MAJOR FEATURES OF THE EARTH’S SURFACE
What is the earth?
Earth: is the third planet in the solar system which support life of plants and animals. Therefore the earth is the fifth largest planet in the solar system. Its surface is approximately about 510 millions square kilometers. This means that earth is very large.
CHARACTERISTICS OF THE EARTH
1. Is the fifth largest planet in the solar system.
2. It is only planent in the solar system which belived to have ability to support life.
3. It is not more hoter or more cooler.
4. It has the spherical shape, the earth is flattened at the poles but also it is wide at Equator.
5. About 75% of the earth is covered by water and only only 25% covered by landmass.
6. The large part of the southern hemisphere is covered by Water masses like ice and ocean while the large part of northern hemisphere is covered by Landmasses.
The surface of the earth is made up of two main features LAND and WATER BODIES the land's surface area is estimated at 29.2% of the total area of the earth's surface, while water covers the remaining 70.8%. 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. Normally the formation of continents it can be traced back by theory called Continental Drift Theory.
The theory was first developed by Fransis Bacon in 1620 but later it was advanced by Alfred Wagner in 1912. The theory state that "About 250 million years ago the present continents were single landmass called Pangaea. This landmass was sarounded by ocean called Panthalassa.
About 200 million years ago due to the various forces operating continuously the landmass was separated into two parts namely Eurasia to the northern hemisphere and Gondwanaland to the Southern hemisphere, hence these two landmass were separated by narrow sea called Tethys.
About 150 million years ago due to continuous forces the two landmass were futher divided and leads to the formation of the present continents which include, Eurasia produced, North America, Europe, and Asia. While Gondwanaland produced, S. America, Africa, Antarctica and Australia.
EVIDENCES OF THE THEORY
The continental drift theory is supported by the following evidences:-
1. The Jig-fit: this evedence based on looking the possibility of one continent to fit in one another. E.g Australia with Asia, S. America with Africa, N. America with Europe, etc
2. Biological evidences: the study of animal and plant. There are similar plant and animal species at the different continets.
3. Geological evidence: the studybof rocks proved that the rocks found from the different continent give the similar age, structure and composition.
4. Climatic evidence: the theory claimed that the present of snow in Australia it originated from the antactica when the continents were united.
5. Geomorphological evidences: it based on the study of mountains found in different continents. E.g Atlas mountain in N. Africa and Alps mountain in S. Europe give the same age, structure and directions.
6. Formation of riftvalleys: riftivalleys indifferent partparts of the world proves that the continental drift took place e.g Riftivalley in E. Africa.
CONTINENTS, SIZE AND LOCATION
1. Asia: is he first larges continent in the world. It located to the east of the Ural mountain and Suez canal and South of Caspian sea it cover abou 43,608,000 square kilometers.
2. Africa: Is the second largest continent in the world. It Located in the Southern hemisphere bordered by Red sea and Suez canal to the north east, mediterranean sea to the north Atlantic ocean to the west and Indian ocean to the South East. It cover about 30,335,000 square kilometers. Is the continent enclosed by tropic of Capricorn.
3. North America: It located in the Northern hemisphere surrounded by oceans, to the north Atlantic ocean, to the east Arctic ocean to the west Pacific ocean. It cover about 25,349,000 square kilometers.
4. South America: It is located to the Southern hemisphere and small part of the continent is located in the northern hemisphere. It is separated with Atlantic ocean to the north and North east, to the west Pacific ocean to the south southern sea. It cover about 17,611,000 square kilometers.
5. Antarctica: It is Located in the Antarctic region in the Southern hemisphere. Antarctica is surrounded by the Southern ocean. Almost 98% is covered by ice. It cover about 13,340,000 square kilometers.
6. Europe: Is continent located in the northern hemisphere. The continent is surrounded by, Black sea (South east), Arctic ocean (North), Atlantic ocean (West) and Mediterranean sea (South). It cover about 10,498,000 square kilometers.
7. Australia: Is the continent located in the Southern hemisphere near New zealand. The continent of Australia along with zealand constitutes a region called oceania or Australasia. It cover about 7,682,000 square kilometers.
