The Dynamic-Earth And Consequence

EARTHQUAKES

Is the shaking of the ground due to the sudden vibrations.

Are vibrations of the earth crust caused by volcanic eruptions.

Sudden vibration of the earth caused by rupture and sudden movements of rocks that have been strained beyond their elastic limit.

It takes a short time, hardly reaches 5 minutes.

Causes of earth quakes;

1} Diastrophic movement

Movement of plates one tectonic plate sliding over or past another plate

2} Volcanism

Intrusion between crustal rocks can cause sudden vibrations intrusion or extraction causes vibration

3} Human activities

E.g. explosion of bombs for example atomic nuclear bombs which can cause shaking in a very large area.

A transportation large airplane trains.

Dynamites

Major causes are diastrophic movement:

This can be explained by the theory of elastic rebound.

There are compressions forces which make the crustal rocks bend.

The forces build up strain when the strain is so great it will result into breakage of the crustal rocks to release energy. The energy will cause seismic waves. The seismic waves will cause the shaking vibration of the earth.

The place where earth quake occurs /origin of earth quake the point where the breaking occurs is called focus.

This breakage only occurs in the solid part of the earth (earth crust) between 8-100km beneath the surface of the earth.

From the focus, seismic waves are sent to all directions and the point vertically above the focus is called epicenter (on the earth crust) point of the surface of the earth vertically above the focus .Epicenter refers to the point where the effect of the earth quake is the greatest

Types of seismic waves

Two main types of seismic waves;

i. Body waves

ii. Surface waves

ii. Body waves

Travel through the crust. There of two types

Primary (p) waves

These are compression waves. These can be transmitted through solids, liquid s and gasses. They are transmitted to all.

Can be pass on the center of the earth and be felt on the other

They are fastest can travel 8km/sec.

Crustal rocks move back and forth in the direction of wave movements

Secondary (s) waves

These are shear waves. These can only pass through solids. They are slower, when they reach the mantle there reflect (bend). They speed is 4km, sec.

The crustal rock to move from side to side perpendicular, at right angle to the direction of wave movement.

Produces shadow zone to the area which the secondary waves do not pass

ii. Surface waves

These travel through the surface rocks and are of two types,

a) Love (L)waves

b) Rayleigh (R)waves

Love (L)wave

Move from side to side at right angles to the direction of wave movement.

Ray Light ® waves

Have a vertical circular movement very similar to that of water in sea wave. They move

Up and down.

The energy moves form one point to the next.

THE STRUCTURE OF THE EARTH SHOWING THE PATHS OF EARTH QUAKE WAVES BASED
ON VARIOUS GEOPHYSICAL MEMOIRS.

MEASUREMENT OF SEISMIC WAVES

Magnitude: – The size of quake is measured on Richter scale (size of magnitude is measured on Richter scale) ranges 0 – 8.9

Total energy released which is transmitted to all direction is measured on Richter scale.

Intensity – The effect / damage experienced on the surface or on the ground / destruction. Measure on Mercalli scale which ranges from 1-12.

1 is the smallest effect detected by seismograph

12 is the most catastrophic effect.

Global distributions of earth quakes

MAP OF THE WORLD SHOWING THE ZONES OF E.Q

The majority of E.Q occurs in narrow belts which mark the boundaries of tectonic plates. The main types of regions where they occur are:

The mid-ocean ridges

The ocean deeps and volcanic islands

Regions of crustal compression

Major E.Q are caused by the movement of tectonic plates e.g. the North American and Pacific Plates result in Horizontal movements along San Andreas Fault in California.

The only parts of Africa which have E.Q are located in the Great Rift Valley Region of East Africa and in parts of North – West Africa. Most of the E.Q occurring in Africa is relatively mild. However, serious earthquakes occurred in El Asnam in 1954 and in Agadir in 1960.

