Thursday, 16 September 2021 11:16

The Physical Environment - Class 7 Social Studies Revision Notes

Position, Shape and Size of Africa

Position

Africa lies between latitude 37°N and 35°S and on longitute 18°W and 52°E.
Separated by water from all other continent except at the point where it joins Asia.
NOTE; When giving the position start with the latitude and then longitude.
Mostly Easterly point is called ras hafun(cape guardafui)
Mostly westerly is cape verde
Mostly northerly is cape bon
Mostly southerly is cape agulhas
Africa is connected to sinai peninsula by suez canal
Separated from spain by strait of gibraltar
Separated from rabia by strait of bab el-mandeb

Shape

The northern half is very wide while the southern is much narrower
At the cape guardafui extends outwards in the shape of a horn therefore the horn of africa.

Size

Africa is the second largest continent in the world
Has an area of about 30.3 million square kilometres(20% of the total land surface)
It measures 8000 km from north to south and 7400km from east to west
Other continents

  1. Asia – 43608000km2
  2. Africa – 30335000km2
  3. North america – 25349000km2
  4. South america – 17611000km2
  5. Antarctica – 13340000km2
  6. Europe – 10498000km2
  7. Australia – 8923000km2

Countries of Africa and their Location

Africa has the largest number of countries in the world making a total of 55 countries
The newest country is South Sudan
African countries are given below in alphabetical order:

Algeria                                              2381741km2
Angola                                             1246700km2
Benin                                               115773km2
Botswana                                         600372km2
Burkina faso                                     274200km2
Burundi                                             28490km2
Cameroon                                        475900km2
Cape verde                                      7275km2
Central africa republic                      622984km2
Chad                                               1284000km2
Comoros                                          2117km2
congo                                               34965km2
cόte d’ ivoire                                     322463km2
djibouti                                              23310km2
DR congo                                         2345409km2
Egypt                                                1101449km2
Equatorial guinea                             28051km2
Eritrea                                              124320km2
Ethiopia                                            1221900km2
Gabon                                              267667km2
Gambia                                            11369km2
Ghana                                              238537km2
Guinea                                             245957km2
Guinea bisau                                    36125km2
Kenya                                               582648km2
Lesotho                                            30460km2
Liberia                                              111369km2
Libya                                                 1775000km2
Madagascar                                      592900km2
Malawi                                              118484km2
Mali                                                   1240192km2
Mauritania                                         1030700km2
Mauritius                                            2040km2
Morocco                                            724730km2
Mozambique                                     802000km2
Niger                                                 1267000km2
Namibia                                             824295km2
Nigeria                                               923773km2
Rwanda                                             26338km2
Sόo Tome & principe                         964km2
Senegal                                            196192km2
Seychelles                                         453km2
Sierra leone                                       72325km2
Somalia                                             626541km2
South africa                                       221037km2
South sudan                                     644329km2
Sudan                                              1886068km2
Swaziland                                          17368km2
Tanzania                                            947419km2
Togo                                                   56785km2
Tunisia                                               164154km2
Uganda                                              236036km2
Western sahara                                 252120km2
Zambia                                              752618km2
Zimbabwe                                         390759km2
The largest country in africa is Algeria while the smallest is Sychelle.
Offshore island also form part of africa;

  1. Seychelle
  2. Sao Tome and principe
  3. Mauritius
  4. Comoros
  5. Madagascar
  6. Cape verde

Activity

Draw and label map of africa(including all countries)

Major Latitudes and Longitudes

Major longitude is called prime meridian also called greenwich meridian
In africa it passes through:

  1. Ghana(Accra)
  2. Algeria
  3. Burkina faso
  4. Mali

All other longitudes are measured and named from prime meridian upto 180° on both sides

Major latitude in are three passing through africa

  1. Equator 0°

    •  divides africa into two parts
    • It passes through;
      1. Gabon
      2. Congo
      3. DR congo
      4. Uganda
      5. Kenya
      6. Somalia
  2. Tropic of cancer 23½° north of equator

    It passes through;
    1. Western sahara
    2. Mali
    3. Mauritania
    4. Algeria
    5. Libya
    6. Egypt
  3. Tropic of capricorn 23½° south of equator

    It passes through:
    1. Namibia
    2. Botswana
    3. South africa
    4. Mozambique
    5. Madagascar

Other important lines of latitude are far from africa are:

