3.0: MAJOR FEATURES OF THE EARTH
Topic 3: MAJOR FEATURES OF THE EARTH’S SURFACE
Introduction
Earth is the third planet in arrangement and the fifth largest planet in the solar system.
Its surface is approximately 510 millions square kilometers. This means that earth is very large.
The surface of the earth is made up of two main features LAND and WATER BODIES
The land's surface area is estimated at 29% of the total area of the earth's surface, while water covers the remaining 71% of the total area of the earth surface.
Most of the land exists in large blocks called Continents. Likewise, most of the water is contained in large water bodies called seas and oceans.
CONTINENT
Continent is a major landmass rising from the ocean floor.
Formerly the continents were big landmass known as Pangaea. Due to the forces operating continuously, the landmass was separated into two parts namely Laurasia to the northern hemisphere and Gondwanaland to the Southern hemisphere.
Further separation or drifting led to the formation of the present continents which include Asia, Africa, North America, Southern America, Antarctica, Europe, Australia.
The boundaries of the continents with the exception of Asia and Europe were filled with water. Ural Mountains separated Europe and Asia. While other continents are separated by water bodies called seas and oceans. For instance African continent and Asia to the north are separated by Mediterranean sea and Red sea. Africa and South America are separated by Atlantic ocean, etc. The land surface occupies 29% of the surface of the earth, it forms seven continents. It includes Islands adjacent to the continents.
The seven continents are Asia, Africa, South America, North America, Australia, Europe and Antarctica. Oceans surround these continents. There is more land surfaces in the Northern Hemisphere than in the southern hemisphere.
The Size of continents and their Area (km2) are as follows
a. Asia (43 608 000 km2 ),
The continent is bordered to the north by the Arctic ocean, to the East by the Pacific ocean and to the south by the Indian ocean. Ural mountains form the boundary between Asia and Europe. The continent is attached to Africa by the Suez Isthmus which has bee dug to form Suez canal.
b. Africa (30 335 000 km2 ),
The continent is bordered to the north by the Mediterranean sea, to the East by the Indian ocean and to the west by the Atlantic ocean.
c. North America (25 349 000 km2 ),
The continent is bordered to the north by the Arctic ocean, to the East by the Atlantic ocean and to the west by the Pacific ocean.
d. South America (17 611 000 km2 ),
The continent is bordered to the East by the Atlantic ocean and to the west by the Pacific ocean and it is joined to North America by the Panama Isthmus
e. Antarctica (13 340 000 km2 )
This continent is situated in South pole and almost all of it lies within latitude 661/20 S. this continent is surrounded by the Southern Ocean.
f. Europe (10 498 000 km2 ) ,
The continent is bordered to the north by the Arctic ocean , to the west by the Atlantic ocean, east by Ural mountains and in south by the Mediterranean sea. It lies to the west of Asia separated by the Ural Mountains. g. Australia (7 682 000 km2).
The continent is bordered to the north and west by the Indian ocean, to the East by the Pacific ocean and to the South by the Southern ocean.
MAJOR RELIEF FEATURES OF CONTINENTS
The surface of any continent is not smooth. It has mountains, hills, plain and plateaus, river valleys, water bodies, basins and rift valleys. Altitude and slope give rise to the different relief features. Plain, plateaus and mountains form the major relief features of continent.
i) PLAINS
Plains are large and continuous stretches of comparatively flat land and not rising much above the sea level. Is undulating land usually near to the sea level or few hundred meters.
Many extensive plains are a result of down warping of the earth‘s crust for example, Siberia in Asia, North European plains, Indo- genic plain and the Great central plains of North America.
ii) PLATEAUS
Is the extensive high-altitude areas with more or less uniform summit levels.
They are formed when forces formed within the earth uplift a plain region. Major plateaus regions include the central plateau of Africa, the Brazilian Highlands and the Arabian plateau. The African plateau is higher in the South and East of the continent than it is in the north and west. In some areas, the outflow and spread of lava have formed plateaus over an extensive area, for instance the Deccan plateau in the India sub-continent and Colombia plateaus in the United states.
iii) MOUNTAIN
Is a large and elevated part of the earth‘s surface rising to greater height than ordinary hills. There are three major types of Mountains depending on how they are, These are;
a] Fold mountains
b] Block mountain
c] Volcanic mountain
d] Residual mountain
a] FOLD MOUNTAIN
The wrinkling of the earth‘s crust forms fold mountains, folding once occurs where rocks are laid in layers caused by compressional forces, fold mountains usually consist of high ranges that extend for hundreds of kilometers across the continent.