THE MAJOR FEATURES OF THE CONTINENT
Continent is a major landmass rising from the ocean floor. Normally the earth has two major parts which are:-
1. Northern hemisphere: the large part of the northern hemisphere is covered by land mass.
2. Southern hemisphre: large part of the southern hemisphere is coverd by water masses such as ocean and ice. Therefore the continent consists of the following features:-
1. PLAINS
Plains: are continuous flat land and not rising much above the sea level. Many extensive plains are the result of down warping of the earth’s crust.
Example of plains
i. Siberia in Asia.
ii. North European plains.
iii. Indo- getic plain.
iv. The Great central plains of North America.
Sometimes the depression caused by down warping are filled with water to form down warping lakes like Lake Victoria in Tanzania.
2. RIFT VALLEYS
Rift valleys: are elongated troughs or depressions on the earth surface which produced by faulting of the earth crust. Normally riftvalley, is an elongated trough bounded by in facing fault scarps along more or less parallel faults.
Example of rift valleys
i. The Great East African Rift valley, is the longest rift valley in the world. It stretches from the Baka’s valley east of the Lebanon mountains (middle east) 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.
ii. Middle Rhine Rift valley which run between the Vosges and black forest mountains in Europe.
Trenches (depressions) formed by rift valley are sometimes filled with water to form rift valley Lakes like, Lake Tanganyika, Lake Nyasa and Lake Eyas in Tanzania, Lake Albert, Lake Natron in Uganda, and Lake Turkana in Kenya, all of these are found in East Africa and the Dead Sea in Jordan.
Types rift valley
i. Rift valley by tension
ii. Rift valley by compression
iii. Plate tectonics
3. PLATEAUS
Plateau: is the steep sided highland area with fair flat surface at the tope. They are formed whn forces formed within the earth uplift.
Example of plateaus
i. The central plateau of Africa.
ii. The Brazilian Highlands.
iii. The Arabian plateau.
4. MOUNTAINS
Mountain: is the highland area on the earth sufaces wchich has more than 1000m altitude above the sea level.
Major types of mountains
There are four major types of Mountains which are:-
i. Fold mountains.
ii. Block mountain.
iii. Volcanic mountain.
iv. Residual mountains.
A. FOLD MOUNTAINS
Fold mountains: Are the mountains which produced by folding of the earth crust. The folding are caused by compressional forces.
Compressional forces: Are those forces which cause materials to move towards each other.
For example of fold mountains
i. The Rock mountains in North America which has width of about 640 to 1,600 kilometers and about 5,000 kilometers in length.
ii. Mount Everest in Asia: which has about 8,848 meters above sea level.
iii. Mount Andes in South America which has about 7,003m above the sea level.
iv. Himalaya mountain in Asia.
v. The Alps mountain in Europe.
vii. The Atlas mountain in North Africa (Morocco).
viii. The Cape Ranges in South Africa.
ix. The Appalachians in U.S.A.
x. The Great Divide Range in Australia.
NB: The highest mountain in the world is mount Everest in Asia.
B. THE BLOCK/HORST MOUNTAINS
Block Mountains: Are the mountains formed by faulting of the earth crustal rocks. Normally block mountains are formed when sets of faults run parallel to each other and the ground between is forced up or to rise above. The block mountains (horst) are formed by faulting.
Faulting: Is the process which involves the formation of fractures or cracks in the rocks associated with rocks displacement.
Faults: Is the cracks or fractures in the rocks caused by rocks displacement as the result of tensional forces and compressional forces.
Tensional forces: Are forces which cause materials to move a way from each other.
Example of Block mountains
i. Mount Usambara in Tanzania.
ii. Mount Uruguru in Tanzania.
iii. Mount Ruwenzori in Uganda.
iv. Black forest mountains in Europe.
v. Mount Sinai in Asia, (Middle east).
C. VOLCANIC MOUNTAINS
Volcanic mountains: Are mountains that are formed by volacanic eruptions. They are formed when the large masses of lava accumulated and form the mountain. Normally volcanic Mountains are usually conical in shape and mostly contain craters at their summits.
For example of volcanic mountains
i. Fujiama mountain.
ii. Kilimanjaro Mountains.
iii. Mount Meru.
iv. Mount Italy.
v. The Krakatoa in Indonesia.
vi. The Mufumbiro in Uganda.
vii. The Oldonyo Lengai in Tanzania.
viii. The Mount Cameroon in west Africa.
