Topic 2: The External Structure of the Earth-Geography Form Two

Topic 2: The External Structure of the Earth-Geography Form Two

EXTERNAL STRUCTURE OF THE EARTH

External structure of the earth consists of four main layers’. These are Atmosphere, Hydrosphere, Lithosphere and Biosphere.

1. THE ATMOSPHERE

Is the thin layer of gases held on the earth by gravitation’ attraction. It composed by abiotic (nonliving matter) and biotic living organism. Non-living matter found in the atmosphere includes mixture of gases, water vapor and dust particles. The living organism include the smallest or microscopic organisms like bacteria

STRUCTURE OF ATMOSPHERE

According to the temperature changes, atmosphere divided into two zones. These are Homosphere and Heterosphere

i) Troposphere

This layer extends by 0 – 15km above the sea level. Troposphere is the first layer of homosphere located nearest to the earth. It contains water vapor, gases and dust particles.

It is the layer of atmosphere which support life on the earth due to the presence of plenty oxygen gas. All processes of rainfall formation take place in this layer and the temperature decreases as the altitude increases at the rate of per every 100 meters or per every 1000 meters.

Note: This situation where by temperature decreases as altitude increases is called lapse rate and because it occur near to the ground is called environmental Lapse rate. The upper limit of Troposphere which separates it to the next later is called Tropopause. Tropopause makes the upper limit of troposphere to the next layer called stratosphere.

ii) Stratosphere

Stratosphere exists between 15 – 48 km above the sea level. This is the second layer of homosphere which lies above the tropopause. It is also composed of water vapor, dust particles and various gases.

It is the layer of atmosphere which characterized by high concentration of Ozonic gases. This gases form Ozone layer which found particularly at 20 –35 km in the stratosphere.

The ozone layer is the layer which form a shield or cover that prevent the earth’s surface from destroying by the sun rays. It prevents the direct incoming of harmful rays from the sun to fall direct on the earth’s surface.

The temperature remains unchanged about between 20 – 35 km from the earth’s surface. Then temperature increases with height to about at the upper limit of stratosphere called stratopause. The increase in temperature with height is referred to as temperature invasion.

iii) Mesosphere

This layer extends between 48-80 kilometers above the sea level. Mesosphere is the third part of the hemisphere where temperature decreases as the altitude increases. It separated from the stratosphere by the zone of separation called stratopause. The upper limit of mesosphere is called mesopause.

Mesopause record minimum temperature of this zone that may fall to making this zone to be coldest. It is at this zone where strong upper air streams of wind like jet streams are experienced.

iv)Thermosphere

Is where temperature increases as the altitude increases from i.e. temperature invasion. This is because there is no water vapor or dust particle in this zone Ionosphere consists of some ions which influence radio waves. This is because, ionosphere is electrically charged with free electrons that allow the passage of radio waves, television waves and telephone or mobile phone waves.

V) Exosphere

Exosphere is the outermost layer of the Earth’s atmosphere, located above the thermosphere. It is the region where the atmosphere gradually thins out and merges into outer space, and gases such as hydrogen and helium can escape into space.

Function of Atmosphere

1. Insulation Atmosphere is an insulator

It acts as a shield or blanket and therefore regulates temperature during the night and during the winter.

2. Filtration.

The atmosphere is the filter, it filters solar insulation and percent ultra violet rays of certain length due to the presence of ozone layer in the stratosphere.

3. Scientific function.

Atmosphere is the scientific field, it is the field through which the scientific experiments and observation carried out. Example ionosphere layer of atmosphere reflects some electromagnetic waves and ration signals back to the earth.

4. It supports much on hydrological cycle.

The surface water, evaporation, condensation and precipitation formation take place in the atmosphere.

2. THE HYDROSPHERE

Is the layer of water bodies of the earth including all oceans, rivers, precipitation and underground water. It is estimated that 75% of the Earth’s surface is covered by water bodies.

3. THE LITHOSPHERE / LAND MASS

Is the whole solid body of the earth with various landforms such as mountains, valleys and plateaus. The lithosphere is also known as the crust. It includes all land masses.

The major land mass is called continent and the minor land mass is called islands.

4. THE BIOSPHERE

Biosphere is the complex zone which comprises all living things. It includes a lower level of atmosphere and the upper level of lithosphere and hydrosphere. Biosphere receives substantial supply of energy from the sun which gives it condition necessary for life and does not occur in any part of the solar system.

The living organisms that inhibit biosphere interact with each other and their environment. The sum of all these interaction components is called the ecological system or ecosystem. Biosphere comprises all living organism both macro and micro organisms living in water bodies, soils and on air.

WEATHERING

Weathering refers to a processes where by rocks disintegrate into small particles due to the agents of weathering such as water, ice, wind, wave, etc. The process results from the forces of weather, that is, changes in temperature, frost action and rain action.