Thus fold mountains form the most extensive ranges in the world. For example the Rock mountains in North America vary in width from 640 to 1,600 kilometers and are about 5,000 kilometers in length. These types of mountains have some of the highest peaks of the world. Mountain Everest is 8,848 meters above sea level and the Andes is 7,003m above sea level. Apart from the Himalayas in Asia and the Andes in South America, this group of mountains includes the Andes-in South America, the Alps in Europe, the Atlas in North Africa, the Cap Rangers in South Africa, the Appalachians in U.S.A and the Great Divide Range in Australia.
b] BLOCK MOUNTAINS
Block Mountains(horst) are formed when a movement in the earth‘s crust forces the rocks to break. As a result, enormous cracks or faults are formed when sets of faults run parallel to each other and the ground between is forced up,
Usually Block Mountains do not extend over wide areas as Fold Mountains do. Example of block mountains are the Sambara, Uruguru and Ruwenzori mountains in East Africa, the Vosges and Black forest mountains in Europe and mount Sinai in Asia. Other features associated with faulting and Block Mountains are rift valleys or grabens.
c] VOLCANIC MOUNTAIN
TYPES OF VOLCANIC MOUNTAIN
* Active volcanic mountain; Are the volcanic mountains which still experience a periodic eruptions for example the mountain Italy, the Krakatoa in Indonesia, the Mufumbiro in Uganda, the Oldonyo Lengai in Tanzania and the Cameroons in Equatorial Africa.
* Dormant volcanic mountain; The volcanic mountains, which erupted only once in historical time and are no longer active, are said to be dormant. Good examples are the Kilimanjaro and Meru mountains both of which are in Tanzania.
* Extinct ( dead) volcanic mountain; Are the volcanic mountain which have not erupted for a very long time and have not shown any signs of erupting again. Good examples are the Kenya, Elgon and Rungwe Mountains, all of which are in East Africa.
Volcanic Mountains are usually conical in shape and mostly contain craters at their summits, for example, Fujiama and Kilimanjaro Mountains. Sometimes craters are filled with water to form crater lake for example, Lake Duluti and Ngorongoro both of which are in Arusha Region in Tanzania. Also Lake Ngozi found at Rungwe district in Mbeya.
d] Residual mountains
Apart from the three types of mountains, there are Residual Mountains which are formed by a prolonged denudation.
Denudation involves removing weaker rocks from the land the result of which landforms are lowered leaving behind resistant rock. The remaining resistant rock is known as residual mountains. Examples of residual mountains include the Haggard Mountains of central Sahara, the Sekenke hills of Singida in Tanzania, the Adamawa mountains of Eastern Niger, the Highlands of Scotland.
iv)RIFT VALLEYS
Rift valleys are formed when the land is between two sets of faults sink down.
The Great East African Rift valley is the longest in the world. It stretches from the Baka‘s valley east of the Lebanon mountains, through the Red sea, Ethiopia, East Africa to the lower Zambezi Area.
A branch of the valley runs along Lake Tanganyika in Tanzania to Lake Albert in Uganda.
The walls of a rift valley form fault lines or escarpments. Trenches formed by rift valley are sometimes filled with water to form Lakes like Lake Nyasa, Lake Albert, Lake Eyas, and Lake Turkana all of which are in East Africa and the Dead Sea in Jordan.
v)BASINS
A basin is a form of natural or artificial depression (hollow) varying in size in the earth ‘s surface.
vi)WATER BODIES
is any significant accumulation of water, Water bodies includes the following; rivers, oceans, lakes, dams, ponds, etc
a) RIVERS
is mass flow of water from highland (source) to lower land in a specific channel.
Tributaries; These are the streams that join together to form main streams or parent river
Distributaries; These are the small streams which are formed when the main river branches off before it enters the sea or lake.
Drainage basin, river basin or catchment area; Are the area from which the river system collect its rain water.
Water divide or water shed or basin perimeter Is the boundary between one drainage basin to the next.
River system (the water) divide enclosing a drainage basin
Water flows down a slope by the help of force of gravity, While flowing it carries minerals in solution, rock fragments and organic matters from high land area to low land area. The end of running water (run-off) is to the sea/ocean.
The main rivers in Africa
These are : The Congo River, The Niger river, The Orange river, The Nile river, The Zambezi river and the Limpopo river. The Congo, Niger and Orange rivers flows and pour their water into Atlantic Ocean. Zambezi and Limpopo flows into Indian Ocean. River Nile flows into Mediterranean Sea.
b) LAKES
Is a hollow in the earth's surface in which water collects. Lakes are formed when some run-offs(rivers) running and being holded by depressions or hollows on the continent. Example of Lakes is Nyasa, Victoria and Kyoga in Africa.
c) OCEANS
Ocean is a large body of salt water, that occupies about 75 percent of the earth‘s surface.