THE MAJOR EARTH QUAKE AND VOLCANIC BELTS ON THE WORLD

Effects of Earth quakes

1. Destruction of life. For example in Iran, 20 thousand people died, In Morocco. Chile.

2. Destruction of property, breaking of buildings example in Morocco where building and transportation system collapse.

3. Can cause faulting / joints e.g. San Andreas in California.

4. Displacement of crustal rocks can be vertical or lateral. (Land can be uplifted) e.g. San Andreas.

5. Can cause land slide which can cause some blockage on transport system or rivers. Also open up deep cracks in the surface rocks eg. The El Asnam E.Q in Algeria.

6. Devastation especially in cities.

7. Tsunami. Great seismic waves which are caused on the ocean flow due to earth quakes.

Precautions against Earthquake

Natural disaster, how to reduce its negative impact.

1. Discourage settlement on those areas which are frequently prone to earth quake.

2. Run to open space

3. Build houses which are shock absolve.

4. Do not build tall buildings on areas prone to Earthquake.

5. Avoid using explosives especially exploding atomic bombs, nuclear bombs.

6. Seismologist(seismographers) should detect the Earthquake and inform the people

EXOGENETIC FORCES WHICH SCULPTURE THE SURFACE OF THE EARTH.

These are external forces. They operate on the surface of the earth.

Denudation:

These are destructive forces which lower the earth’s surface

Weathering / mass wasting

Erosion

Transportation

Deposition – Constructive process which raise the eland

VULCANICITY (VULCANISM)

Is a process whereby molten (magma) material from the interior of the earth is injected into between the crustal layers the earth crust rocks or ejected on the earth surface.

This material can be inform of gases where gaseous material or in liquid or solid.

Material which is injected between rock layers form intrusive igneous rock while that which is ejected out in the surface form extrusive igneous rock.

Intrusive magma form intrusive features of Vulcanism while extrusive magma form extrusive features of Volcanism (lava). The shape of the features form depends on the nature and weakness or strength of the bedrock.

VULCANICITY

Vulcanicity includes extrusive and intrusive while volcanicity is a subset / part of vulcanicity (surface manifestation of vulcanicity).

Causes of Volcanism

Intensive Pressure: –

This pressure is so high and it finds the line of weakness where it can come out. The line of weakness is found on the boundaries of tectonic plates. Pressure causes high temperature and hence it tends to release with molten material and this causes.

Intrusive features of vulcanism;

1. Dykes

2.Sill

3.Lacolith

4.Batholith

5.Lopolith

6.Phacolith

7.Minor features.

-The shape of the intrusive features depends on nature and strength or weakness of the bedrock.

Fluidity which is very fluid it will move very far and form linear features.

Thick, accumulate (viscous) and solidify and form features.

Dykes

Intrusion of magma which solidify vertically across bedding rock strata or can be inclined magma.

They are pillar like structures.

These dykes can be exposed by denudation. It depends if the rocks of the dyke is more resistance (harder) than the surrounding rocks, the surrounding rocks will be eroded and form a rigid.

And if the dyke is soften than the surround rock it will be eroded and form a depression.

Example: The dyke which give rise to waterfalls or rapids such as Howick falls on the River Mgeni in S.A, Dyke ridges on the S W side of the Kaap Valley S.A, West of Lake Turkana (Rudolf) where dyke form trenches in sedimentary Turkana grits.

Sill

Is a horizontal sheet of intrusive rocks where magma has solidified between rock layers / bedding layers.

The magma is very fluid and moves very far

If it cuts across a river, it can cause a water fall. Due to erosion the river erodes the surface but when crossing the dyke or sill the rocks are hard to erode but after crossing the rock it will erode faster and after many years will form H₂O fall.

Examples: In Cape Province of S.A are buttes which have a sill capping, Kinkon falls in Guinea.

Lacolith: is a dome shaped of intrusive magma (caused by accumulation of viscous magma which pushes the overlying rock layers to bend upward.

Laccoliths are near the surface

Examples: Fonjay massif and Ambereny massif in Madagascar, Henry Mountains in southern Utah to the west of the Colorado River.