Types of Weathering

The main forms of weathering include:

1. Mechanical weathering;
2. Chemical weathering; and
3. Biological weathering.

1. MECHANICAL WEATHERING/PHYSICAL WEATHERING

This is also referred to as physical weathering. It is a type of weathering caused by changes in temperature. It is common in areas where there are extreme changes in temperature such as hot deserts, arid and semi arid regions. Mechanical weathering includes the following types:

1. Exfoliation

The peeling-off the outer most layer. This process occurs due to temperature change. During the day time rocks expand due to high temperatures and contract during the night due to low temperatures.

Alternate heating and cooling set up powerful internal stress in the top layer of the rocks. The stress produces fractures which cause the outer layer to pull away leading to the cracking and disintegration of rocks into small particles.

The rocks that remain standing as exfoliation takes place are called exfoliation domes. Exfoliation domes occur in desert, semi-desert and monsoon regions. There are many exfoliation domes in the Egyptian, Kalahari, Sahara and Sinai deserts.

Exfolation

2. Granular Disintegration.

It is the breaking up the rock which consists of different minerals. These minerals expand and contract separately through temperature changes.

Granular Disintegration

3. Block Disintegration.

This takes place when the rock with homogeneous rock breaks into rectangular blocks due to changes in temperature. This is common when the rock is jointed . this process can be aided by chemical weathering.

4. Frost action

This is common in temperate regions where temperature falls up to freezing point. When temperature falls (freezing point) water collects in the rocks and it freezes, its volume increases causing the crack to deepen and widen.

Usually it involves the freezing of water in the cracks during the night and thawing (melting) during the day in mountainous areas. This action of thawing (melting) and freezing of water in the cracks cause the rocks to shatter (break) into angular fragments.

2. CHEMICAL WEATHERING

Chemical weathering involves the decomposition of some of the minerals contained in a rock. Some rocks decompose when they come into contact with water (H₂O), or oxygen (O₂) and carbon dioxide (CO₂), two of the gases that make up air.

Chemical weathering includes the following processes:

1. Oxidation

This happens when oxygen combines with a mineral. It takes place actively in rocks containing iron, when oxygen combines with iron to form iron oxides. This process is often preceded and accompanied by hydrolysis. The new minerals formed by oxidation are often easily attacked by other weathering processes.

2. Carbonation

This process occurs when hydrogen carbonate ions react with a mineral to give a soluble compound which can be carried away in solution. Hydrolysis often accompanies carbonation.

3. Solution

This refers to dissolution of a mineral with a chemical substance. Rain water combines with both atmospheric carbon dioxide and oxygen to form weak carbonic acid. CO₂(g) + H₂O(l) → H₂CO₃(aq).So when the rain reaches the ground it consists of a weak acid called weak carbonic acid. This acid helps to dissolve many insoluble minerals into minerals soluble in water, and which can be carried away in solution.

4. Hydration

This is the process in which some minerals absorb water and swell up, causing internal stress and fracture of the rocks.

5. Hydrolysis

This process involves the reaction of hydrogen (in the water) with certain mineral ions (in a mineral). This gives rise to the formation of different chemical compounds that can be easily weathered through other weathering processes.

3. BIOLOGICAL WEATHERING

When plants grow on rocks, their roots penetrate into rock joints which later force the rocks to break apart. Also man contributes much to rock disintegration through farming activities, mining, quarrying and construction.

Macro- and microorganisms also disintegrate rocks through burrowing and by mineralization process. Bacteria, for example, in the presence of air, break some minerals which are dissolved in the soil. Plants also absorb minerals from the soil by their roots. Decayed vegetation produce organic acid which remain in the soil. All of these actions help to weaken the rocks.

 

Disintegration of Rocks caused by Plants

Factors Which Control the Rates of Weathering

1. Rock composition

There are certain elements which are included in rock composition. Some rocks will weather quickly and some slowly e.g. acidic rocks weather more quickly than basic ones.

2. Climate

It includes the meteorological elements effect on rocks such as moisture, temperature, and wind and air pressure. Climate determines whether physical or chemical weathering will be more active and speedy.

3. Topography

Topography directly effects weathering by exposing rocks to the temperature or sun and wind. The elevated areas will be affected more and low level areas will be affected less.

4. Vegetation

Surface covered by the vegetation are protected from weathering but bare surfaces are weathered to great extent. – Thin root plants protects weathering – Thick root plants accelerates weathering

5. Length of Exposure: The longer a rock is exposed to the agents of weathering, the greater the degree of alteration, dissolution and physical breakup. Lava flows that are quickly buried by subsequent lava flows are less likely to be weathered than a flow which remains exposed to the elements for long periods of time.

The Significance of Weathering

1. Weathering leads to soil formation.
2. Tourism attraction.
3. The process helps to shape the earth and produce various landforms.
4. Help to get different minerals like Gold
5. Weathering serves as carbon sink. Any process that reduces the amount of carbon dioxide from the atmosphere is termed as carbon sink. Some processes of weathering involve absorption of carbon dioxide from the atmosphere. This helps to remove excess carbon dioxide from the atmosphere. Limestone and othercarbon-based sedimentary rocks are important carbon sinks.

