2 Describe the difference in the formation of cuestas in diagrams A and B. (2 x 2) (4)

5.3 Describe the difference between the dip slope and the scarp slope of a cuesta. (2 x 2) (4)

5.4 Discuss how humans can use cuestas. (2 x 2) (4)[14]

http://www.abc.net.au/science/slab/elnino/story.htm

http://www.abc.net.au/science/slab/elnino/story.htm

74

Question 6 Read the extract from an article in FIGURE 6 and answer the questions that follow.

EAST AFRICA'S DROUGHT: THE AVOIDABLE DISASTER The deaths of tens of thousands of people during the drought in East Africa could have been avoided if the international community, donor governments and humanitarian agencies had responded earlier and more swiftly to clear warning signs that a disaster was in the making, according to a new report.

Figures compiled by the Department for International Development suggest that between 50 000 and 100 000 people, more than half of them children under five, died in the 2011 Horn of Africa crisis that affected Somalia, Ethiopia and Kenya. Hundreds of thousands remain at continuing risk of malnutrition.

The authors of the report, published by Save the Children and Oxfam, suggest current emergency response systems, which they believe to be seriously flawed, will soon be tested again as new humanitarian crises loom in West Africa and the Sahel, where growing food shortages are reported.

[Adapted from The Guardian, Wednesday 18 January 2012]

6.1 What does the term development aid refer to? (1 x 2) (2)

6.2 What is the difference between bilateral aid and humanitarian aid? (2 x 2) (4)

6.3 Name ONE humanitarian aid organisation that plays an important role in providing food to countries a

affected by famine. (1 x 2) (2)

6.4 Except food, name ONE other form of humanitarian aid. (1 x 2) (2)

6.5 Do you agree that humanitarian aid should be granted to avoid a humanitarian crisis in West Africa

and the Sahel? Motivate your answer by discussing the advantages and/or disadvantages of

providing humanitarian aid. (4 x 2) (8)

[18]

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