COAST AND COAST EVOLUTIONS – ADVANCED PHYSICAL GEOGRAPHY
What is the coast?
Coast is the strip of the land bordering the land and sea. OR
Coast is a narrow zone where the land and the sea or ocean meet or overlap and directly interact.
What is the coastline?
Coastline is the border between land and sea.
What is the shore?
Shore is the land between the high tidal water level and low tidal water level.
What is the shoreline?
Shoreline is the line where the shore and the sea meet.
What is the beach?
Beach is the part of land comprised by sand and shingle located on the shores. OR
Beach is the wider strip of sand or shingle deposits with water along the sea coast.
COASTAL EVOLUTION
Is the structural change in the appearance of the coast line from place to place or time to time. For example, Zanzibar coasts differs from that of Dar es Salaam.
FACTORS INFLUENCING THE COASTAL EVOLUTION
Why Dynamism of the Coastlines (Dynamic nature of the coast)
The coasts keep on changing due to the following factors. These are:-
1. Action of waves and tidal currents:
These affects the coastal appearance as they influence erosional and depositional. Wave erosion lead to erosional features along the coast such as notches, caves, etc. While wave depositional along the coast lead to the formation of depositional features like sandbars, beaches, spits, etc.
2. Tectonic activities and volcanic activities:
These can lead to the upward or downward movement of the landmass along the coastline which may result from volcanic eruption. The uplift of the coast can lead emerged of the coast while the down lifting of the coast causes the submerged of the coast. Hence coasts are dynamic.
3. Nature of rocks along the coast:
the rocks can lead the structural changed of the coasts. For instance, the alternate hard and soft rocks may result into formation of bays and gulfs with head land. Where coasts made by resistant rocks they produce steep coasts with cliffs while soft rocks produce low land coasts.
4. Human activities:
Activities by the man like mining, land reclamation, construction of canal and harbours can produce the structural changes of the coasts eg. Holland.
5. Glaciation:
The glacier activities like erosion along the coast produce features example fiord coast. Also, the melting of ice near the coast can lead to rises of the sea level as results of submerged coasts formation.
6. Organisms:
Some coasts are organic in nature like coral coasts, as they characterised with formation of reefs which are dead remains of coral organisms.
7. Topography:
This is the important since the gently sloping shoreline can influence deposition features while steep sloping shorelines can influence erosion features.
8. Global warming:
It is another factor that leads to the melting of ice hence result into changes of the coast due to the formation of barrier beach and delta.
SEA LEVEL CHANGE/EUSTATIC CHANGE
Eustatic changes are the global sea level changes related to changes in the volume of water in the ocean. Globally, sea level has risen to approximately 120 m since past glacial maximum approximately 20,000 years ago. However, from 1901 to 2010 the sea level rises at the rate of 1.5 to 1.9 mm per year.
CAUSES OF THE SEA LEVEL CHANGES
The sea level changes caused by the following factors. These are: –
Glaciation;
Severe freezing of water and large-scale melting of ice causes changes in the level of the sea eg. during and post glaciation.
Global warming and climatic changes;
The rise global temperature cause melting of glacier and ice caps as a result more water discharged into the ocean, hence changes in sea level
Isostatic changes;
Isostatic may cause change in sea level due to effects on land subsidence the sea level rises and when the land uplifted the sea level fall.
TYPES OF THE EUSTATIC CHANGES
There are two (2) types of eustatic changes. These are;
Positive eustatic changes;
This is the rises of the sea level relative to the fall of the land surface. Positive sea level changes cause formation of ria and other submerged coast.
Negative eustatic changes;
This is the fall of the sea level relatively to the land. This movement characterised with exposure of sea level.
EVIDENCE OF EUSTATIC CHANGES
i. Geomorphological evidence;
These are features result from submergence and emergence of the coast resulting from the rise and fall of the sea. These features like;
i. Formation of estuarine coast eg. at river Congo.
ii. Formation of ria coast eg. at coast of Dar es salaam.
iii. Formation of Dalmatian coast
iv. Formation of fiord coast, and
v. The raised beaches along the coastal area.
vi. Exposure of mud flats and wave cut platforms, etc.
ii. Archeological evidence;
The best examples are the submerged of Roman pavement in south Sweden.
iii. Botanic evidence;
Presence of peat formed due to the submerged of forests on the coast of Wirral peninsular in North Wales.
iv. Rejuvenation of river.
