–       -The body of salt water which cover 70.78% of the earth surface.

–       -Is the very wide area on the land surface covered with water. This part of the land should be cover millions of kilometres of water.


–          -As applied to the great body of salt water and earth surface (ocean) as opposed to land


–           -Are the smaller bodies of salt water of the ocean


-A large body of in land salt water for example the sea of Aral.


–           -Is the wide part of land surface covered with water. The sea is intermediate between the ocean and lake in their wideness with salt water E.g. red sea.

  •    The ocean and sea are interlinking with mineral composition the major mineral composed within the sea / ocean are magnesium , calcium ,sodium and other mineral the dominant mineral is the salt.


–          -Is the study of ocean with main interest on the properties of ocean water and its motion

–          -It is also deal with the chemical reaction lives (biodiversity) and the structure of the ocean bed including the process that are active in the ocean.

–          -The ocean regulate in number of major process that operate on the earth`s surface.

–          -They are primary source of the water that reaches the continent as rain and snow.

–          -Contain the largest reserves of carbon which is essential to the biological cycle

–          -Contain / has a high heat capacity that make it  an important regulation of climate (ability to absorb greater quantity of heat )

–          -The movement of water in the ocean (ocean current) is important for both marine and life and human for navigation for many years. That is for transport and communication (wires pass under water )


–          -Topography      -Ocean floor.

Depth of the oceans – About 4,000m (average depth)

Depth of seas   – Is about 1,200m

-In relation to the sea level the ocean are much deeper than the land is high. (Height in depth of ocean is high compare to the land)

– Surface of the earth is only 11%of the land is more than 2000m above the sea level while 84% of the sea bottom is more than 2000m deep.

– The highest elevation that is mountain Everest on the land is 8840m the Marianas Trench in the west Pacific Ocean is 11,000m.

There are 3 major areas in the ocean;

i)                    Continental  margins

ii)                  Deep ocean basins

iii)                Mid oceanic ridges


i)   CONTINENTAL MARGINS – It comprises the continental shelf, continental slope and continental rise.

                      It is divided into;

a)                                         a) The shore

b)                                         b) The continental shelf

c)                                         c) The continental slope

d)                                        d) The continental rise.


a)      Continental shelf

–          -Extension of the continental into the ocean. / Widest around the shores of lowland areas.

–          -Is a gentle slope submerged surface extending from the shores line towards the deep ocean base

–          -It is underlined by continental types crust and therefore it is a Clearly flooded extension of the continent

–          -There is great variation in width and almost non – existed alongside continental and on the average it is about 80km and 130m deep at the sea ward edge.

–          -The average inclination of the continental shelf is lesser than  of1 degree a drop of only about 2m per km the slope is so slight that it would appear the observer to be a horizontal surface.

–          -It is not completely smooth due to presence of extensive glacial deposits in some places and therefore it is rugged/rough.

Prominate features   – Include long valley of many rivers running from the coastline cross the continental shelf into the deep sea water

-Example;   Western Europe and north – Eastern North America


b)      Continental slope  – This area is characterized by a steep gradient compare to the continental shelf

-Marks the boundary between the continental crust and oceanic crust.

-The average inclination of the continental slope is about 5o and in some place may exceed 25o. The average depth vertically from the shelf to the deep sea bottom is on average 4000m.and in some place extend to as much as 9000m vertical over a relatively short horizontal distance.

-Along mountainous coast the continent slope descend abruptly into deep ocean trenches located between the continent and the ocean basin in such a case the shelf is very narrow or non- existence.


The deep ocean basins which are about 2.5 to 3.5miles deep, covers 30% of earth’s surface and has feature such as abyssal plains, deep sea trenches and sea mounts (70% of entire ocean area

·         The abyssal plain – Is the flat deep ocean floor. It is almost featureless because thick layers of sediment cover the hills and valleys of the ocean floor below it.

·         Deep sea trenches – Are the deepest part of the ocean the deepest one the Marianas Trench in the South Pacific Ocean is more than 35,000 feet (11,000m) deep.

Topography of the ocean floor - ppt video online download


-The mid ocean ridge is two chain of mountains separated by a large depression (or rift valley) that form a spreading center (or where two plates are drifting apart). The mountain ranges can have peaks as high as 12,000ft (2500m) and some even reach above the ocean surface.

–      -Ice land along the mid – Atlantic ridge is an example.