There is more water surface in the Southern hemisphere than in the North Hemisphere.
Features formed in water bodies
• Gulfs are the water inlets to the land. Example Persian Gulfs, Benguela, Guinea, and Mexico.
• Strait are the narrow water path separating one landmass from another. Example Gibraltar(morocco), Makasan(Indonesia), Luzon strait(Taiwan)
• Peninsula is the tract of land entering into a body of water. Example Msasani(Tanzania), Indian peninsula, Malaysia and Italy
• Cape is a piece of land jutting into the sea. Example cape of Good Hope(South Africa), cape verde, Guardafui, Palmas
Ocean include the Indian, the pacific, the Atlantic, the Arctic and the Southern Ocean. Ocean water contains a number of dissolved mineral salts. They include sodium Chloride (common salts) which makes up about 78 percent of all salt in the ocean water. Ocean water also contain compounds of magnesium, potassium, and calcium,
Sources of saltines in the ocean water
Ø Most of these minerals are in the ocean as a result of constant accumulation. Since the formation of the oceans
Ø Most minerals come from the land have been dissolved by water brought into the ocean by rivers, wind and ice.
Ø Another source has been volcanic activity that takes place in the oceans.
Saltiness of the ocean water is not the same everywhere in the ocean. Saltiness of ocean water depends mainly on
v Temperature which affects capacity of water to dissolve salt,
v the amount of fresh water brought into the ocean by rivers and rainfall and
v the amount of evaporation taking place from surface.
The table below shows the oceans and their size.
Sea is an expansive of salt water that sorrounded by landmass. Example of sea in the world include the Northern sea, Mediterranean sea, the China sea, the Red sea and the Dead sea
Movement of ocean water
Ocean water is constantly in motion. There are two types of movement .Which are Horizontal movement, which is in the form of current and tides.
Vertical movement which is the rising of sub- surface water and the sinking of surface water. those movement are:
(a)Ocean Current
An ocean current is the movement of surface water in the ocean.
These are warm and cold currents. Currents of the oceans are set in motion by prevailing winds; differences of density and temperature of the ocean water, the rotation of the earth and the shape of continent influence the flow of the major ocean current of the world.
(b)Tides
Tides are the rising and falling in the level of water in the ocean.
The tides occur twice in 24 hours. The level of which tides rise and fall varies slightly. On the days when it rises to its highest level it also falls to its lowest level. This rising and falling is caused by the pull of gravity of the moon and the sun.
(c) Waves
Waves are the up and down movement of the surface of water.
The highest part of the waves is called the crest and the lowest is called the trough. The distance from one crest to the next or from trough to trough called the wave length.
Upper waves travel in a definite direction, while the lower waves are the up and down movement. For example a cork thrown into the water does not travel with the waves. It moves up and down but not forward. Waves are driven to the shore by wind. The higher of the wave and the force with which it is driven are determined by the strength of the wind and the distance of open water which it has blown.
OCEAN FLOOR
The ocean floor ;Is the bottom of the surface of the ocean. The floor of the ocean is irregular. The diagram below shows the ocean floor. The major relief features of the ocean floor are;
A. The continental shelf
The continental shelf is a gently sloping margin of a continent. Continental shelf are occupied by shallow water that extends from the coast to the depth of about 200 meters towards the ocean basin. It provide an excellent condition for the growth of planktons.
B. The continental Slope
The continental slope is found at the point where the continental shelf forms a steep slope towards the ocean floor.
C. Oceanic Deep or Trenches
Ocean Deep or trenches are long narrow depressions or trough found on the ocean floor.
They plunge from the deep sea plain to depth of 10,000 meters or more example Marian trench, Atacama trench(coasts of Chile)
D. Deep sea plains or abyssal plain
Deep sea planes are the most extensive area of the ocean floor which is wide and gently undulating or fairly level surface which have depth between 2,000 meters to 3,000 meters. They are monotonous undulating areas. Large parts of these plains are covered with fine mud. E. The Ocean ridge
Ocean ridge is the raised part of the ocean floor. It takes the form of the ridge or plateau example the mid Atlantic ridge and Albatross plateau which rise above the water surface forms oceanic island.
F. Oceanic Island
Is the small land masses raised above the sea level that surrounded by water in all sides. Example Zanzibar island(pemba and Unguja), Ukerewe island.