MASS WASTING

Mass wasting is the movement of the weathered materials downslope due to gravitational forces accompanied by rain action. Mass wasting also known as slope movement or mass movement

Types of Mass Wasting

Types of mass movement are distinguished based on how the soil, regolith or rock moves down the slope as a whole. Based on this factor, mass wasting can be categorized or grouped into two types. These are:

1. Slow Movement
2. Rapid Movemen,

1. SLOW MASS MOVEMENT

This is the movement of soil at very slow speed, water acting as the lubricant. Slow mass wasting is categorized into several types. These are as follows:

1. Soil Creep

Soil creep is the slow movement of the soil downhill after it gets soaked by water. This process is very slow and its evidence is provided by tilting of trees and falling of buildings and fences. Soil creep is activated by any process that loosens the soil, making it easy to move gradually down the slope.

Factors Influence Soil Creep

• Alternate heating and cooling of the soil particles.
• The freezing of water in the soil causing frost heaving.
• Removal of the soil further down the slope.
• Percolation of water into the soil, acting as a lubricant.
• Ploughing of the soil, a fact which makes the soil loose and more mobile.

2. Talus Creep

It takes place due to the processes of thawing and freezing and is more pronounced in high latitude regions. It is very common on sides of mountains, scarps and valleys.

This is also a very slow mass movement of screes. Rock creep It occurs commonly where individual rock blocks are lying over clay materials. In the presence of moisture, the clay surface becomes slightly slippery.

The rock blocks may creep slowly down the slope under the influence of gravity. Individual rock blocks may move very slowly down a slope.

3. Solifluction.

This is the slow movement or flowing of weathered materials, especially when mixed with water and gravels. It is limited on highlands and cold regions.

 

2. RAPID MASS WASTING

This involves the movement of materials in form of mud flow, land slide, rock fall and earth flow.

a) Earth Flow

This type of movement occurs in humid regions. The materials on the earth’s surface gets so saturated with water that it gains much weight, and starts to move down the slope under the influence of gravity.

This normally occurs on the slopes of the hills or mountains. The removed earth material leaves a shallow scar on its place of origin and it creates terraces or mounds in its destination.

(B) Mudflow

Mudflow is the movement of a large mass of unconsolidated rocks down the slope when saturated with water. It flows in semi liquid state. It is common in desert slopes, which are not protected by a cover of vegetation. This occurs, for instance, during a torrential storm when more rain falls than the soil can absorb.

(c) Avalanches

It is a sudden and catastrophic movement of a wide variety of materials down slope associated with snow. The movement can take a flow or sliding or falling form.

(d) Land Slide

This is the rapid movement of surface rocks and soil down a steep slope such as a cliff face. It includes slumping and sliding of materials. During the movement, the block tilts and leaves holes.

It is common in well jointed limestone rocks, shale or clays. The common forms of landslides are slump, debris slide, rock slide, rock fall, debris fall and avalanche.

(e) Rock Fall

This is the free-falling of a single mass of rock, common on steep slopes of mountains and along scarp slopes of the sea. This is the most rapid of all mass movements. If a rock fall occurs repeatedly, for a long time, the broken rocks collect at the bottom of the slope in a mound called talus.

The Factors which Cause Mass Wasting

Mass wasting is caused by a number of factors which include the following:

1. Gradient or slope

When the gravitational force acting on a slope exceeds its resisting force, slope failure (mass wasting) occurs. Mass wasting is very common and severe in areas with steep lands as compared to flat or moderately flat lands.

2. Weathering

Weathering processes weaken and loosen the rock, hence accelerating the process of mass wasting. For example, oxidation of metallic elements and hydration of the minerals in rocks create lines of fracture and, consequently, the onset of mass wasting.

3. Amount of water present in the rocks

Water can increase or decrease the stability of a slope depending on the amount present. Small amounts of water can strengthen soils because the surface tension of water increases soil cohesion. This allows the soil to resist erosion better than if it were dry.

4. Vegetation

The roots of plants help bind the soil particles together making the soil resistant to agents of erosion and weathering. This makes the soil hard to break and hence resistant. Mass wasting processes, such as soil creep, cannot occur easily in soils well-covered with vegetation.

5. The nature or type of the rock materials

Clay soil is compact and resistant to various types of soil erosion agents and mass wasting as compared to sandy soil, which is normally loose and easy to remove and transport by water, gravity, wind, etc. Thus, mass wasting may be more severe on sandy soil than its counterpart clay soil under similar prevailing conditions.

6. Overloading

When the soil accumulates in one location as a heavy mass of the rock material, it can be moved either by action of gravitational force or application of just a little force. Landslides occur as a result of the soil accumulated on a sloping land to an extent of exceeding the resistant force of gravity. Movement occurs when the gravitational force exceeds the resistant force of soil material.

7. Earthquakes

Earthquakes cause sections of the mountains and hills to break off and slide down. Earthquake tremors tend to loosen the soil material and make it easy to be removed and transported. It can accelerate rock falls, landslides and soil creeps.