–      -In the rift valley which can be 15 – 30miles (24 to 48kmwide, new ocean crust is being made which means a lot of seismic activity is happening.

–      -Sea Mountain began life as volcanic formed over hot spot in the ocean floor. After the crust moves off the hot spot the volcanic activity stops.

–      -Sea Mountain is usually 25miles (40km) in diameter and can be 3000 – 4500m tall. Some are so tall that their peaks pierce the ocean surface forming a volcanic island.

Mid-ocean ridge - Wikipedia



NAME AREAS (square meter) AVERAGE depth (m)
PACIFIC OCEAN 60,060,700 4,028
ATLANTIC OCEAN 29,637,900 3,926
INDIAN OCEAN 26,469,500 3963
SOUTHERN OCEAN 7,848,300 4,000 – 5,000
ARCTIC OCEAN 5,427,000 1,205
MEDITERRANEAN SEA 1,114, 800 1429
CARIBBEAN SEA 1,049,500 2647
SOUTH CHINA SEA 895,400 1652


–          -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.


Distribution of salinity

–          -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%.

–          -Areas of highest salinity lie near the tropic (about 37%) where skies are clear constant high temperature and brisk trade winds maintain active evaporation.

–          -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.

-There is also a decrease towards the poles (less than 34%), the result of melting ice and decreasing evaporation.


            i.   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.

ii.  Ocean current:

Is the surface running water within the sea. They are moving in specific channel within the sea.

Types of ocean current.

–  Warm ocean current.

High rate of temperature influence high evaporation and large concentration of salt.

–  Cold ocean current.

Low rate of temperature, poor evaporation and low rate of salt.

Revealed: The Effects of Ocean Currents on the Earth's Climate ...

            iii.  Amount of river stream within the sea.

Presences of river entering the sea reduce the amount of salt and absence increase concentration of salt.

            iv.  Wind action.

Strong winds affect the concentration of water and salt.

             v.  Wideness of the sea.

Wide sea leads to large concentration of salt since cannot/difficult to be affected by variation situation.

             vi.  Amount of vegetation cover.

Presence of mangrove trees which use a lot of salt reaches the amount of salt in the ocean.


-The water of the ocean 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.

-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.      Latitudinal position  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 26and gets progressively low towards the poles.



(North and South)

Average temperature
Equatorial region




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.


-Surface water in the ocean basin is not stationary. It moves differently and thus recognized to have varied forms of movement.  There are three forms of ocean surface water movement and include the following.

·         i.Waves

·         ii.Tides

·         iii. Ocean currents


– Waves and tides make vertical movement of oceanic water.

– Ocean currents make horizontal of oceanic water.


Waves refer to upward and down ward movements of sea water. Waves are produced by the following causal factors.

·             -Transfer  of energy by the  wind blowing over  surface of the  sea.

·             -Earth quakes refers to the occurrence of sudden uplift of the oceanic bed.

·             -Gravitational attraction of the moon and sun. The waves tend to occur as water rise to high tide level.


The structure of the wave

-The structure of a wave is by its contrasting parts.

·         -The upward part of the wave s called crest or anticline.

·         -The lower part of the wave is called trough or syncline.

·         -The horizontal distance from a crest to another successive crest is called wave light. The vertical distance between the crest and trough is called

-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

File:Water wave diagram.jpg - Wikimedia Commons

Classification of waves

-Waves are classified according to causal factors and their nature of effects along the coast.

According to causal factor waves are classified into the following types

(a)  Seismic waves; these are the larger waves generated by the force of wind blow.

(b   Seismic waves; These are the large waves  generated by the  oceanic bottom (sima) usually caused by earth quakes, They are alternatively called tsunamis

(c)  Tidal waves; these are the waves generated by the gravitational attraction of the moon and sun. They occur when the sea water rises to high tidal level.


According to their nature of effects along the coast waves are categorized into two types

(a      a) 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

(b    b) 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

(c       c) 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

According to their nature of effects along the coast waves are categorized into two types

(a)Constructive waves

These are the ones whose swash is more powerful than the back wash and mostly causes the deposition of materials along the shore line.


(b)Destructive waves

Destructive waves are the ones whose backwash is more powerful than swash and mostly causes destruction along the shore a line.





Tides 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.

Marine Drive, Scarborough, Seascape, Waves, High Tide

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. This creates a bulge or high tide.