  1.  Arctic circle 66½° N
  2. Antarctic circle 66½° S

Rotation of the Earth

This is movement of earth on its own axis. One complete rotation is 360°
The direction of the rotation is from west to east i.e.anticlockwise direction. One complete rotation takes 24 hours

Effects of Rotation of the Earth

  1. Differences in time along different longitudes
  2. Occurrence of day and night
    Effects on time note:
    24hrs=360
    1hr= ?
    (360 × 1) ÷ 24 =15
    Therefore 1hr=15 or 360 = (24×60)minutes=1440min
    1 = 1440 ÷ (360 ×1)= 4min

    Example 1
    The time in accra 0° is 7.00am.calculate time in bermbera 45°E
    1hr =15
    ? = 45 = (45×1) ÷ 15 =3hrs
    So 3hrs is equavalent to 45 then add 3hrs to 7.00am to get 10.00am

Revolution of the Earth

It is the movement of the earth around the sun on its own axis through a path known as orbit

Effects of the Revolution of the Earth

  1. Causes different seasons
    1. Summer
    2. Winter
    3. Spring
    4. Autumn
      The four seasons follows
      Summer → Autumn → Winter → Spring (SAWS)
  2. Differences in length of day and night
    • In December North pole experiences longer hours of darkness than days
    • In June south pole experiences longer hours of darkness than day
    • In March and September days and night are equal. This is because neither south pole or north pole is facing the sun or away from it.
  3. Position of the midday sun
    • On 21st June the sun is overhead at the tropic of cancer. This is called summer solstice
    • On December 22nd the sun is overhead at the tropic of capricon. This is called winter solstice.
    • On March 21st and September 23rd the sun is overhead at the equator. This is called Equinox.

Map Reading and Interpretation

A map is a representation of the earth or part of it on a flat surface.
The symbols used in a map help to identify;

  1. Economic activities
  2. Population distribution
  3. Relief
  4. Drainage of an area

Economic activities

These are things that people engage in to obtain wealthe.g –mining,fishing, farming, livestock keeping,trading,

 Quarry  People keep cattle or livestock
 Road  People and goods are transported using road
 Fish trap  People practise fishing
 National Park   Tourism activities are carried out

Relief

This is physical appreance of the earth’s surface. They include;

  1. Hills
  2. Valleys
  3. Plateaus
  4. Mountains
  5. Plains

High ground or plateaus may be identified by the presence of;

  1. Mountain
  2. River source
  3. Tea
  4. Coffee
  5. Pyrethrum

Low attitude or plains may be identified by presence of;

  1. Swamps
  2. Direction of flow of rivers
  3. Cotton

On the atlas colour:

  • Light green represent plains
  • Yellow represents plateaus
  • Brown represents highlands
  • Purple represents mountain tops

Drainage

Includes all water features. They are;

  1. Rivers
  2. Lakes
  3. Swamps
  4. Ponds
  5. Wells
  6. Human made lakes

Colour is used to represent drainage

  • Seasonal rivers – broken blue lines
  • Permanent rivers – continuous blue lines

Swampy areas have few settlement because they are breeding ground for mosquitoes

Population distribution and settlement

Many dots in an area indicate there are many people living there. Such areas are said to be densely populated.

When dots are far apart or scattered the area is said to be sparsely populated.

Physical Features

Main Physical Features of Africa

The main physical features in africa are:

  1. Plateaus
  2. Basins
  3. Valley
  4. Swamps
  5. Lakes
  6. Rivers
  7. Mountains and highlands

Activity
Our lives today pg 17
Draw map of africa showing main physical features

Plateaus

It is a high area which is generally level or flat ot the top

They are made up of very old and hard rocks

 Plateaus surface   Country where found
 Fouta Djallon  Guinea
 Bie plateau   Angola 
 Nyika plateau  East Africa
 Jos plateau  Nigeria

 

Basins

These are broad and shallow depressions. Most prominent ones are:

  1. Congo
  2. El Djouf
  3. Sudan
  4. Chad
  5. Kalahari
  6. Danakil depression

Other smaller basins – qattara in egypt,Lake victoria – kyoga basin

The lowest depression in africa is danakil depression

Valleys

It is a long depression on the earth surface
The world’s biggest and most famous is the great rift valley. It covers a distance of 5600km.