8. Human activities

The activities of man such as cultivation, burning, mining, transportation, animal grazing, etc, removes the soil cover or leads to shaking of the soil.

9. Climate

Climate has a great influence on mass wasting. Areas that receive heavy rains often experience mass movements, such as landslides and soil creep, more often compared to dry areas. On the other hand, a little amount of rainfall does not wet the soil and so cannot cause the soil to move. In cold regions, alternate freezing and thawing triggers mass wasting.

10. Vulcanicity

Volcanic activity often causes huge mudflows when the icy cover of a volcano melts and mixes with the soil to form mud as the magma in the volcano stirs preceding an eruption.

The Effects of Mass Wasting to the Environment

1. Formation of fertile land
2. Tourism attraction
3. Formation of new landforms
4. Formation of lakes:
5. Diversion of a river course
6. land degradation
7. Damage to property and Loss of life: The more populations expand and occupy more and more of the land surface, mass movement processes become more likely to affect humans.

RIVER AND RIVER SYSTEMS

River refers to a mass of water flowing through a definite channel over a landscape from river source to river mouth. River source is the place where a river starts. It may be in the melt water from glacier e.g. river Rhome (France), a lake, e.g.

Lake Victoria, the source of river Nile, a spring e.g. Thames (England) or it can be formed following steady rainfall e.g. river Congo. River mouth can be anywhere a river pours its water, e.g. a lake, ocean or sea.

Running water

Running water refers to water flowing over the Earth’s surface, such as in rivers, streams, and surface runoff, which acts as an important agent of erosion, transportation, and deposition. The runoffs form three types of erosion: sheet erosion, rill erosion and gully erosion.

1. Sheet erosion

Sheet erosion is the uniform removal of a thin layer of topsoil over a wide area by running water, usually after heavy rainfall, without forming visible channels.

2. Rill erosion

Rill erosion is the formation of small, shallow channels on the soil surface caused by running water, especially on sloping land.

3. Gully erosion

Gully erosion is an advanced stage of erosion where large, deep channels (gullies) are formed by running water, which cannot be easily removed by normal cultivation.

How Agents of Erosion and Deposition Operate on the Landscape

The river has three functions as it flows through its channel. These are river erosion, transportation and deposition.

1. RIVER EROSION

Erosion of a river operates in three ways: head ward, vertical and lateral erosions.

Head ward erosion – this is the cutting back of the river at its source. It is through this erosion that a river increases its length.

Vertical erosion – this is erosion by which a river deepens its channel.

Lateral erosion – This is the wearing away of the sides of a river by water and its load. It is responsible for widening of a river valley.

River erosion involves four related processes. These are abrasion (corrasion), attrition, corrosion (solution) and hydraulic action.

Hydraulic Action:This is the process whereby the force of moving water plucks and sweeps away loose materials, such as silt, gravel and pebbles. Materials plucked by hydraulic action are responsible for bank caving and slumping.

Corrasion (abrasion): This is when the load of the river rubs against the bed and sides of the river channel. This causes wearing away of the sides and bed of the river. The amount of load determines the nature of erosive power and rate of erosion. This is a source of pot holes in the river bed.

Attrition: This is when the rock fragments in a river’s load are broken into small fragments due to collision against one another as the load is carried downstream along the river channel. As the river moves along its course, its fragments get progressively smaller because of disintegration and wearing away.

Corrosion (solution): River water dissolves certain minerals leading to dissolution and disappearance of some rocks, e.g. limestone, rock salt and chalk.

2. RIVER TRANSPORT

This is the process which involves carrying away of the weathered and eroded, loose materials from one place to another. The materials carried out by river is called load.

River transports its load in four ways:

Saltation – this is the process in which small pieces of the rock fragments are carried by a river while bouncing on the river bed.

Traction – this is the dragging or rolling of large boulder such as pebbles along its river bed.

Suspension – This involves transport of fine or light materials like silt and mud, which are carried in suspension forms. This is common when the river flow is too strong.

Solution – this involves moving some materials that dissolve in water, which are carried away in solution form. A river transports its load until it has insufficient energy to transport it any further.When this happens, the load is deposited.

3. RIVER DEPOSITION

A river deposits its load when its volume and speed decrease.

a) A river volume decreases when:

• It enters an arid region especially a hot desert;
• it crosses a region composed of a porous rocks e.g. sand and limestone; and
• During the dry seasons or in a period of drought.

b) A river speed decreases when:

• it enters a lake or sea; or
• when it enters flat or gently slopping plain such as a valley bottom.

Deposition takes place when the river has insufficient energy to carry its entire load. The first part of the load that is dropped consists of boulders and pebbles. The last part to be dropped is the fine sediment, called silt. Deposition takes place at any point in a river’s course.

THE LONG PROFILE OF A RIVER

The long profile of a river is the line following the course of a river from its source to its mouth. Three courses or sections of a river can be distinguished.

These are:

1. The upper course.
2. The middle course.
3. The lower course.

Long Profile of the River

1. THE UPPER COURSE

This is the first stage of a river. It is sometimes called the youth or torrent course.