Most of the river at lower course have been undergoing rejuvenation process to signify fall of ocean level.
v. Balance between erosion and deposition at the river mouth, etc.
CLASSIFICATION OF COASTS
The coasts are classified differently like as follow;
i. Classification of coasts based on the sea level changes.
ii. Classification of costs based on the nature of rocks.
iii. Classification of coasts based on the structural trend (appearance) of the coasts.
iv. Classification of coasts based on the relation of advancement and retreatment of the land.
v. Classification of the coasts based on the materials composition of the coasts.
I: CLASSIFICATION OF COASTS BASED ON THE SEA LEVEL CHANGES
In this category the coasts divided into four types. These are: –
- Emerged coasts.
- Submerged coasts.
- Stable (neutral) coasts.
- Compound coasts.
A: EMERGED COASTS
These are the coasts have been produced after the fall of the sea level and rises of the coastal land.
TYPES OF EMERGED COASTS
There are two subtypes of emerged coasts. These are;
1. Emerged low land coasts:
These are the lowland coasts formed when part of the lowland areas along the coast emerged due to the fall of the sea level or uplift of the land.
Characteristic features of emerged lowland coasts;
i. Rejuvenation of the river.
ii. Formation of sea shore, mudflats, offshore bar, beaches, and barrier beaches.
iii. Emergency of old coastline and old beaches.
2. Emerged high land coasts.
These are the coasts produced after the lower part of the highland areas to become out of water as a result of falling of the sea level or uplift of the land.
Characteristic features of emerged high land coasts;
i. Raised beach. It is found beyond the present shoreline
ii. Old and new notch. It formed due to undercutting of a cliff by wave erosion.
iii. Wave cut platform. It extends above the present shoreline.
iv. Old cliff. It standing above the new cliff.
B: SUBMERGED COASTS
These are the coasts whose lower parts flooded by the sea water due to rises of the sea level or fall in the land surface along the coast.
TYPES OF SUBMERGED COASTS
This coast can subdivide into two subtypes. These are;
1. Submerged lowland coasts.
These types of coasts produced when lowland gets submerged by the sea water.
Example of submerged lowland coasts;
i. Estuarine coast.
This is a submerged low land coast, formed when the mouths of the river (lower part of river valley) along the low-lying coast are drowned (flooded) by the sea water. As a result to the formation of funnel shaped estuaries. Example river Thomas in England.
2. Submerged highland coasts.
These are coasts produced when parts of upland coasts get drowned by raised of the sea level
Types of submerged highland (Upland) coasts;
Ria coasts.
These are the highland coasts formed when lower part of river valley in highland drowned by the rise of sea level and producing ria coast. Rias coast have funnel shaped opening covered by deep water and make natural harbour. Example of ria coasts like north west France, north west Spain, and south west Ireland. It is also Dar es salaam harbour.
Dalmatian (Longitudinal) coasts.
The highland submerged coast formed when part of mountain valley parallel to the coast get submerged by the rise of sea level. The mountain between valley become chain of Isles and swallowed with water give narrow inlet. Good example of these coasts in Yugoslavia, and north and south America.
Fiord coasts.
This is a long narrow steep sided and deep-sea inlet along the coast. It is formed due to submerged of glaciated U-shaped glacier valley by sea water. It is characterised by a valley with steep walls with several tributaries joining the main valley. Fiord occur in Scandinavia coast and Trondheim is a good example. Also occur in Chile and New Zealand. If the fiord entrance there occurs accumulation of moraine called threshold.
C: STABLE/ NEUTRAL COASTS
Are the coasts showing no signs of changes in sea level or in the land but influence coastal land slowly. In these coasts the incidental erosion process is a reversible process representing the condition in which the coastal profile is restored.
D: COMPOUND COASTS
These are coasts produced due to the influence of a mixture of several emergences and submergences as well as other effects like accumulation of materials.
II: CLASSIFICATION OF COSTS BASED ON THE NATURE OF ROCKS
In this category the coasts divided into two types. These are: –
Indented coasts:
Are the coasts made up by alternative layer of soft and hard rocks structure.