Tides are classified according to:

Their varied degree of tidal range

Rate of occurrence in a day

According to their varied degree of tidal range, tides broadly classified into spring and neap tides.

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.


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 normal

According to rate of occurrence per tidal day, tides classified into the following types

1.      Diurnal tides

These are the simplest form of tides characterized by one high water and one low water per tidal day, It is very common in Northern Gulf Mexico and south East Asia

2.      2.Semi diurnal tide

-It is a form of tides, characterized by two high water and two low water per tidal day as the successive high water and low water levels are approximately equal. They occur provides, both the sun and moon are along the equator in a region at varied time per tidal day


3.      3.Mixed tides.

-The form of tides, characterized by having successive high water and low water levels stand differ appreciably i.e. There are higher high water level, and lower high water level as well as higher low water level and lower low water level per tidal day.



-The knowledge of major surface currents comes principally from compilation of mariner’s observation begun in 1840 by the American oceanographer, Mathew Fontanel Maury. It was discovered that, ships courses, are deflected by surface currents. The currents cause discrepancy between ships intended position, and its actual position after it has traveled for a period. With this it was once discovered that, sea surface water have currents. Therefore ocean currents defined as are the movements of surface water masses in the ocean in the ocean basin horizontally covering a considerable distance.

There are two types of ocean currents namely cold and warm currents.

-The cold ocean currents in the world includes; Peruvia, California, West wind drift, Benguela, Canaries, South pacific current, south Atlantic current, south equatorial and Oyashi.

-The warm ocean currents includes; North equatorial currents, North Atlantic drift, North pacific current, Kuro siwo, Mozambique, South Equatorial current, Brazil and Others. The ocean current is produced by the combined factors which are also considered as interplay factors for ocean currents. These include the followings.

1.The world wind belts; the blow of global wind systems over oceans, set up the surface water in motion and thus produce currents. Moreover the directions taken by the wind blow.


2.The temperature of the ocean water; the ocean waters temperature of region produce either cold and warm currents. Cold currents develop in Polar Regions, while the warm currents develop in areas of tropical latitudes.

In Polar Regions the average temperature is around 4 and sometimes is much lower. The water is therefore cooled, descends and moves towards the Equator at great depths in the oceans. In tropical regions where the average water temperature is around 26, the water is heated and expand. Hence ocean water moves away from the area at shallow depth towards the polar.

3.The rotation of the earth;  The rotation of the earth exert the force on the earth’s surface which deflects the movements of objects from their normal position to the right in the northern hemisphere and to the left in southern hemisphere. Hence the movements of ocean water surface are also deflected to the right and to the left in the northern and southern hemisphere respectively.

4.The shape of land masses; The shape(angle)of the coastline affect the direction of water current by redirecting it in certain path. Hence the path taken in any particularly current partly depends on the shape of coastline.   



Sea level change is defined as a variation in the general level of the sea. The average position of the sea in relation to the land has remained relatively constant for the nearly 6,000 years. Before that time, there are had been several changes in the mean sea level. The most dramatic change being as a result of the quaternary ice and plates movement.


Sea level refers to a general level of the sea as if it were influenced by tides of waves.

Sea level changes in classified into

  • Negative changes (negative movements) in which the sea level is falling relative to land level. The coastal land emerges.
  •  Positive changes (positive movements) in which the sea level is rising relative to the land level. The coastal land subsides.

Causes of the sea level changes.

1) Glacial formation and melting of ice.

2) The rising and falling of coastal land i.e. Isostatic movements.

3) Eustatic change can also be caused by the change in the size of the ocean basin.

Coastal Scenery resulting from changes in the sea level

Relative move of the sea level can be grouped into negative and positive as mentioned earlier .

-Negative movement produce Emerged coasts   

-Positive movements produce submerged coasts



-Occurs when highland along/near the coast lines become submerged (sinking of the land).

a) RIA coast

This is the coast which is formed when the highland area with level valleys is submerged and the lower parts of its river valley becomes flooded by water from the sea. The submerged river valleys are called rias, formations of harbors. E.g.  Between Sierra Leone and Gambia, coast of guinea Bissau West Africa. Mombasa and Dar coast (harbors)



b)     Fiord coast

This is formed when glaciated U-shaped valley are flooded after the submergence of former coastal highland. The flooded glaciated U-shaped valleys are called fiords.  E.g. Alaska in U.S.A, South island in New Zealand, Fiord in Chile.

c)   Dalmatian/longitudinal coasts

-Coasts formed/found in regions made up of hills and valleys which lie parallel to the coast are submerged. After submerged; – The valleys which are between the mountains are flooded. The flooded valleys are called sounds and mountain ranges become chains of island E.g. Dalmatian coast in Yugoslavia.