Batholiths

Are very large masses of igneous rock which are formed deep in the crust (plutonic).

Examples are granites which are made up of large crystals because cooling has taken a very long time.

They normally form roots for mountains.

Batholiths’ can be exposed by denudation.

Examples: Granite batholiths in S.w peninsula of England and in beuttany,Tanzania batholith in Mwanza and Iringa,sinda batholith, East Zambia, Cape coast batholith in Ghana and Sinso batholiths in

Uganda.

Lopolith

They are saucer like feature formed by sagging.

Very large saucer shaped intrusion shape may be due to increased weight causing sinking. After denudation the upturned edges sometimes form out facing scarps.

Examples: the bushveld basin in the Transvaal in S.A, sierra lione peninsula.

Phacolith

These are intrusive solidification of magma on the anticlines and synclines of rock strata.

Extrusive features of volcanism:

Magma which reaches the surface is called lava

LAVA: Can come out in two ways;

Through fissure eruption/linear

Magma wells up and pours out into the surface through a crack or a whole (Explosion) quietly

Vent eruption: Magma is forced out through a vent or central opening violently.

Types of materials given out during eruption

Gaseous Materials – Gases are emitted during the course of an eruption include gaseous compound of sulphur, hydrogen, carbon dioxide.

Liquid – There is lava which can be mobile (flow faster) or viscous tephra (accumulate and flows).

– Acidic Lava

-Basic Lava

Solid – Solid materials are ejected, some are fragment of the country rock; e.g. Scoria, pumice, cinder (lapilli), volcanic bombs.

Those which come out explosively will spread out far. But will fall and cool and build landforms.

Some of these materials will cool and accumulate and build landforms. Those which come out slowly build up a volcano.

VOLCANO – Is a mould or a cone like features or a circular in shape build up through volcanic activity (is a result from volcanic activities)

Types of Volcano

Active Volcano Domant Volcano Extint Volcano

Volcanic Landforms

Ash and Cinder cone (scoria cones).

These cones are building up by pryroclastic material solidifying around the vent.

Formed by vent eruption cinder are small round particles either from the interior of the earth or have solidity after being exposed out of the crust. Examples: South of L. Turkana in Kenya, Likaiyu and Teleke (both under cinder cone) and Nabuyatom (ash cone)

The structure of an ash and cinder cone

Lava Cones

A hill or type of a cone which is formed by lava (cumulo dome)

Acidic Lava

This is viscous and will not flow very far from the vent but accumulates around the vent to form sleep sided cones. Viscous lava can form a spine (is a steep hill) has more silica.

Example: Mount Pelee Martinique West Indies.

Basic Lava Cone

Is very fluid, mobile. It spread far from the vent and it builds up gentle sloping cones.

Example: Mauna Loa – Hawaii.

Composite cone

This is formed by alternating layers of ash and lava

Note: These composite cones forms high composite peaks – (give highest peaks on the surface of the earth) e.g. Mountain Cameroon, Mount Kilimanjaro, Mount Vesuvius.

Iv. Plug Volcano (Volcanic neck) – They are cylinder like shaped it occupies the vent of a dormant or extinct volcano. It solidifies on the vest, and blocks the mountain forming dormant volcano.

Caldera (Basal Wreck)

Is a large shallow cavity (depression) on the top of the volcano.

How formed

Formed by violent eruptions which remove the former top of the volcano.

NB: Water can accumulate in the caldera and form Caldera lakes e.g. Lake Toba in Sumatra (Indonesia) and Crater Lake in USA and Bosumtwi in Ghana

Caldera; Ngorongoro in Tanzania, Mount Meru in Tanzania, Longonot in the Eastern Rift S.W of Kenya.

Stages in the formation of a caldera

Lava Plateau

Result from fissure eruption. When lava is up welled then spreads to a wide area and when it solidifies forms lava plateau. (fairly high level lava plateau) (Basalt plateau which is acidic in nature). E.g. In Sahara, Algeria, Morocco and in S.S – Drakensberg Plateau, North America

– Snake plateau, Deccan plateau in India.