Smooth coast.:
Are the coasts made up by the uniform rock structure.
III: CLASSIFICATION OF COASTS BASED ON THE STRUCTURAL TREND (APPEARANCE) OF THE COASTS
In this category the coasts divided into two types. These are: –
Discordant coasts;
Are the coasts whose relief structure such as mountain and valley lie at right angle to the coasts and seas example Fiord coasts. There are many discordant coasts along the Atlantic Ocean.
Concordant coasts (accordant coasts):
Are the coasts whose structural trend of mountain and valley are parallel to the ocean and sea.
They very common along the Pacific Ocean.
IV: CLASSIFICATION OF COASTS BASED ON THE RELATION OF ADVANCEMENT AND RETREATMENT OF THE LAND
In this category the coasts divided into two types. These are: –
Advancing coasts:
Are the coasts whose level extend as a result of marine deposition, uplift of the land and land reclamation. Example highland coasts.
Retreating coasts:
Are the coasts that appear to diminish due to marine erosion or submergence of the coastal lands.
V: CLASSIFICATION OF THE COASTS BASED ON THE MATERIALS COMPOSITION OF THE COASTS
In this category the coasts divided into two types. These are: –
a) Organic coasts
Are type of coasts made up by deposition of organism remain. Example coral coasts. It is characterised by presence of coral reefs.
b) Inorganic coasts
Are the coasts made up by mineral rocks like volcanic mineral through volcanic eruption. Example volcanic coasts.
CORAL REEFS
What is coral?
Coral is a general name for any of a large group of marine organisms with calcareous skeletons.
What is the coral reef?
A coral reef is a limestone rock which are made of calcium carbonate and calcareous algae formed when coral polyps die.
What are the polyps?
Polyps are tiny sea creatures of many colours and shapes, some with sponge-like shapes, while others are smooth and rounded with a hard skeleton of calcium carbonate.
FORMATION OF CORAL REEF COASTS
When coral polyps die, their skeleton made of calcium carbonate accumulates to form coral limestone. Calcareous algae which precipitates calcium carbonate helps to cement the space between the skeleton.
Thereafter, the skeleton is compressed and compacted under its own weight to form a coral reef. The process of piling up of skeletons, compressing and compacting them by using their own weight helps to form masses of rocks called coral reef coasts.
CONDITIONS NECESSARY FOR THRIVE OF CORAL REEFS
i. Availability of oxygenated water for polyps to live.
ii. The sea temperature should be not less than 210C and not exceed 300C.
iii. There should be plenty of sun light that reaches the depth of sea about 50m to 60m, beyond this depth sunlight is too weak for photosynthesis.
iv. They need salt water and clear free from sediments, therefore cannot grow at the river mouth.
v. It requires plentiful supply of plant food (planktons)
DISTRIBUTION OF CORAL REEFS
i. In tropical oceans latitudes between 30°N and 30°S of the equator where temperature is not less than 21°C.
ii. On the eastern sides of continents where warm ocean currents flow. Hence, Coral coasts are widespread in East African coasts, especially in Zanzibar and Bagamoyo coasts.
Therefore; they do not develop on the west coast of land masses because of the cool ocean currents which flow along these areas.
THE FARMOUS CORAL REEF AREAS OF THE WORLD
The most famous coral reef areas of the world are;
i. The Great Barrier Reef
This is the largest coral reef system commonly found the Queensland and parts of the coast of Australia.
ii. The Belize Barrier Reef
This is the second largest coral reef of the world that covers along the western Atlantic coast such as Bermuda, the Bahamas, Florida and Caribbean islands.
iii. The Andros Bahamas Barrier Reef
This is the third largest coral reef of the world that covers the east coast of Andros Island, and the Bahamas in Burma
iv. The New Caledonia Barrier Reef
Is another largest dominant coral reef of the world that covers almost the length of 1500km.
v. The Indo Pacific coral reefs
These coral reefs cover vast area from the coast of east Africa to the Persian Gulf through the Indian and Pacific Oceans.
TYPES OF CORAL REEF
There are three types of coral reefs. These are: –
- Fringing coral reef.
- Barrier coral reef.
- Atoll coral reef.
A: FRINGING CORAL REEF
Is the coral reef which separated to the coast by a shallow and narrow lagoon. The seaward edge sloping down into deep water falls steeply to the sea floor.