Sometimes craters/caldera may filled with water to form a lake called Ccrater or Caldera lake. For example
i. Lake Duluti.
ii. Ngorongoro craters in Arusha Region in Tanzania.
iii. Lake Ngozi found at Rungwe district in Mbeya.
TYPES OF VOLCANIC MOUNTAINS
i. Active volcanic mountain: These are volcanic mountains with volcanoes which still experiencing the periodic eruptions. Example: Muntain Italy, the Krakatoa in Indonesia, the Mufumbiro in Uganda, the Oldonyo Lengai in Tanzania and the Cameroons in Equatorial Africa.
ii. Dormant volcanic mountains: These are volcanic mountains with volcanoes which erupted only once in historical time but they shows signs of eruption again. Example Kilimanjaro and Meru mountains in Tanzania.
iii. Extinct ( dead) volcanic mountain: Are volcanic mountains with volcanoes which as stoped eruption for a very long period of time and has no any signs of eruption again. Examples: Mount, Elgon and Rungwe, in Kenya, East Africa.
VOLCANOES
Volcano: Is a mould or a cone like features or a circular in shape build up through volcanic activity (is a result from volcanic activities)
TYPES/CLASSIFICATION OF VOLCANOES
i. Active Volcano.
ii. Domant Volcano.
iii. Extint Volcano
1. Active volcano: is the volcano which erupts frequently. Example Oldonyo Lengai in Tanzania and Mount Cameroon.
2. Dormant volcano: is the one which has stopped erupting but not extinct and it is expected to erupt. The dormant volcano is also known as sleep volcano. Example mount Kilimanjaro in Tanzania.
3. Extinct volcano: is the volcano which has stopped erupting for a very long time in history and is not expected to erupt. It is also known as dead volcano. Example mount Meru in Tanzania.
D). RESIDUAL MOUNTAINS
Residual mountains: Are mountains procuded by denudation as result of erosion caused by running water, wind or ice.
Denudation: is the process of removing of weaker rocks from the land by using erosional agents like running water, ice and winds.
Examples of residual mountains
i. The Haggard Mountains in central Sahara.
ii. The Sekenke hills of Singida in Tanzania.
iii. The Adamawa mountains in eastern Niger.
iv. The Highlands of Scotland.
v. The sierras of central Spain.
vi. The Mesa and Butte of the western plateau in USA.
5. BASINS AND DRAINAGE OF THE CONTINENT
A basin: Is the natural or artificial wide depression on the earth surface. Basins are produced by faulting as the result of both tensional and compressional forces.
Drainage: Is the removal of water from the land.
The over land flow: Is the flow of rain water on the ground surface. Underground flow: Is the process where by rain water sinks into the ground. Run- off: Is the flow of rain water over the ground and under the ground.
6. RIVERS
River: is the channel whereby Water flows from highland to low land by the force of gravity. When the rain falls or snows melt, water flows in small channels which finally join together and form large streams or RIVERS.
SOURCES OF RIVERS
The river sources/courcee: is the channel or point where the river originate or starts. Normally sources of rivers are,
i. Heavly rain.
ii. Melting of ice.
iii. Lake.
iv. Swamps or Marshes.
v. Springs.
RIVER MOUTH
The river mouth: is the place or point where the river pour its water. Normally the river mouth may be, lake, ocean or swamps. The river mouth: is the ending of running water which can be either ocean or sea.
Tributaries: These are small streams that joining together to form the main river. Distributaries: These are the small streams which are formed when the main river divided in to several branches before enters to the sea or lake.
River basin/Catchment area: Is the area where the river system collect its rain water. Water divide/Water shed/ Basin perimeter: Is the boundary between one drainage basin and next.
MAIN TYPES OF RIVERS
1. Parrenial rivers: are those rivers that flow throughout the year.
2. Intermittent rivers: are those rivers that flow only during the rain season, but the rivers experience dryafter the rainy season stopped.
3. Ephemeral rivers: these are rivers that flow only during the rain seasons in dessert areas. However these river experience drying up remediately after the rain season stopped.