Its characteristics are as follows:

1. It is the river source.
2. The speed of a river is high.
3. Most of the works of the river include vertical erosion.
4. The cross-section of a river valley in this section of a river is V–shaped.
5. The slope of a profile is very steep.
6. It is sometimes utilized for hydroelectric power (H.E.P) generation. Erosional and

Features produced in the upper course of a river

The main features of the upper section are deep and narrow, V-shaped valley; a steep gradient; pot holes on the river bed; interlocking spurs and waterfalls and rapids, often with plunge pools.

1. V–shaped valley

This is a deep, narrow valley at youth/first stage of a river.

2. Pot holes

These are circular depressions on the river bed. They are formed when pebbles carried by the swirling water cut circular depressions in the river’s bed.

3. Interlocking spurs

An interlocking spur, also known as an overlapping spur, is one of any of a number of projecting ridges that extend alternately from the opposite sides of the wall of a young, V-shaped valley down which a river with a winding course flows.

Interlocking spurs

4. Waterfall

A waterfall is a place where water flows over a vertical drop in the course of a stream or river. A waterfall is formed when there is sudden change or drop in the bed of a river.

Although waterfalls can occur in almost any part of a river’s course, they are most common in the upper course. Examples of waterfalls are Owen Falls in Uganda, Victoria Falls in Zimbabwe and The Livingstone

5. Rapids

These are sections of a river where the river bed has a relatively steep gradient, causing an increase in water velocity and turbulence. Rapids are characterised by the river becoming shallower with some rocks exposed above the flow surface.

6. Plunge Pool: This is a large depression formed at the base of a waterfall.

7. Gorge: It is a steep, narrow and elongated valley. A gorge often is formed when a waterfall retreats upstream, e.g. a gorge found in Victoria Falls.CANYON- Is the widened , deep gorge.

2. THE MIDDLE / MATURITY STAGE

This is the second stage of a river. The main features of this section are bluffs and waterfalls and rapids.

The Characteristics Features of the Middle Course of a River Valley

1. The speed of a river is fairly low.
2. Most of the work of a river is transportation.
3. The cross–section of a valley in this section is an open V.
4. The slope of a relief is gentle
5. The volume of a river increases.
6. Lateral erosion predominates.

Middle Course of the River

Features Associated with the Middle course of a River Valley

1. Bluffs: These are steep slopes of the truncated spurs in middle course where interlocking spurs turn into bluffs.
2. Waterfalls and rapids: Waterfalls and rapids can also be found in the middle stage of the river valley. This is mainly caused by river rejuvenation which increases erosive activity and transportation, hence development of waterfalls.

3. THE OLD / LOWER STAGE

Third is the third stage of a river. The main features of the lower section of a river valley are a flood plain; braided river; ox-bow lake; levee and deferred tributary and delta.

Characteristics of Lower Stage

1. It is the river mouth.
2. Always there are gradient falls or slope falls.
3. The main work of a river is deposition.
4. The cross–section of a valley is a U–shaped valley.
5. The speed of a river is decreased.
6. The river valley is very wide.

Lower Course of the River

The Importance of Erosional and Depositional Features to Human Beings

1. Loess form very fertile soil in desert land,
2. Water falls attract tourists; headlands in coastal areas are natural ports.
3. Coastal features form breeding places for fish,
4. Coral reefs are used as building materials and for settlement.

RIVER CAPTURE (RIVER PIRACY)

River capture, also known as river piracy, is the process by which one river captures the headwaters of another river due to stronger erosional power, causing the captured river to lose part of its water.

Conditions Necessary for River Capture

1. The capturing river must have strong energy for vertical and headward erosion.
2. The capturing river must lie at a lower level and have a steeper gradient than the neighbouring river.
3. The two rivers must be in the same catchment (drainage basin).
4. The two rivers must be close to each other and separated by a narrow watershed or divide.

Features resulting from a river River Capture

a) Pirate Stream

The pirate stream is the river that captures the headwaters of another river and gains more water and energy.

b) Elbow of Capture

The elbow of capture is a sharp bend formed where the captured river suddenly changes direction.

c) Misfit River

A misfit river is a small river flowing in a large valley, showing that a bigger river once flowed there.

d) Wind Gap

A wind gap is a dry or abandoned valley left after river capture has taken place.

River Rejuvenation

River rejuvenation is the renewal of the erosive power of a river, usually caused by a fall in base level, uplift of land, or an increase in the volume of water, which makes the river start vertical erosion again.

Features of River Rejuvenation

a. Knick points

Knick points are sudden breaks or steep steps in the river’s long profile formed due to the renewed vertical erosion of a rejuvenated river. They may appear as waterfalls or rapids.

B. Paired Terraces

Paired terraces are step-like flat surfaces found on both sides of a river valley. They are formed when renewed erosion causes the river to cut downwards, leaving the former floodplain at a higher level.