Submerged coast in lowland

a) Estuarine coast –flooded parts of river valley at their mouth.
-Formed when the lowland area along the former coast is submerged due to penetration of water inland after the rise sea level. The submergence leads to the formation of the feature like estuaries. Estuaries coast are formed when the river mouth is drowned.


-Form when the lands under water (continental shelves) become dry land by uplift. /formed where there is a relative fall in the sea level leads to emergence of larger part.

Emergent upland (of the continental shelf)

i) Raised beaches – These are the beaches which stand above the present shore in Mombasa


ii)Wave – Cut Platform:
-These are platform like features standing above the present shoreline.

-These are v- shaped cut formed as of undercutting of a cliff during the high tide on the emerged coast.

iv)Old Cliff:
-Is the cliff which stands above the next cliff.



-Type of coast where by the structure trend of the land is parallel to the coast, in this the highland like mountain and valleys run parallel the direction of the coastal alignment e.g. Dalmatian of Yugoslavia.


-Type of coastal where by the structure trend of land is at height angle top the coast. It is mountain and valley running at right angle to coast. Example fiord coast in the Scandinavian

Classification of sea level changes.

  • Sea level change is classified into two basic types according to the causal factors influenced it to occur and include.

i. Eustatic Sea levels change

It is the variation in the general level of the sea taking place at a global level (worldwide) usually caused by either melting of ice or severe freezing of water. Severe freezing of water causes the rise in sea level as more water discharged into the ocean basin.

ii. Isostatic sea level change

-It is the local variation of the sea level caused by he changes in the level of land as a result of earth’s movement. When land rises, sea level falls, and when the land level falls sea level rises.

  •  Sea level change is also classified as positive and negative change:

Negative change is the fall of the sea level relatively to the land level while
positive change means the rise of the sea level



The geomorphology evidences are principally to the features related to submerged and emerged coasts resulting from the rise and fall of the sea level relatively to land level.

The features associated with the submerged coasts include the following:-

(i). Estuarine coast.

It is a low lying coastline with a fully flooded river valley. The feature is produced as the low lying coastline with river valley submerged following the rise of the sea level making the valley of the river fully flooded by the oceanic water.

Where estuarine coast found, it becomes difficult to recognize the levels of the river and sea. The most classic example of estuarine coast in the world is that of Thames coast in England


(ii). Ria coast.

             It is highland coastline with a partially flooded river valley. It results where a coastline of high level with river valley submerged as sea level rises making of rises making the lower parts of the valley flooded. Ria  coasts are common in SW  Ireland, SW England and New Spain


(iii) Longitudinal coast.

It is a coastline lies parallel to the submerged valleys of mountain chain.

Where highland coast whose mountain valleys parallel to the coast, after submergence, the valleys will be flooded and the mountains separating the   valleys, become chains of island. A good example of Dalmatian coast, is the coast of Yugoslavia


(iv) Fiords.

Fiord is a long narrow steeply sided and deep sea inlet along the coast.  A coast line with this unique feature,  is called fiord coast. Fiords were produced by the drowning of glacial troughs after submergence. A good example of fiord is that of  also in Norway

 The features associated with emerged coastlines include the following

(i)               Offshore features like beaches

These were produced after the low land coast to have been emerged. The emerge of the coast makes the features which were along the shore line to appear out of the shoreline as a new shore line formed. Off features are more observed along the Gulf of Mexico.

(ii)               Raised features

The features which appear high enough away from the sea. These have resulted after the high land coast to have been emerged. These include mostly the raised beaches. E.g. Raised beach in western Scotland.


It is much based on Neolithic settlements and Roman pavements in the Southern Sweden, which appear below the present low tide mark.



It is principally to the finding of peat, formed due to the submergence of forests on the coast of Wirral peninsula nearly Harleth in North Wales.



Most of the rivers at lower courses characterized by having gentle or general level gradient giving to low water velocity. Some rivers have high water velocity which indicates that, the gradient of water flow has increased due to the fall of sea level relatively to the coast land.