THE MAIN RIVERS IN AFRICA
1. The Nile river: it flow and pour its water in to the Mediterranean sea.
2. The Niger river: it flow and pour its water in to the Antlantic ocean.
3. Congo River: it flow and pour its water in to the Antlantic ocean.
4. The Orange river: it flow and pour its water in to the Antlantic ocean.
5. Zambezi river: It flow and pour its water in to the Indian ocean.
MAIN RIVERS IN TANZANIA
i. River Rufiji.
ii. River Ruaha.
iii. River Pangani.
iv. River Malagalasi.
v. River Ruvuma
vi. River Wami.
vii. Umba river.
viii. River Zig.
THE VOLUME OF WATER IN THE RIVERS (RIVER REGIME)
The water volume in the river it is not uniform throughout the river, it varies seasonally. During the rainy season or when ice melts, streams channels carry more water than in dry season.
FACTORS AFFECTING WATER VOLUME IN THE RIVER
i. Climate.
ii. Slope.
iii. Vegetation.
iv. The nature of rocks.
v. Human activities.
vi. The length of the river.
7. LAKES
Lake: Is a hollow or depression on the earth surface where water accumulates. Lakes are formed when some run-offs (running and being holded by depressions or hollows on the continent) have their outlets to the sea.
TYPES OF LAKES
1. Lakes produced by tectonic movement: this include:-
i. lakes due to rift valleys e.g lake Tanganyika, Nyasa, etc.
ii. Lakes due down warping E.g lake Victoria.
2. Lakes produced by volcanic activities. This include:-
I. Carter and caldera lakes. E.g Lake Ngozi in Tanzania.
ii. Lava famed lakes.
3. Lakes produced by erosion. This include:-
I. Lakes due to glacial erosion. E.g Trough lakes, cirque lakes, rhibon lakes, rock basin lakes.
ii. Lakes due to wind erosion. E.g oases lakes.
iii. Lakes due to water erosion. E.g pluge lakes.
iv. Lakesdue to karst erosion.
4. Lakes produced by deposition: this include:-
I. Lakes due to water deposition. E.g delta lakes, ox-bow lakes, etc.
ii. Lakes due wave erosion e.g solution lakes.
5. Lakes produced by Mass wasting. E.g Barrier lakes.
6. Man made lakes. E.g Kariba dam, Aswan dam, etc.
MAIN LAKES IN EAST AFRICA
i. Lake Victoria.
ii. Lake Nyasa.
iii. Lake Tanganyika.
iv. Lake Kyoga.
v. Lake Truknana.
vi. Lake Natron.
8. 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.
MAJOR OCEANS OF THE WORLD
1. The pacific Ocean: is the first largest ocean in the which cover about 168.7 million kilometer squares.
2. The Atlantic ocean: Is the second largest ocean which cover about 85.1 million kilometer squares.
3. The Indian Ocean: is the third largest ocean which cover about 70.5 million kilometers kilometer squares.
4. The southern ocean: It is the fourth largest ocean in the world which cover about 22.0 million kilometer squares.
5. The artic ocean: Is the lowest and the last largest ocean in the world which cover
about 15.6 million kilometer squares.
Major types of sea in the world.
1. Mediterranean sea.
2. Red sea.
3. The southern China sea
4. The Caribbean sea
THE OCEAN SALINITY
Ocean salinity: Refers to the amount of salt content in the ocean water. concentration.
Salinity: is the measure of salt dissolved in the water body. Normally Salt content in the oceans comes from rock minerals, rainwater contains dissolved carbon dioxide from the atmosphere, making it slightly acidic due to carbonic acid that is formed from carbon dioxide and water. This breaks down rock, creating ions.
The ions are carried by streams and rivers, reaching the oceans. Chloride and Sodium make up over 90% of all dissolved ions in the ocean. The concentration of salt in seawater (salinity) is about 35 parts per thousand. In other words, about 3.5 percent of the weight of seawater is due to the dissolved salts. However ocean salinity, is the amount of salt concentration within the sea/ocean. Salinity means the rate/ amount of salt. Most of the salt in the ocean come from land. Over millions of years, Rain, River and streams have washed over rocks containing the compound sodium chloride (Nacl) and carried into the sea.