C. Incised Meanders

Incised meanders are deeply cut meandering bends formed when the renewed erosive power of the river causes it to erode vertically while maintaining its original meandering pattern.

River Regime

River regime is the seasonal variation in the volume of water (discharge) of a river throughout the year, depending on its source of water supply.

Types of River Regime

a) Simple River Regime

A simple river regime is one in which a river is fed by only one main source of water, such as rainfall, snow, or glaciers. The river shows one clear maximum and one minimum flow in a year.

b) Double River Regime

A double river regime occurs when a river is fed by two different sources of water, for example rainfall and melting snow. The river shows two periods of high discharge in a year.

c) Complex River Regime

A complex river regime is found in rivers fed by more than two sources of water, such as rainfall, snow, and glaciers. The river shows irregular or multiple peaks of discharge throughout the year.

Importance of River Regime

Helps in planning irrigation and farming activities.

Help in flood prediction and control.

Useful for hydroelectric power generation.

Helps in effective water resource management.

Indicates climatic conditions and seasonal changes in a region.

Facilitates construction and management of dams and irrigation schemes.

Guides planning and development of settlements and towns that depend on river water.

Negative impacts of river

If can cause deseases such as chorela and bilharzra

It is a habitat to dangeraous animals

Can cause floods during heavy rainfall

Underground Water in Karst Region

Underground water in a Karst region is the water that flows or is stored beneath the surface in areas underlain by soluble rocks (mainly limestone). It dissolves the rocks through chemical weathering, forming caves, underground rivers, and other Karst features.

Features of Karst Region

1. Surface Features

a) Sinkhole

A circular depression on the ground surface formed by the collapse of an underground cave roof or by dissolution of limestone.

b) Doline

A small or large depression on the Karst surface caused by chemical weathering and collapse.

c) Uvala

A large, elongated depression formed when several sinkholes merge. It is larger than a single doline.

d) Polje

A very large flat-floored depression, often several kilometers long, formed by merging of many dolines and uvalas. It may occasionally be flooded.

2. Underground Features

a) Natural Pillar (Column)

A pillar of limestone formed when a stalactite (from the roof) and a stalagmite (from the floor) meet and join.

b) Stalagmite

A cone-shaped deposit of calcium carbonate rising from the floor of a cave, formed by dripping water.

c) Stalactite

A hanging deposit of calcium carbonate from the roof of a cave, formed by dripping water.

d) Cave

A natural underground hollow or chamber formed by dissolution of limestone by underground water.

WIND ACTION IN THE DESERT

Wind action is also known as Aeolian. It causes erosion transportation and deposition of materials in the desert.

WIND EROSION

Refers to the remove of particles on the desert surface. Wind erosion consists of three main processes.

These are

Deflation

Is the process by which small the wind blows away loose rock waste and in doing so lowers desert surfaces producing deflation.

Abrasion

Is the process by which small particles of rock are hurled by wind against the rock surfaces helping to produce features like rock pedestals, Zeugen and Yardangs. During abrasion, the wind exerts the blessing action and uses its load as the tool for polishing and undercutting the surface.

Attrition

Is the process by which the rock particles rule or collide against each other as they carried along with wind. The particles get progressively reduced in size through this way until they become finer and finer.

WIND EROSIONAL FEATURES

The desert wind erosional features include the following

1. Rock pedestals

Are the tower like structures composed of alterate bands of soft and hard rock produced due to wind abrasion in the desert. As abrasion goes on attacking the weaker rock, the pedestal may break at the base and collapse.

There are rock pedestals in Saudi Arabia, Tibest Mountains in central Sahara and in Niger.

ii. Zeugen

Are the ridge consisted of alternate layers of hard and soft rock overlying vertically downward.

• They are formed in areas where the rock layers lie horizontally and are characterized by joints.
• The weathering process first opens up the joints and then wind abrasion continues the work of weathering leading to the formation of furrows and Zeugen

iii. Yardangs

Are the ridges consisted of hard and resistant rock bands standing either vertically or at an angle and can vary in height from 5m to 15m but having lengths of up to 1000m.

The yardangs are parallel to the direction of the prevailing wind. Example: – Yardangs can found near Salah (central Algeria and near Kom Ombo in Egypt.

iv. Deflation hollows or pans.

These are the hollows or depressions produced by wind deflation.

• The small hollows are known as pans and are common in Kalahari Desert.
• Larger hollows like Qattara Depression in Egypt were formed by wind deflation.
• When these hollows are filled with water OASIS are formed.
• OASIS means a fertile area in a desert where water is available.

It is usually formed where underground water reaches the surface, allowing plants, trees, animals, and people to live there.

v. Inselbergs

 

 

• Are the residual hills consisted of hard and resistant rock left standing on the surface after the rest part of the earth has been eroded
• When inselbergs are smooth and round in shape are called bornardts
• When the inselbergs are characterized by a lot of joints with rectangular rock blocks pilled together to produce a castellated form are called Kopjes

Note: – Inselbergs investigated that, many of them in the desert are formed due to the water action rather than wind action.

vi. Ventifacts

Are heavier rock blocks or pebbles left behind after the wind has sorted and carried away all material.