The distance of the reef from the shore ranges from 450 metres to over 1800 metres. It is found along the coasts of Tanzania and Kenya. Despite being evident in Tanzania and Kenya, the fringing reefs extend from Mozambique to Somalia.
B: BARRIER CORAL REEF
This is the coral reef which separated from the shore by a wide and deep lagoon. This is normally located several kilometres away from the shore.
A good example of a barrier reef is Mayotte Island located between Malakasis and Mozambique.
C: ATOLL CORAL REEF
This is a circular-elliptical or horse shoe shaped coral reef enclosing a lagoon without islands in between.
Atolls are common in the Pacific and Indian oceans. Some atoll reefs are very large, for example, the Suradiva in the Maldives which is 64 km long. The best example of an atoll in Africa is the Aldabra atoll that lies between Zanzibar and Madagascar about 700 km from the African coast.
IMPORTANCE OF CORAL REEFS
1. They provide good fish breeding grounds;
2. They attract tourists who contribute to the national income and in turn boost the economy of the country. Mbudya Island in the Indian Ocean near Dar es Salaam and numerous coral reefs sites in Zanzibar are good examples of coral islands that attract tourist;
3. They provide habitats for sea turtles, algae and fish;
4. They act as raw materials in pharmaceutical industries, for example, the production of Plaster of Paris (P.O.P); also;
5. They are used as raw materials in manufacturing of cement and gypsum powder;
6. They protect coastlines from erosion, flooding and storm damage; and (f) They are used for decoration.
PROBLEMS CAUSED BY/DISADVANTAGES OF CORAL REEFS
1. They hinder development or occurrence of natural harbors
2. They are barriers to navigation since they tend to lead to the development of shallow lagoons;
3. They block waves hence hindering development of erosional and depositional features like beaches and curves which can be tourists’ attractions; and
4. Coral masses discourage swimming in the sea or oceans. Diving in coral coasts is dangerous.
THREATS/PROBLEMS FACING THE DEVELOPMENT AND GROWTH OF CORAL REEFS
The following are the problems facing the development and growth of coral reefs.
These are: –
1. Strong winds lead to the formation of destructive waves hinder the development of coral reefs.
2. Oil spills, acid rain, poor fishing methods like uses of chemicals lead to destruction of coral reefs and death of coral polyps.
3. Breaking of coral rock for manufacturing of cement, and getting stones for construction affects growth of coral.
4. Deposition of mud by a river along the coast hinder growth of coral reefs.
5. Poor of coastal management policies and laws hinder the growth and development of coral reefs.
6. Fall of the sea level affect the development of coral reefs.
7. Increasing of temperature due to global warming is attributed to coral bleaching.
ORIGIN AND FORMATION OF CORAL REEFS
The origin of coral reefs is associated with the following theories. These are; –
1. Subsidence (Darwinism) theory.
2. Murray’s theory on coral formation (Stand still theory).
3. Dally’s theory (Glacier control theory).
1: DARWINISM (SUBSIDENCE) THEORY
This theory provided in 1842 by British scientist named Charles Robert Darwin. According to this theory, all coral reef began as fringing reefs around volcanic island.
Due to Island slowly subsidence due to down warping of the earth’s crust, the coral continues to grow upwards to keep pace with the subsidence as a result of barrier reef formation. Eventually, when the land is completely submerged, the atoll is formed enclosed with shallow lagoon.
STRENGTH OF DARWINISM THEORY ON CORAL REEF
- It gives sight for further research about the coral formation.
- Evidence of Bikini and Eniwetok coral Isles in the Pacific Ocean which are underlined by volcanic rocks.
WEAKNESS OF DARWINISM THEORY ON CORAL REEF
i. The theory failed to explain the causes of sinking of Island.
ii. It presupposes the idea that barrier must form around an Island and not mainland
iii. No clear explanation why atolls are formed in Deep Ocean.
iv. Characteristics in Timor reef have been obviously uplift beyond the present sea level.
2: MURRAY’S THEORY ON CORAL REEFS (STAND STILL THOERY)
It was provided in 1872 by British scientist Sir John Murray. According to this theory, the formation of Atoll s due to accumulation of pelagic material (coral debris) on submarine hill or plateau which rises on oceanic floor that grow upward to form Atoll. The formation of Barrier reef is due to erosion by waves against Fringing reef along the coast, where by the broken materials accumulated seaward to form base at which coral grow.