Actual mineral content of river water differ materials from that of the sea. River water contains much of calcium salts (calcium carbonate) than sodium salt. The average salinity is said to be 35% for the whole ocean. Sodium chloride (78%) most important salt in the sea water. However rainfall, evaporation, river run-off and ice formation (melting) cause the variation of salinity in the ocean where by the average of salinity varies between 32 and 37%.
DISTRIBUTION OF OCEAN SALINITY
1. Areas of highest salinity lie near the tropic (about 37%) where skies are clear constant high temperature and brisk trade winds maintain active evaporation.
2. Salinity decrease towards the equator (equatorial) 35% where rainfall is heavier and evaporation less because of the higher relative humidity, greater cloudiness of calmer air masses of the doldrums.
3. There is also a decrease towards the poles (less than 34%), the result of melting ice and decreasing evaporation.
FACTOR AFFECTING THE RATE OF OCEAN SALINITY
1. Climatic condition: During winter season, rain formation, addition of water within the sea reduce the amount of salt while during summer there is high rate of temperature, high effective evaporation of water influence large concentration of salt. Moreover wind direction influence the variation of ocean salnity, the strong winds affect the concentration of water and salt.
2. Ocean current: Is the surface running water within the sea. They are moving in specific channel within the sea. Normally the warm ocean currents make high rate of temperature influence high evaporation and large concentration of salt. While the cold ocean currents make low rate of temperature, poor evaporation and low rate of salt.
3. The amount of fresh water discharge in to ocean: Presence of many river discharge in to the sea reduce the amount of salt since the fresh water tend dissolve and dilute the salt content in to ocean while absence increase concentration of salt.
3. Wideness of the sea: Wide sea leads to large concentration of salt since cannot/difficult to be affected by variation situation.
4. Amount of vegetation cover: Presence of mangrove trees which use a lot of salt reaches the amount of salt in the ocean.
5. Marine organisms: Some organism in the ocean like coral polyps, fish (Whales, dolphins, seals, sea lions)and and other organisms tend to release high salt content especially after died of these organisms.
6. Volcanic activities: The eruption of magma in the ocean can come up with salt content in to the ocean hence this can led to the increase in salt content.
7. Human activities: Human activities like agriculture, fishing, navigation and construction of sewages towards the sea.
8. The nature of ocean basin: The type of minerals contained in to the ocean basin like calcium, sodium and chlorides has high influence towards the ocean salinity.
OCEAN WATER TEMPERATURE
Ocean temperature: Is the degree of hotness or coldness of the ocean water. Normally the ocean water has considerable degree of heat known as sea temperature, the temperature is created as oceans warmed by heat radiated from the sun. However the surface water warmed more slowly than the land, and looses heat to air also more slowly.
FACTORS AFFECTING THE OCEAN WATER TEMPERATURE
Temperature of the sea water varies considerably from region to regions, time to times and depth to depths due to some determinant factors and includes the following:-
1. Latitudin of an area: Amount of solar radiant energy, differs from region to regions. Usually all tropical area experience higher insulation than the Polar Regions as heat radiated from the some received at right angle. Hence the temperature of the ocean in equatorial region is higher at about 26 and gets progressively low towards the poles.
|
Latitude
(North and South) |
Average temperature |
|
Equatorial region |
20°C |
|
20° |
23°C |
|
40° |
14°C |
|
60° |
1°C |
|
Polar region |
|
2. Local cloud covers: The clouds tend to absorb the heat radiated from the sun to the water surface, It is thus, if clouds make intensive coverage lower the sea temperature.
3. The sun’s altitude from the water surface: If the sun’s altitude is greater enough to the earth’s surface more heat from the sun is scattered and absorbed on the way before reaching the earth surface at which absorbed. It is thus: the marine water in tropical regions is warm as the sun’s altitude is small to the surface compared to polar seas like that of Arctic seas.
4. Distance of the earth from the sun: When the earth is at farthest position from the sun, less heat received by the earth surface and makes low sea temperature, Conversely, when the sun is at nearest position, more heat received and makes high sea temperature is much based on the sun over head. In the same geographical region. The sea temperature can vary time to time depending on the prevailing season whether or winter.
5. Ocean currents: Warm ocean currents maintain steadily higher temperature by warm water brought into the area. Cold ocean currents lower sea temperature.