Other minor features associated with volcanism.

a) Hot spring – Natural outflow of hot H₂O from the ground. E.g. In Mbeya, Arusha, Mara –

Majimoto.

FORMATION OF GEYSERS

Geysers – Superheated H₂O and steam is drawn out with great force and sometimes explosively in comes periodically.

Solfatara – Is a volcano which releases only steam and gas. The large % of gas is sulphur.

Fumaroles – Emission of steam

Mofatte– Emission of carbon dioxide.

Stages / life cycle of Volcano.

Active volcano – One which is definite / takes place periodically in recent time. Example oldonyo in Tanzania, Mufungiro in Uganda, Italy Vesuvius.

Dormant Volcano (sleeping) – Has erupted before but has stayed dormant for a long while and not sure if it will erupt again or not. E.g. Mount Kilimanjaro, Mount Meru, it has signs of eruption

Extinct (dead) Volcano – A volcano which has remained dormant and doesn’t have any signs

of eruption.

Global Distribution of Volcanoes and lava Plateau

Vulcanicity occurs in areas where the earth’s crust disturbed. These are the areas where weaknesses in the crustal rocks provide an easy passage for volcanic materials to escape into the earth’s crust or onto the surface of the earth. For this reason volcanic features and active volcanicity are associated with weaker parts of the crust. These include;

They are common along the zones of plate tectonic convergence mainly to oceanic and continental plate where the oceanic place subjected into aesthnosphere and get heated producing magma then rises through the line of weakness.

A long the zones of divergence where the crust spread apart giving to a line of weakness through which magma pass.

In regions of faulting like along the great East African rift valley.

In regions where folding as fractured the crustal rocks.

WORLD DISTRIBUTION OF VOLCANOES AND LAVE PLATEAUS

Economic importance of Vulcanicity

Positive importance:

1. Some lava out – Pouring have weathered to give fertile soils. These regions are of important agriculture value. E.g. Deccan plateau in India.

2. Volcanic activity sometimes results in the formation of precious stones and minerals. These occur in some igneous and metamorphic rocks e.g. Diamonds of Kimberley, Copper deposits of U.S.A.

3. Some hot springs are utilized for heating and supplying hot water to building in New Zealand and Iceland.

4. Volcanic eruptions also provide geothermal power, which can be utilized for electric generation. Geothermal power is used in Kenya and Ethiopia

5. Volcanic eruption can attract tourists and lead to the development of tourist industry in the country.

6. The calderas resulting into lakes can be useful for fishing, irrigation.

7. Volcanic activities result into the formation of different volcanic land forms such as Volcanic Mountains, which are attractive to tourists.

Negative significance

1. Volcanism leads to migration of people from areas of volcanic activity.

2. Leads to great loss of life

3. Leads to destruction of property.

4. Volcanic eruption causes environmental degradation

5. Occurrence of earthquakes due to the movement of magma through the lines of weakness (fault lines)

6. Some volcanic features create barriers, making construction of communication lines difficult and expensive e.g. In the Yalta Plateau.

7. The rugged nature of some volcanic landscape discourages economic activities such as agriculture and the establishment of settlement.

DENUDATION AND DEPOSITION

Denudation refers to all processes that involve the breaking, wearing away and lowering of the

surface of the earth. Denudation involves several process such as weathering, Mass wasting, Erosion and Transport of materials.

Deposition:This is the laying down or release of the rock particles on the surface,It can be by: 1.Water producing features like flood plains.Natural Levees , alluvials fans,beaches etc. 2.By ice producing features like out wash plains ,clay plains,moraines ,eskers drumlins and

kames.

By living organisms producing features like coral reefs.

By wind producing feature like loess plains and sand dunes(barchans and seifs)

By evaporation and precipitation producing features like salt deposits.

I. WEATHERING

– Is the physical disintegration and chemical decomposition/decay of rocks in situ / when exposed to weather.