STRENGTH OF MURRAY’S THEORY
i. It describes possible formation of atoll in the mid ocean
ii. It clearly some doubts of Darwinism theory. Example formation of atolls in deep oceans.
WEAKNESS OF MURRAY’S THEORY
i. Scientist doubts on accumulation of pelagic materials is the slowly, hence could not build atoll bases.
ii. Fragment broke from fringing reefs could not build up steep reefs.
3: DALY’S THEORY ON CORAL REEF (GLACIER CONTROL THEORY)
It was provided in 1915 by scientist named Daly. The theory describes the possible of coral formation due to rise in sea level during and after ice age.
During the glaciation; the sea was very cool so that the coral and Isles were destroyed due marine erosion. At this time the sea level falls about 300feets.
During the late and post glaciation; the sea level rises due to glacier melt, hence leading growth of coral previously eroded.
STRENGTH OF DALY’S THEORY
1. It helps to describe the narrow and deep sided reef, and formation of atoll.
2. Evidence brought from Funafuti and Ellice Isles favour the formation of corals due to sea level changes.
THREATS/PROBLEMS FACING COASTAL AREAS
i. Water pollution caused by disposal of untreated waters like sewage and water containing chemicals from industries and agricultural areas.
ii. Oil spills from tanks.
iii. Excavation of sand and rocks (Mining activities)
iv. Poor fishing methods like using dynamites fishing.
v. Land degradation caused by wave erosion and river rejuvenation which attacks the coastal lands hence discourage formation of coral reefs.
vi. Floods caused by the occurrence of storms, tsunamis and the change in sea level due to melting of ice or land subsidence.
vii. Unpleasant smell from the sea due to water pollution makes some coastal areas unfriendly to users eg. at Kivukoni (Posta) area in Dar es salaam.
viii. Occurrence of volcanic activities along the coast due to earth movements may destroy coastal areas and pollute water.
ix. Deforestation may be caused by excessive cutting of trees or soil degradation affect development of coastal areas.
WAYS OF COAST MANAGEMENT
The following are the solution measures for coastal conservation. These are: –
i. Construction of groynes (low walls) can help to minimize beaches, roads passing near the coast, and stabilizing cliff from being degraded by severe wave erosion.
ii. Planting of vegetation especially mangrove trees and grass which provide a uniform stabilizing cover that protects the surface along the coast. iii. Prohibiting people from establishing settlements and cultivating in the coastal areas.
iii. Formulating coastal management policies and educating the people in the coastal areas on the importance and ways of conserving coastal areas.
iv. Discouraging waste disposal in the oceans, and encouraging treatment of waste before being disposed into the oceans or seas.
v. Recycling of waste should be encouraged so as to reduce the rate of damping in the ocean especially solid waste.
v. The government should open up opportunities for different economic activities rather than depending much on the fishing industry and marine tourism so as to reduce pressure on the coastal areas.
REVISION QUESTIONS
1. How are the coastal characteristics features related to emerged and submergence of coastal lines?
2. Variations in the nature of coastline are essentially the results of number of factors. Justify
3. Describe five environmental problems facing the coastal areas and four measures to be taken so as to overcome them. [Necta 2015]
4. What are chief factors which determine the character of coast? (Necta 1973)
5. Examine the factors that have influenced the evolution of coastlines.
6. The present coastline definitely differs greatly from that of the last century. Give a supporting evidences to prove the validity of the above statement (Necta 2009)
7. Comment on the origins and geographical distribution of coral reefs (Necta 1986)
8. “Formation of coral reefs are controversial” Discuss this statement then show five merits of their existences.
9. Explain the formation of coral reefs and give their economic significance (Necta 2011)
10. The coastal zone is undergoing constant changes. Discuss (Necta 1998) 11. Explain the formation of coral reefs and give their economic significance. (Necta 2011)
11. Coastlines are dynamic. Account for the dynamism by using six points.
12. “Coastal landforms are significant to human life” Justify this statement in six points (Necta 2021)
READ FULL NOTES PDF
CLICK HERE TO GET FULL NOTES