Great rift valley is divided into four sections

  1. Ethiopia rift valley
  2. Eastern branch
  3. Western branch
  4. Malawi rift valley

Ethiopian rift valley

  • It begins from the red sea and extends down to lake turkana

Eastern branch

  • Begins from lake turkana through kenya down to tanzania

Western branch

  • Starts from lake rukwa in tanzania and runs along the borders of uganda and DRC to south sudan border.lake tanganyika, kivu,goerge,albert and edward are found in this branch.

Malawi rift valley

  • It is a continuation of the eastern branch. Starts from lake malawi and ends at port of beira in mozambique
    River shire valley, luangwa of zambia and the urema trough of mozambique are found here

Mountains and Highlands

The main highlands in africa include:

  1. Ethiopian highlands 
  2. Guinea highlands
  3. Adamawa highlands in cameroon.
 Mountain    Country where found 
 Kilimanjaro   Tanzania 
 Kenya  Kenya 
 Elgon  Kenya/Uganda 
 Cameroon  Cameroon 
 Gimbala  Sudan 
 Ras dashan  Ethiopia 
 Margherita  Uganda/Congo 
 Toubkal  Morocco

 

 Mountain Range    Country where found 
 Atlas  Morocco 
 Drankensberg  South Africa, Lesotho, Swaziland  
 Usambara  Tanzania 
 Cape Ranges  South Africa 
 Ruwenzori  Uganda 
 Ahaggar  Algeria 
 Tibesti  Chad 
 Aberdare  Kenya

 

Lakes

Natural lakes

Lake victoria, tanganyika, malawi, chad, bangweulu.

  • Victoria is the second largest lake in the world
  • Tanganyika is the deepest (second)lake in the world

Human made lakes

Volta – ghana, kainji – nigeria, nasser – egypt, kariba on border of zambia and zimbabwe.

Some lakes are salty e.g. magadi, natron, shala, bogoria, nakuru.

Salty lakes have no river flowing out of them.

Rivers

Major rivers include the:nile, congo, niger, zambezi, benue, orange, limpopo, volta, senegal,

River Nile is the longest in africa

Rivers that form delta are; Niger, and Nile

Niger delta is the largest in africa

Other rivers drain into the sea or lake in a single channel called estuary.
Examples: are zambezi, congo and senegal.

Swamps

They are areas of soft,wet land covered with vegetation.

They are named according to the types of vegetation in them e.g.papyrus swamps have papyrus reeds

Mangrove swamps have mangrove trees.

Examples of swamps are;

  • Okavango and makarikari in botswana
  • Sudd along the nile in south sudan
  • Lorian in kenya
  • Lake – kyoga in uganda
  • Malagasi in tanzania
  • Swamp around lake chad

Formation of Mountains

There are four types of mountains

  1. Block mountain
  2. Volcanic mountain
  3. Fold mountains
  4. Residual mountains

Fold mountains

Formed after sedimentary rock fold at the edges

Examples of fold mountains includes:

  • atlas in north africa
  • Cape ranges in south africa
  • Drankenberg in south africa

Residual mountains

Formed when rock masses are reduced in size after many years of erosion

Examples are namuli – mozambique, homboli – mali

Other smaller features which may be formed in smaller manner are inselbergs

Formation of Lakes

A lake is hollow or depression on the surface of the earth which is filled with water. Lakes are formed in different ways

  1. Erosion
  2. Earth movements
  3. Deposition
  4. Volcanic actions
  5. Human activities

Erosion

May be either through action of wind or glaciers

Wind actions
Examples are maghra, birket(lake siwa)both in egypt

Glacier actions
A glacier is a big block of moving ice

It is found on top of high mountains

Glacial lakes are known as tarns or corrie lake. Examples are teleki, hanging, gallary

Materials eroded by ice(moraine)may be deposited to form a barrier in a valley.

Behind such a barrier water may be collected to form a moraine dammbed lake.

Earth movements

They are of two types.these are;faulting and downwarping

  1. Faulting
    Examples are:
    • Lake tanganyika – tanzania
    • Eyasi – tanzania
    • Malawi – malawi
    • Edwajrd and george – uganda
    • Turkana, baringo and magadi – kenya
  2. Downwarping
    Examples of downwarping lakes are:
    • Victoria
    • Kyoga
    • Bangweulu
    • Chad

Deposition

The lakes formed in this manner are ox-bow lakes
Examples are:

  • Utange – on river rufiji in tanzania
  • Kanyaboli – on river yala in kenya
  • Gambi – on river tana in kenya.