6. Atmospheric absorption an scattering: If more heat from the sun scattered and absorbed in the atmosphere, make low sea temperature as less heat reach the surface and absorbed. Conversely, if less heat scattered and absorbed sea temperatures become high as more heat reach the surface.Man made influences
7. Human influence: Man-made influences on water temperature include, thermal pollution, runoff, deforestation and impoundments.
i. Thermal Pollution: is any discharge that will dramatically alter the temperature of a natural water source. This pollution commonly comes from municipal or industrial effluents. If the temperature of discharge is significantly warmer than the natural water, it can negatively affect water quality. There are several significant consequences of thermal pollution, including diminished dissolved oxygen levels, fish kills and influxes of invasive species.
ii. Run off: from parking lots and other impervious surfaces are another form of thermal pollution. Water that flows off of these surfaces absorbs much of their heat and transfers it to a nearby stream or river, elevating the temperature.
iii. Deforestation: It is not only manmade additions that can affect water temperature. Water that is shaded by vegetation and other objects will not absorb as much heat as sunlit water. When trees or riparian canopies are removed, a body of water can become unusually warm, altering its natural cycle and habitats.
IMPORTANCE OF TEMPERATURE IN OCEAN WATER
1. Temperature in ocean water determines metabolic rates and photosynthesis production.
2. Temperature in ocean water determines compound toxicity.3. Temperature in ocean water dissolved oxygen and other dissolved gas concentrations.
4. Temperature in ocean water determines conductivity and salinity.5. Temperature in ocean water determines oxidation reduction potential.
THE OCEAN MOVEMENTS
Ocean movement: refers to the vertical (upward and downward) and horizontal movement of the oceanic water.The ocean water is dynamic they always in motion all the time. Surface water in the ocean basin is not stationary. It moves differently and thus recognized to have varied forms of movement.
CAUSES/FACTORS IN INFLUENCING OCEAN MOVEMENT
The movement of ocean water influenced by the physical factors like:-
1. Variation in ocean temperature: The warm water obvious is less denser while the cold water is more denser therefore the cold water tend to ank down below the warm water hence the warm water moves toward the cold water and cold water moves towards the warm water. The polar cold water move towards the equator and the equatorial warm water moves toward the polar cold water.
2. Variation in ocean salinity: The saline water is more denser than the less saline water, hence the saline (denser) water sink down while the lighter water rise above. Therefore the tropical and Equatorial saline water moves towards the polar while the pola less saline water move towards the Equator and tropical regions dilute the salinity of the ocean.
3. Different in oceanic water density: The denser water sink down while the less denser water rise above the denser water. Hence cause the ocean movement.
4. The gravitational forces between the moon and the sun: This phenomena can contribute to ocean movement through influencing ocean tides.
5. The eclipse: Normally during both the lunar eclipse and the solar eclipse the ocean water tend to be deflected in to different angles which resulted in to the ocean movement.
6. The earth rotation (corriols forces): This is the natural force which cased by the earth rotation when it rotate its axis. Normally the oceanic water tend to follow the direction of the earth rotation which resulted water to be deflected and curculate in to different direction. Therefore oceanic water tend to be deflected and circulate to the right direction (clockwise) in the northern hemisphere and to the left direction (anti-clockwise) in the southern hemisphere.
7. Prevailing winds: High strong prevailing winds influence ocean to move more intetms of waver and ocean currents. Therefore under this context the ocean movement is more affected by the energy, speed and direction of prevailing winds over the oceanic water.
TYPES OF WATER MOVEMENTS IN THE OCEANS
There are two forms of ocean surface water movement which include:-
i. Horizontal movements (Ocean currents)
ii. Vertical movements (waves and tides).
A. VERTICAL OCEAN MOVEMENT
Vertical movements: Refers to the upward and downward movement of ocean water in terms of ocean waves and ocean tides.
1. THE OCEAN WAVES
Waves: refer to upward and down ward movements of sea water. Waves make movement towards the coast and back away from the coast. The forward movement of a wave to the coast is called swash, and the back ward movement is called backwash. Hence swash is the water approaching the coast from the sea, while backwash is the water returning from the coast.