– They are sharpened and flattened as they lie by the action at the sandblast passing over them

WIND ACTION DEPOSITIONAL FEATURES

The material transported by wind from different features after deposition. The features formed include the following

• Sand Dunes

Are the hills of sand which have been deposited by winds in the desert

The formation of sand dunes is influenced by the extent of vegetation cover, the size of particles amount of the material and velocity of the wind.

There are two main types of sand dunes.

These are

1. Barchans
2. Seifs

BARCHANS / BARKHANS

Are the crescents – shaped sand dunes which occur individually or in groups.

• Development of barchans is usually influenced by the obstruction which may be a tree or large stone.
• The windward side of the barchans is steep and slightly concave.

SEIF DUNES

• Seif dunes are also known as longitudinal dunes.
• They are long narrow ridge of sand which lies parallel to the direction of the wind.
• They usually occur on the small scale in sandy areas such as along the coasts and in the extensive sides of the river valley but such sand dunes are in small size because of the limited supply of sand.

LOESS

Is the accumulation of the fine particles of sand that have been carried beyond the limit of deserts.

• They are mostly found in loess plateaus of the China.
• The loess leads to the formation of fertile soil

WATER EROSIONAL FEATURES IN DESERT

Desert Landforms Formed by Water Erosion

1. Pediment

A gently sloping rocky surface at the base of mountains, formed by sheet wash and weathering during rare desert rains. It often extends from the mountain base into the plain.

2. Butte

A steep-sided, isolated hill rising abruptly from the plain, smaller than a mesa. It forms when hard rock resists erosion while surrounding softer rocks are worn away.

3. Mesa

A flat-topped, steep-sided hill larger than a butte. Mesas are remnants of plateaus eroded by water and wind, with resistant cap rock protecting softer layers beneath.

4. Wadi

A dry riverbed or valley that carries water only during heavy rains. Wadis are common in deserts and are formed by intermittent water flow.

5. Gully

A small, narrow channel cut into the soil or soft rock by running water, usually during rare but intense desert rains.

6. Valley

A long, low area between hills or mountains, often with a stream or river (permanent or seasonal) flowing through it. Desert valleys are mainly formed by water erosion during flash floods.

7. Oasis

A fertile area in a desert where underground water reaches the surface, supporting vegetation and human settlement. Often formed at natural depressions where water accumulates.

COASTAL LANDFORMS

A coast is a land or area near the ocean or sea. Coastal zone or line is a part of the coastal land bordering the sea or the part which can be reached by the strongest sea waves. The term is related to the study of the coast.

Definition of terms

Swash: This is the forward movement of waves from the coastline.

Backwash: This is the backward movement of waves from the coastline.

Wave: The upward and downward movement of water following the direction of wind.\

Crest: The highest apart of the wave.

Trough: The lowest part of the wave.

Wavelength: The distance from crest to crest or trough to trough.

Wave height (pitch): The distance between the crest the trough. The size of the wave or wave or wavelength depends on the strength of the wind, i.e. the stronger the wind the larger the waves and wavelength, and vice versa.

The coast has various physical features often termed as coastal landforms. These features have been formed due to various factors or changes (natural and manmade) which have affected the coastline or coastal zone. There are different factors for the changes or evolution in the coastline (the factors influencing the development of a coastline).

The factors are divided into two groups:

a) Natural factors

1. This includes the work of ocean waves, currents and tides and agents of erosion, transportation and deposition. For example, the coastline may be affected by marine (wave erosional process forming such features such as cliffs, sea caves, wave-cut platforms, etc) and by marine (wave) deposition forming such features as beach, spit, sand bars etc.

2. The nature of the coastal rocks, i.e. Whether the coastal rocks are resistance to wave erosion or weathering or not. Where the coastal is resistant to marine erosion and weathering, coastal cliffs and headlands may be formed. Where the coastal rocks are not resistant to marine erosion and weathering, bays and caves will be formed..

3. The effects of glacier and ice sheets reaching the sea or ocean. These may increase the sea or ocean level and hence lead to the submergence of the coastal areas forming landforms such as fiords (Fjords), and Rias.

4. Volcanic eruption and earthquakes along the coast. These may from various volcanic coastal features or may cause displacement or faulting of the coastal rocks.

Growth of reefs along the eastern coasts of Tropical Ocean water, e.g. fringing reef, barrier reef, atoll, etc.

b) Man-made factors

1. Through engineering activities such as construction of ports and dredging of estuaries.

2. Through land reclamations processes of agriculture, settlements or recreation

3. Through construction of dykes and lifeguard towers.

4. Through quarrying activities along the coast e.g. quarrying of sand and gravels.

5. Mining along the coast.

6. Fishing by using illegal means such as dynamites or explosives. Marine (wave) erosion refers to the coast by waves (current and tides). Processes involved in marine erosion (marine erosion process) are

Marine (wave) erosional features (land forms)

Cliff: This is rough, steep sided coastal rock facing the sea or ocean. It may be formed due to marine abrasion.