Ocean water supports the life of organisms because of its aquatic eminent. The aquatic environments  provide organisms with important gases nutrients,  food and other important requirements

The organisms found in marine water are of both, plants and animals


Organisms in the marine aquatic ecosystems are of married nature, and also have varied habits. By being varied in such aspects, organisms broadly    categorized into the following forms.


According to their habits, marine organisms include the following groups

        a. Benthos

These are the organisms living on or in the ocean bottom (benthic environment) some live on bottom sediments. And called in fauna. And others live near bottom water called epifauna. Examples of benthos include; marine warms, mollusks, crustacean, star fish and others. Generally speaking, benthic organism is far more abundant in shallow water than on the deep ocean bottom.



        b. Nektons

These are the free swimming animals, they are more abundant in near surface waters, but occur at all depths in the ocean. Many types of nekton organism have regular daily vertical migration, At night they swim to the surface water to feed up on the abundant life in this layer. During the day they return to greater depth where they are more difficult to be seen and less likely to be eaten

Some common nektonic organisms


These are the marine organism live at the upper surface layer of the sea. Some live on the water surface, and others live just below the ocean surface neutrons include, Valella, physalia and other related forms of organisms

c. Neutrons

Marine organism according to their varied nature include the following.

1. Plankton

These are the minute pelagic plants and animals that are weak swimmers and can easily moved by currents. Plankton are further divided into:-

(a)    Phytoplankton(plant plankton)

There are the minute single called plants. They live nearly to surface in the environment called euphoric zone, because of requiring sufficient sunlight for photosynthesis,

(b)   Zooplanktons, (Animal plankton)

These are the animal plankton in the marine ecosystem.

2. Marine mammals.

Marine mammals include: Whales, dolphins, seals, sea lions and others. They are warm boded,     breath air and give live birth to their young. These are legless and have streamlined bodies.

3. Sea birds

Sea birds are among of conspicuous and familiar form of marine life. Some  spend nearly their entire  life in the sea, others can barely walk on land, Some  sea birds only use seawater for food. Some fly over the seawater and other swim under water


(Positive significance)

i. Manufacture of drugs and other chemicals from marine organisms, Marine organism contain many biologically active compounds,  that are potentially useful for medical purpose.

ii. Energy electricity is generated by using the tidal range. The rising and falling of water can be used to generate electricity. E.g. At St. Malo in North west France, The electrical energy is known as tidal power .

iii. Parts of the sea can be reclaimed into new land to accommodate more population and give a room for agricultural and industrial expansion

iv. Many resources  are extracted from the sea water, sea water  supplies several materials such as fresh water, salts , bromine, and magnesium water evaporates, Eg North of Malindi – Kenya

v. Extraction of petroleum and natural gases.  These have been formed by decomposition of the plant materials primarily marine plants. Hence they have been formed by submerged deposits.

vi. Oceans are the source of fish everywhere in the world.

source of fish


vii. Allow the sailing of large vessels of ships. It saves as an important route way connecting the widely separated parts in the world.


viii. Used as sewage disposal system.

ix. Tourism Oceans provide sites for a variety of recreational activities. These include. Swimming surfing, water skiing, sport fishing, and cruising e.g. tropical seas are a tourist attraction because they are warm all year around.


x. Port development. Some features on the submerged coasts favor the development of deep and well sheltered natural harbors. E.g. Fiord coast in Norway

Port development

(Negative significance)

i. Infertile soils. Some emerged coastal lands are characterized by sand, gravel and bare rock, such surface cannot support proper plants growth because they are infertile.

ii. Transport barriers; deposited  sands, sandbars and coral reefs are a barrier to water transport, Sometimes, ships have been wrecked after hitting some of those features.



-Coast refers to the part of the landmass that is situated immediately after the sea. It is separated from the sea by a shore line. Shoreline means, a piece of land that lies in between of high tide and low tide levels.



Coast evolution means, the structural change in appearance of the coastline. Usually the structural appearance of coast varies from place to places or time to times. E.g. the structural appearance of Dar es Salaam coast differs from the Bagamoyo. The structural appearance of Dar es Salaam coast currently, is not the same as it was in many years ago. Hence the phenomena of the coast to change in it structural appearance place to place or time to time geographically described as coast evolution

The evolution of a coastline is brought by one or combination of two or more of the following factors.