Such lakes can also form in a delta areas e.g. lake manzala on nile delta.

Activity
draw diagrams on our lives today pg 24.

Volcanic activity

  1. Crater lakes
    Examples of crater lakes are:
    • Lake shala – ethiopia
    • Lake nyos – cameroon
    • Lake paradise – kenya
  2. Lava – dammed lakes
    Formed when water accumulates behind the lava barrier to form a lake
    Examples:
    • Lake kivu – uganda
    • Lake tana – etiopia
    • Lake itasy – madagascar
    • Lake bunyoyi – uganda

Human activities

Lakes formed as a result of human activities are called artificial lakes
Examples:

  • Lake nasser
  • Lake kariba
  • Lake volta

Relief Regions of Africa

Relief regions in africa are

  1. Plateaus
  2. Rift valley
  3. Highlands and mountains
  4. Coastal and lowlands

Plateaus

Is high and generally level ground
They lie between 400 – 2600 m above sea level
They have residuals hills (inselbergs)and valleys\
They are separated by short steep slopes known as scarps or escarpments.

The rift valley

The great rift valley enters africa from the red sea to beira in mozambique.
The narrowest part is about 30km wide while the widest is about 100km.
There are depressions occupied by lakes; e.g. bogoria and malawi etc
There are hills and mountains e.g. mt.longonot, suswa and ruwenzori
Some rivers flow along the floor of the rift valley .e.g. kerio, ewaso nyiro, and semliki

Highlands and mountains

Areas lying above 2000m can be described as highlands
Areas lying aove 2600m form mountains
The main highlands and mountains in africa

  1. Atlas mountains – morocco
  2. Ethiopia highlands – ethiopia
  3. East african highlands
  4. Ahaggar and tibesti mountains – chad
  5. Adamawa highlands – cameroon.
  6. Drankens berg and cape ranges – south africa
  7. Guinea highland – guinea

Mt.kilimanjaro is the highest in africa 5895m
Mt kenya – 5199m
Mt ruwenzori – 5109m

Coastal plains and lowlands

These are low – lying areas that border coast
They lie 0 – 400m above sea level.
They are narrow
Many parts are covered by sandy beaches

Climate

Climate is the average weather conditions of a particular place over a long period of time normally 30-35years

Factors Affecting Climate

  1. Relief and altitude
  2. Wind
  3. Latitudes
  4. Ocean currents
  5. Shape of the coastline
  6. Distance from the sea

Relief and Altitude

It influences the temperatures, the higher you go the cooler it becomes. The rate for every 100m of vertical height is 0.6
It also affects rainfall

Winds

Onshore wind absorbs water vapour from the sea and therefore bring rain to the land.
Offshore wind are dry winds and bring no rainfall.
The wind which influenceclimate in africa are;

  1. Westerly winds – bring rainfall to mediterranean
  2. North-east trade winds – they are offshore wind since they originate from asia.
  3. South-easttrade winds – they bring alot of rainfall to eastern africa
  4. South-westerly winds – they bring alot of rain to west africa and congo basin.
  5. Hamarttan winds – they are hot and dry. They cause dry conditions to the north and west africa.

Activity
Draw map of africa showing the winds.our lives today bk 7 pg 29

Latitude

This is the distance from equator.
Places near the equator experiences high temperatures while those far awy expriences lower temperatures
Africa lies within the tropics that is 23½° N and 23½° S. This region does not experience big change in
temperature during the different seasons.
Places outside the tropics experience winter and summer seasons. This is because the farther away one moves
from the tropics the cooler it gets.

Ocean Currents

These are the horizontal movements of water in the ocean.
They can be either be cold or warm.
Cold moves toward the equator while warm away from the equator.
The cold ocean currents are;

  1. Canary current
  2. Benguela current
    Cold current cause fog and mist to land

Warm currents are;

  1. Somali current
  2. Mozambique current
  3. Guinea current
    Warm currents causes rainfall to the land

Distance from the sea

Places that are far away from the sea receive low rainfall than those that are near.
This rainfall is called convectional rainfall
The sea also helps in the formation of cool sea breezes and land breezes

Shape of the coast line

When winds blow parallel to the coastline, they bring no rainfall to the land e.g. coast of ghana
Example axim town receives more rainfall than accra.