TYPES/ OF OCEAN WAVES
Waves are classified according to causal factors and their nature of effects along the coast.
(a). According to their nature or sources
1. Wind waves: These are the waves produced by the force of wind blow. These are the ones whose swash is more powerful than the back wash and mostly causes the deposition of materials along the shore line.
2. Seismic waves: these are the larger waves generated by the suddenly movement of the oceanic button (sima) usually caused by earth quakes. They ate alternatively called tsunamis. Usually are vibrations (waves of energy) generated by earthquakes. They travel through the Earth like a tsunami travels through the ocean.
3. Tidal waves: These are the waves generated by the gravitational attraction of the moon and sum. They occur when the sea water rises to high tidal level.
(b). According to their nature of effects along the coasts
1. Constructive waves: These are the waves whose swash is more powerful than the back wash and mostly causes the deposition of materials along the shore line.are flat and low in height and have a long wavelength. Their strong swash carries material up the beach, forming a berm. They have a low frequency of between 6 and 8 waves per minute. The wave energy dissipates over a wide area which results in a weak backwash.
Characteristics of constructive waves
i. They are created in calm weather and are less powerful than destructive waves.
ii. They break on the shore and deposit material, building up beaches.
iii. They have a swash that is stronger than the backwash.
iv. They have a long wavelength, and are low in height.
2. Destructive waves: are the waves whose backwash is more powerful than swash and mostly causes destruction along the shore a line. Destructive waves have a large wave height and short wavelength. They have tall breakers that have a high downward force and a strong backwash. Their frequency is high with between 13 and 15 waves per minute.
Their strong downward energy helps erode beach material and cliffs. The strong backwash results in narrow beach profiles.
Characteristics of Destructive waves
i. Destructive waves are created in storm conditions.
ii. They are created from big, strong waves when the wind is powerful and has been blowing for a long time.
iii. They occur when wave energy is high and the wave has travelled over a long fetch.
iv. They tend to erode the coast.
v. They have a stronger backwash than swash.vi. They have a short wave length and are high and steep.
CAUSES OF OCEAN WAVE MOVEMENT
Waves are produced by the following causal factors.
1. The prevailing winds over the ocean surface.
2. The Earth quakes, it can cause the occurrence of sudden uplift of the oceanic bed.
3. Gravitational attraction of the moon and sun. The waves tend to occur as water rise to high tide level.
STRUCTURE OF WAVES
i. Wave trough/syncline: Is the lowest points of a wave.
ii. Wave height: It is the vertical distance from the bottom of a trough to the top of a crest of a wave.
iii. Wave amplitude: It is one-half of the wave height.
iv. Wave period: It is merely the time interval between two successive wave crests or troughs as they pass a fixed point.
v. Wavelength: It is the horizontal distance between two successive crests.
vi. Wave speed: It is the rate at which the wave moves through the water, and is measured in knots.
vii. Wave frequency: It is the number of waves passing a given point during a one- second time interval.
vii. Crest or anticline: Is the upward part of the wave.
2.TIDES
Tides: The periodical rise and fall of the sea level, once or twice per day, mainly due to the gravitational attraction of the sun and the moon. Movements of water caused by meteorological effects (winds and atmospheric pressure changes) are called surges. are the periodic rise and fall in the level of water in the oceans.
Or regular periodic alternating rises and falls of the level of water in the oceans. The rising of water level in a day is called flood tide, while the failing of water level in a day is called ebb tide. Tides commonly occur twice in 24 hours. In day water rises to its highest level and fall to its lowest level to produce high tide (LT) respectively.
The interval between the high tide and low tide levels is called tidal range. Tides are produced as a result of pull of gravity of the moon and the sun, but the pull of gravity of the moon. Contributes more because of being closer proximity to the earth. The sun’s great mass, however causes it to have an appreciable effect, despite its great distance from the earth. The moon attracts or pulls water to the side of the earth nearest to it.
TYPES OF TIDES
A. Tides based on their height
The height of rising water (high tide) varies appreciably depending upon the position of sun and moon with respect to the earth. Tides and neap tides come under this category. Normally, there is a seven day interval between the spring tides and neap tides. At this time the sun and moon are at right angles to each other and the forces of the sun and moon tend to counteract one another.