1.   Wave action

Wave has a considerable impact to a coastline structural change through the activities of erosion and deposition. Wave erosion may cause a coast line eroded to have features of marine erosion of like; cliff, notch, stacks, bay and others of the same consideration. Wave deposition may cause a coastline developed with features of marine deposition of like; beach, barrier beach, spits, tombolo and others.

Wave action

2.   Tectonic forces.

Tectonic activities have changed and may continue to change the form of appearance of coast lines through uplifting and sinking relatively to sea level. Uplift of a coast line, produces emerged coastline. Down warping produces the submerged coastline.

3.   The nature of rocks along the coast

A coastline may change partly because of its nature of rocks along. For instance: the coastline with alternative rocks of hardness, one subjected to erosion, may change into indented coastline as it can be compared to a coastline of uniform rock hardness.

Beside to this, where the coastal rocks are resistant to erosion a highland coast is formed with cliffs.

4.   Man activities

Human activities of like land reclaim nation harbors construction, canals construction change the natural appearance of coastlines. For example: the land reclamation in Netherlands, have changed the form of appearance of coasts along the North Sea.

5.   Volcanic activities

Eruptions of volcanoes have caused some coasts to change in physical appearance as landforms related to the geological phenomena form along the coasts.

6.   Glaciations.

It is considerably on the occurrence of glaciers along the coast. This leads to coast evolution in two varied ways. Firstly; the melting of ice has caused the rise of general sea level, and then made parts of coasts to immerse in water, and thus submerged coasts have been formed. Secondly glacier activities of erosion and deposition resulted into the occurrence of some physical features related to glacier erosion and deposition.

7.   Organisms

Marine organisms like coral polyps have caused coasts to change in physical appearance as coral reefs develop along them.


Coasts are extremely varied due to several determinant factors of like; marine action, organisms, earth’s movements and others. The earth’s scientists have classified coasts according to their varied considerations.


The most striking criteria which have been employed to classify coasts include the following.

1.   Change in sea level, devoted by Johnson 1919

Neither the level of the land, nor the level of the sea remains unchanged. One of these changed and produced either submerged or emerged coastlines. Considerably to this, coasts are classified into the following forms.

·         Submerged coasts

·         Emerged coasts

·         Neutral coasts

·         Compound coasts


Submerged coasts

These are the coast lines whose lower parts immersed in water due to the rise of the sea level.

Submerged coasts are sub divided into two and include;

·         Submerged lowland coast

·         Submerged highland coast

Lowland submerged coasts form following the fall of lowland coast as the sea level rises. Highland coast produced after the fall of highland coast line due to the rise in sea level.


Emerged coasts.

These are the coastlines that have been produced after the fall of the sea level, and rise of the coastal land. These are also classified into lowland and highland emerged coastlines. Low land emerged coasts are produced after the lower parts of highland  coasts to become out of water as sea level falls while the highland coasts are produced after the lower parts of highland coast to become out of water as sea level changes.

Compound coasts.

Those with a mixture of at least two or more of the features of submerged and emerged coasts. i.e. the coastline is observed to have characteristics of both emerged and submerged coastlines.


2.   According to the structural appearance relatively to other coastal features

With respect to this consideration, coastlines broadly classified into the following types.

·         Discordant coast line

·         Concordant coast line

Discordant Coast line

It is the coastline that extends across the trend of the mountain ranges and valleys. Usually the coastline is irregular with many inlets. Discordant coastline has alternative terms of transverse and Atlantic. The later is because such high proportion of this type of coast is around the Atlantic Ocean.


Concordant Coast.

It is a coastline that lies roughly parallel to the mountain ranges and valleys. When such a coast is submerged, produces the Dalmatian coast. A concordant coast is very common in areas of around Pacific Ocean and that is why they are alternatively known as pacific coasts.


3.   According to the relationship between coast and other processes of erosion and deposition

This was devoted by Sheppard in 1963. According to the approach, gives two types of coast

Primary coasts

The coasts where the influence of sea has been minimum. The coasts characterized by the presence of features not formed by marine action

Secondary coasts

Where marine processes have been dominant. The coasts are characterized by the presence of the depositional and erosion marine features of like.

4.   Advancing and retreating coasts (Valentine 1952)

-It assumes that, a coast can be fitted into two of the following forms.

Advancing coasts

-The coast line that whose level rises as a result of marine deposition or uplift of the land

Retreating coasts

-The coastlines that appear to diminish because of marine erosion or submergence of the coastal land






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