Weathering does not involve transport, in weathering there is no large scale movement

thus weathering doesn’t involve transport.

In situ in the original or appropriate position.

Types of weathering

There are two types of weathering

Mechanical / Physical weathering

Is the breaking down of rocks into small particles / fragments without involving (undergoing) any chemical means / changes

Mechanism (How does it take place)

Temperature change

This is best noticed / occurs mostly in hot deserts / tropical deserts. (Dominant) where there is large diurnal range of temperature during the day, temperature is very high (450c). The rock surfaces are intensively heated which causes rapid expansion which causes cracks on the surface of the rock (Parallel cracks).

During the night, temperature falls rapidly (20C). Range is 430C. Rapid contraction on the rock surface which will increase cracks which are vertical / perpendicular to the surface.

This process takes a long time (100years) and results to the peeling of

rocks on the surface “Onion Peeling”

The process is called EXFOLIATION.

A smooth mould which is called exfoliation dome remains after exfoliation has taken place

Exfoliation particles are called Screes. These are particles which collect on the foot of a hill / rock mass This happens on daily bases.

Why do we have diurnal range of temperature?

Because of absence of cloud cover. The incoming solar radiations reach at maximum and causes high temperature. And there is rapid cooling because the heat is not retained hence it removes.

Frost Action

This is a process which is dominant in temperate regions and in high mountains (mountainous regions)

The process occurs during summer where there melting and during winter there is freezing. It is a process which occurs seasonally.

When water freezes it expands by 9% of its original volume this develops a crack. When the  ice  melts it will fill the crack and when the next winter reaches the water will freeze and will expand the crack. This is continuous action which happens seasonally and eventually will lead to the disintegration of the rock.

Action of living organisms: (biotic / biological).

a) Plants action
– Root Penetration. As the plant grows the roots grow also and penetrate in the surface which causes cracks on the ground.

b. Animal action.

Micro-organism (barrowing animals i.e. roddents,rats):

These animals make some holes on the soil whereby their activities in the soil allow weathering to reach the bedrock. This makes the soil loose hence the rocks break down.

Macro-organism (trampling animals and man i.e. cows, elephants) :

These animals encourage soil erosion also poor agricultural methods used by man and deforestation expose bed rock to weather.

Alternating / alternate wetting and drying: –

This can be dominant in coastal areas. During high tides the rock is exposed to water which causes contraction to the rock and during low tides the rock expands because it is not exposed to water. This happens daily as a result it weakens the rock and hence it breaks (it is exposed to weathering).

Salt Crystallization:

When salt water is in the rock, during dry time the water will evaporate and salt crystals will remain, these crystals are solid they will occupy space

by expanding the rock and when the salt water returns the rock will contract. This continues and will hence develop a crack.

Pressure release or unloading

It always occurs in large scale than other processes discussed it resulted from the unloading rocks during exhumation. As the overlying materials are removed the consolidating pressure are released and the rock tends to rebound. The stresses created open up joints and bedding planes. Rarely the process result to direct disintegration but is seems to be a wide spread means by which rocks are weakened and make more susceptible to other weathering processes.

ii) Chemical weathering

This is a process of decaying or decomposition of the rock when exposed to weather. In such process there is chemical change which weakens the rock, and makes it easily to break down by other forces

/ weathering agents.

Chemical weathering occurs under the following processes:

i. Oxidation

ii. Carbonation

iii. Hydration

iv. Hydrolysis

v. Solution

OXIDATION:

Is the addition of Oxygen to the rock mineral. A process whereby certain mineral compounds takes additional oxygen. In that process it becomes weak and easily broken down. This is common in clay which contains iron compound when iron rusts it is oxidation.

CARBONATION

This process takes place where there is plenty of carbon dioxide and moisture.

Is a chemical process where weak carbonic acid reacts with calcium carbonate to form calcium bi carbonate which is soluble compound which is readily removed in solution by ground water.