Climatic Regions of Africa

Africa has the following climatic regions

  1. Equatorial
  2. Tropical/savannah
  3. Mediterranean
  4. Mountain
  5. Desert and semi desert
  6. Humid sbtropical
  7. Warm continental

Characteristics of climatic regions of africa

Equatorial Climate

Also called hot and wet climate It is experienced in;

  • Nigeria
  • Liberia
  • Cote d ivoire
  • Sierra leone
  • Gabon
  • Cameroon
  • Congo
  • Democratic repblic of congo

Characteristics

  • Receives heavy rainfall – highest rainfall between April to June and lowest rainfall between september to october
  • Have double maxima rainfall
  • Most of the rainfall is convectional
  • Rainfall is accompanied by thunder and lightning
  • Temperatures are high throughout the year
  • No dry season
  • Dinurnal temperature range is small
  • High humidity

Savannah Climate

Also called tropical climate. 
Mainly found within the tropics

Characteristics

  • Experiences hot rainy season and acool dry season
  • Temperature range is between 15 C to 25 C.
  • When the rainy season is being experienced in the north of the equator, the dry season inthe south of africa and vice versa
  • Rainfall ranges from 380mm to 2000mm p.a.

Mediterranean Climate

It is experienced to the north africa along coast of;morocco, algeria, tunisia and around benghazi in libya.
Also experienced in south africa around cape town.

Characteristics

  • Experience hot, dry summer and cool, wet winter
  • During the winter season, winds are on shore hence rain , while during summer winds are offshore hence no rain.
  • Annual rainfall varies from 500 – 750mm
  • Most rainfall is brought by westerly winds
  • Temperatures range between 13 C and 24 C.

Semi – desert Climate

Experienced in kalahari and the sahal regions
This region have low rainfall and high temperatures

Characteristics

  • Rainfall between 380-500mm p.a.
  • Temperature between 22 C to 27 C
  • The skies are generally clear

Desert or Arid Climate

True desert are experienced in sahara in north africca and in the namib in namibia

Characteristics

  • Lands are dry
  • Highest temperatures 58°C and lowest 4°C
  • The skies are normally cloudless
  • Diurnal
  • Temperature range is very big.
  • Rainfall is less than 250mm p.a. it fall within short period accompanied by storms.

Humid Subtropical Climate

Experienced in the coastal areas of eastern cape province and natal in south africa and also in mozambique.
Is influenced by warm mozambique currents and south east trade wind.

Characteristics

  • Rainfall between 900 to 11500mm
  • Most rainfall falls in summer.
  • Both convectional and relief rainfall are recieved.
  • Temperature range betwwen 13°C to 26°C.

Warm Continental Climate

Also known as the high veld climate
Experienced between the mediterranean climate zone of cape region in south africa and the humid subtropical
zone.

Characteristics

  • Rainfall received all year
  • Annual rainfall between 780mm in the east and 400mm in the west
  • Winds from the indian ocean influence the rainfall.
  • Temperature from 10°C to 19°C.

Mountain Climate

Also known as alpine climate
It is influenced by altitude

Characteristics

  • Temperature decreases with increase in altitude
  • High rainfall is received in mountain areas due to rising of moist air.
  • Seasons exprienced in africa

Activity draw the diagrams on our lives today bk 7 pg 37

Places outside the equatorial regions but within the tropics, we have tropical region.these regions experience dry seasons and rainy seasons during other parts of the year.

Places farther away from equatorial and tropical regions experiences the four seasons

Mediterranean lands experiences hot and dry summer and cool, wet winter

Arid and semi-arid regions experiences hot and dry seasons throughout the year.

Influences of Climate on Human Activities

  1. Savannah are used for grazing
  2. Wild animals in savannah encourage tourism
  3. In the hunid subtropical region of south africa sheep are reared for meat and wool.
  4. Sawmilling is common in equaltorial regions
  5. Nomadic pastralism is practised in desert and semi desert regions
  6. Farming is practised in equatorial, modified equatorial, tropical and subtropical climatic zone.
  7. Tourism is practised at the top of mt.kenya, kilimanjaro and ruwenzori mountain because of snow.
  8. Climate influences types of houses to be built e.g.in wet areas the roof is steep for water to drain while flat tops are built in hot areas e.g. manyatta among the maasai.
  9. Areas that encourages breeding of mosquitoes and tsetse discourage settlement e.g.miombo woodland in tanzania and lambwe valley in kenya

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Read 2202 times Last modified on Monday, 20 September 2021 09:02