1. Spring tide: It is the one with maximum tidal range produced when the moon and the sun are in alignment on the same side, increases gravitational attraction production same side, increases gravitational attraction producing the and lowest low tide. This is also known as syzygy tide in basis that, the position when the earth, the moon and the sun are all in straight line is called syzygy period.
The position of both the sun and the moon in relation to the earth has direct bearing on tide height. When the sun, the moon and the earth are in a straight line, the height of the tide will be higher. These are called spring tides and they occur twice a month, one on full moon period and another during new moon period.
2. Neap tide: It occurs when the sun, earth and moon form a right angle with the earth apex as result, the tidal range is made least, This is also known as quadrature tide, in basis that, when the moon, earth and sun are in such a position that they form right angle with the earth apex is called quadrature period. At this position the moon and the sun are pulling the water on the earth to themselves. The result is that, the force of each body is weakened.
The high tide will also be lower than normalThe Moon’s attraction, though more than twice as strong as the sun’s, is diminished by the counteracting force of the sun’s gravitational pull. Once in a month, when the moon’s orbit is closest to the earth (perigee), unusually high and low tides occur. During this time the tidal range is greater than normal. Two weeks later, when the moon is farthest from earth (apogee), the moon’s gravitational force is limited and the tidal ranges are less than their average heights.
When the earth is closest to the sun (perihelion), around 3rd January each year, tidal ranges is also much greater, with unusually high and unusually low tides. When the earth is farthest from the sun (aphelion), around 4th July each year, tidal ranges are much less than average. The time between the high tide and low tide, when the water level is falling, is called the ebb. The time between the low tide and high tide, when the tide is rising, is called the flow or flood.
B. HORIZONTAL OCEAN MOVEMENT
Horizontal movements: The horizontal motion refers to the ocean currents and waves. Ocean currents make horizontal of oceanic water.
THE OCEAN CURRENTS
Ocean Current: is the horizontal movement of surface water in the ocean. Types of ocean currents include:-
i. Warm ocean currents.
ii. Cold ocean currents.
FACTORS INFLUENCING OCEAN CURRENTS
The ocean currents are influenced by
i. Prevailing winds.
i. Differences in oceanic water density
iii. Temperature in oceanic water.
iv. The earth rotation.
v. The shape of the coastlines.
vi. Human activities.
THE OCEAN FLOOR PROFILE
The ocean floor: Is the bottom of the surface of the ocean.
The floor of the ocean is irregular. The major relief features of the ocean floor are;
1. 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.
2. The continental Slope: is found at the point where the continental shelf forms a steep slope towards the ocean floor.
3. Oceanic Deep or Trenches: are long narrow depressions or trough found on the ocean floor.
The deepest ocean trench in the world: is Mariana trench in the southern Pacific ocean.
4. Deep sea plains: Are the most extensive area of the ocean floor.
Parts of deep sea plain
i. Abyssal hills: These are small irregular hiils that develop within the deep oceanic plain.
ii. Abyssal plain: is the plain area which develop between the two abyssal hills within the deep oceanic plain.
5. Ocean ridge: is part of the ocean floor rasing towards the sea level. Normally the oceanic ridges are characterized by having some features like plateau and volcanoes.
6. Island: is the part of ocean floor rising above the sea level.
Types of islands
i. Coral island: Are the islands which formed by limestone rocks as the result of accumulation of skeleton of very small marine organisms called coral polyps. Example of coral islands are such as Maldives, Al dabara, Bermuda and Martinez Islands.
ii. Continental islands: these are large type islands which rising from continental shelf and occupying large geographical area like a continent. E.g Pemba and Unguja, Mafia, Philippine, Indonesia, Greenland and Sir Lanka.
iii. Oceanic islands: These are islands rising direct from the ocean floor. Some of these island are the tops of oceanic ridges, plateaus and ocean floor volcanoes. Example: Hawaii, cape Verde, Iceland, Canary and Seychelles.
NB: The lowest part of the earth/deepest ocean trench in the world is Mariana Trench in south Pacific ocean.
GUIDING QUESTIONS
1. Name major seven continents in the world starting from largest to smallest
2. List down five main rivers in Africa. The main rivers in Africa are:-