Wave-cut platform

A wave-cut platform is a gently sloping, flat rocky surface found at the base of a cliff. It is formed when waves erode the foot of the cliff through hydraulic action and abrasion, causing the cliff to collapse and retreat inland.

Cave and Ledges

A cave is a hollow or opening formed at the base of a cliff when waves exploit lines of weakness such as joints or faults in the rock through continuous erosion. Ledges are narrow, step-like rocky surfaces found on the face or at the base of a cliff. They are formed when waves erode softer rock layers faster than harder layers.

Blowhole

A blowhole is a vertical hole that connects the roof of a sea cave to the land surface above. It is formed when wave pressure forces air and water through cracks, eventually breaking through the roof.

Geo

A geo is a narrow, steep-sided inlet formed when waves enlarge a crack or cave in a cliff until it penetrates deeply inland.

Arch

An arch is a natural curved opening through a headland. It forms when waves erode a cave on both sides of a headland until the caves meet.

Stack

A stack is an isolated pillar of rock standing in the sea near the coast. It is formed when the roof of an arch collapses due to continued wave erosion.

Stump

A stump is a short, low remnant of a stack that has been further eroded by waves and is often visible only at low tide.

Bay

A wide, curved inlet of the sea where the land bends inward.

FEATURES PRODUCED BY WAVE DEPOSITION

Beach: This refers to a deposit of mud, sand or pebble on the sea store. A beach has a gently sloping surface, usually formed between low water and high water levels.

Spit: Spite is a low, narrow ridge of pebbles or sand joined to the land (mainland or island) at one end, with the other end terminating in sea. It is formed by deposition of material by long shore drift.

Sand Bar: The words spit and bar are often confused and misused. A bar is a ridge of material, usually sand, which lies parallel, or almost parallel, to the coast. Unlike a spit, a bar is not attached to the land.

Tombolo: This is a bar that joins an island to the mainland.

Mudflat: This refers to fine silt deposited along gently sloping coasts, especially in bays and estuaries. This deposition of silt, together perhaps with river alluvium, results in the building of a platform of mud called mudflat.

CORAL REEF

A coral reef is a large underwater structure made mainly of skeletons of tiny marine animals called coral polyps. These polyps live in colonies and secrete calcium carbonate (limestone), which builds up over time to form massive reef structures. Coral reefs are sometimes called “the rain forests of the sea” because they support a huge variety of marine life.

Types of Coral Reefs

1. Fringing Reefs

Found close to the shore, attached directly to the coastline. o Separated from the land only by a shallow lagoon or no lagoon at all.

Example: Reefs along the coast of East Africa (Kenya, Tanzania).

2. Barrier Reefs

Lie farther away from the shore and are separated from the mainland by a deep, wide lagoon.

They run parallel to the coastline. o Example: The Great Barrier Reef in Australia (largest in the world).

3. Atoll reef

Ring-shaped reefs that surround a central lagoon but have no land in the middle.

Usually form on submerged volcanic islands.

Example: Maldives, Bikini Atoll (Pacific Ocean).

 

CONDITIONS NECESSARY FOR CORAL REEF FORMATION

Warm Water Temperature o Coral reefs grow best in warm seas, usually between 20°C – 30°C.

Shallow Water Depth o Reefs require shallow waters (not deeper than 50–70 meters) so that sunlight can penetrate.

Clear Water o Water must be clear and free from mud, silt, or pollutants, because corals need sunlight for photosynthesis (through symbiotic algae called zooxanthellae).

Abundant Sunlight o Essential for photosynthesis; reefs grow in areas with plenty of sunshine.

Salty (Marine) Water o Corals need saline ocean water, usually between 27–40 parts per thousand (ppt).

Stable Substrate o A solid, hard surface such as submerged rocks or old coral remains is necessary for coral larvae to attach and grow.

Oxygenated Water and Ocean Currents o Steady wave action or currents provide oxygen, nutrients, and prevent the buildup of sediments on corals.

VALUES/ADVANTAGES/ SIGNIFICANCE/ IMPORTANCE OF CORAL REEFS

They used for decoration.

They are used as raw materials in the manufacturing of cement and gypsum powder.

They are used as raw materials in pharmaceutical industries for example the production of plaster of Paris (P.O.P).

Provide habitats for sea turtles, algae, and fish.

They provide good fish breeding grounds.

Coastal Protection from erosion, flooding and storm damage. Reefs act as natural barriers, protecting shorelines from erosion, strong waves, storms, and even tsunamis.

Tourism and Recreation. Coral reefs attract tourists for snorkeling, diving, and beach holidays, generating income and supporting local economies.

Cultural and Spiritual Value. Many coastal communities consider reefs sacred and part of their cultural heritage.

DISADVANTAGES OF CORAL REEFS

They hinder the development or occurrence of natural harbours.

They are barrier to navigation.

They block waves hence it hinder the development of beach and other features

It a habitat for dangerous animals like crocodile

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