Carbon dioxide will dissolve in rain water which will form weak carbonic acid, when reaches on the ground will react with lime stone in the rock to form calcium bicarbonate. The solution will come out of the rock and make the rock weak.

HYDRATION

Some rocks take in additional water molecules which causes stress to the rock / expansion and that expansion causes internal stress and fracture. In this case the rock becomes weak and easily broken down by other processes.

HYDROLYSIS:

This process involves hydrogen (in the water) combining with certain metal ions (in a mineral) that is the water and the mineral react chemically which gives rise to the formation of different chemical compounds.

H₂O reacts with minerals rocks and carbon dioxide to form clay minerals, silica and potassium carbonate which is soluble and leaches out leaving the rock weak.

SOLUTION

Nacl + H₂O = salt solution.

Where rock comes into contact with water and salt it disintegrates.

BIOTIC WEATHERING

Associated by plant roots, where by root tips are secretes acid which react with rocks and they disintegrate

Decaying organs produce organic acids which when come into contact with rocks it disintegrates.

Organic acid of decaying vegetation – weathering of rock

FACTORS WHICH INFLUENCE THE RATE OF WEATHERING

1.THE NATURE OF THE ROCK

– soft or hard

Mineral composition. – This varies from one rock to another and hence affects its resistance some rocks tend to be stable, while others are unstable depending on their mineral composition. For example, rocks like granite with quartz are stable and very resistant to weathering hence weathering process will be slow which rocks which are unstable like basalt which have lower silica undergo weathering very fast. Iron minerals undergo oxidation very fast; rocky salt (sodium chloride) rocks dissolve quickly in water.

Plane of weakness or rock structure

Through joints, weathering takes place very fast, since acids can penetrate easily into the rock and cause the rock to decay during chemical weathering. And frost action tends to be fast in the areas where the rocks have some cracks.

Color

rocks with dark minerals (olivine) heat faster than rocks with light

minerals. Thus, the rate of weathering by temperature change is higher to rocks with dark minerals.

2. CLIMATE

Variation of climate cause differences in the rate and type of weathering. The main climatic controls are of temperature and humidity. However the role of climate in weathering is extremely varied region to regions depending in temperature and rainfall patterns. Hence type of climate determines the rate and type of weathering.

Equatorial regions – These are characterized by high temperature and rainfall throughout the year. Chemical composition of rocks is very active in these latitudes due to high temperature and high rainfalls totals.

Tropical (Savannah) regions – These are characterized by the seasonal variation of rainfall and temperature i.e. there is dry and wet seasons. Due to the presence of both

seasons, both chemical weathering and mechanical weathering takes place. Chemical weathering during wet seasons and mechanical weathering during dry seasons.

Hot Deserts – These are characterized by large diurnal temperature range i.e. day temperatures are extremely high while night temperature fall more rapidly. There is low amount of rainfall and excessive evaporation. Both mechanical and chemical weathering take place mechanical by the process of exfoliation and (frost action) and chemical by salt crystallization due to excessive evaporation.

Mountain regions – These are characterized by high humidity and low temperature. Hence, frost action is active in tropical regions where there is an

existence of mountains with height above 430m like Elgon and Ruwenzori, frost action is also common.

3. RELIEF (Slopes).

At steep slopes the rate of physical weathering will be fast but chemical weathering is retarded because H₂O moves (no penetration of water).

On lowland, physical weathering will be slow because weathering is protected by weathered materials and chemical weathering will be faster because water is there and will influence weathering.

Under relief there is aspect -is the position of a place in relation to sun rays. North facing slopes do not face sunlight hence it is less developed and weathering takes place slowly but in the south facing slope, weathering takes place fast and well developed soil and good vegetation.

In the tropical regions there is no aspects

In mountainous regions frost action takes place actively.

4. ROCK AGE.

Old rocks are more susceptible to weathering as they had enough time been much subjected to different weather forces compared to young rocks. It is thus, the rate of weathering is higher to old rocks compared to young rocks.

5. BIOTIC ACTIVITIES

Biotic activities contribute a lot to weathering in varied ways and include;

Penetration of plant roots causes physical destruction of rocks.

Some plants and animals secrets acid from their bodies leading to decomposition of rocks.

Burrowing of animals also cause mechanical weathering

When the living organisms in the soil respire, give out carbon dioxide gas. The gas dissolves in water to form carbonic acid, which cause decomposition of rocks.

In other way round, thick vegetation cover, such as tropical forests acts as a protection against physical weathering and also helps to slow down the removal of weathered materials.

Human activities, poor methods of agriculture expose the bed rock to weathering.

Study Questions

1. Discuss exhaustively the role of water in the weathering process.

2. Where and for what reasons mechanical weathering is a dominant process.

3. “Mechanical weathering and chemical weathering processes are interdependent and

complementary” Discuss.

Weathering is not influenced by force of gravity but mass movement is influenced by force of gravity.justify

II. MASS WASTING (Mass Movement)

Is the down slope movement of weathered materials under the influence of gravity. In this movement, there is no transporting agent.H₂O is involved as a lubricant and not a transporting agent. Water helps to reduce friction of particles within weathered materials. And also water adds to bulkiness, this will facilitate the process of mass wasting.

Types of mass wasting

Two types according to the speed of movement

i. Slow mass movement

ii. Soil creep

iii. Solifluction

iv. Talus creep

v. Mudflow

vi. Rapid movement

vii. Slump

Rock slide or sometimes both slump and rock slide are called “land slide”.

Rock fall

SOIL CREEP

Is a steady downward movement of soil on all sloping land. Rain water lubricates soil particles and enables them to slide over each other.

Is the slowest and imperceptible movement of weathered material, mainly fine soil down a gentle slope.

Soil creep can be manifested through mounds of soil behind the walls, tilting and cracking of walls, bending of trees, fences and telegraph poles as well as cracking of the road.

In equatorial regions creep is often disguised by dense vegetation cover.

SOLIFLUCTION

Movement of weathered materials under frost areas. It is limited to mountain and cold climate areas where thawing causes a saturated surface layer to creep as a mass over underlying frozen ground. (Saturated soil, gravels and weathered rock).

TALUS CREEP

This is also a very slow movement of angular waste rock of all sizes (talus or scree) down a slope. It is common on the sides of the mountains, hills and scraps. It takes place where free- thaw action is common especially in the highlands and high latitude regions.

Large talus sheets move mass especially in mountains where freeze – thaw is frequent. Talus moving down a valley in a long stream is a rock glacier.

Movement of large volumes of unconsolidated materials which are super-saturated with water, the materials flow as semi-liquid mud (as slurry) with boulders and gravel embedded in mud.

Large volumes of unconsolidated material, super-saturated after heavy rain, become plastic and flow common in acid and semi arid region.

SLUMP.

Massive rocks overlying weak rocks saturated by heavy rain common on over steepened slopes. Large masses of rock and debris.

ROCK SLIDE

Is sliding movement of the slab of rock down the steep slope, no rotation is involved. It can be triggered off by earth quake or human activities like mining or cultivation.

Surface rocks sliding over a slip surface formed by bedding or fault planes dipping sharply down slope.

ROCK FALL

Is a falling movement of individual rock blocks with boulders along a precipitous (steep) slope of a mountain or along road cuttings or cliffs.

Precipitous slopes in mountains where well jointed rocks may be loosened by freeze –thaw.

Rocks accumulate as a talus slope along valley sides.

FACTORS WHICH AFFECT THE NATURE AND SPEED OF MASS WASTING

a). The degree of saturation and nature of weathered material

The more saturated the weathered material is the faster the rate of movement.

Because there is more friction between particles.

Depth of weathered materials, weakly bedded and steep dipping the faster the rate of movement.

b). Gradient.

Steeper the slope, the faster the rate of movement and vice versa.

c). Climate.

Amount of rainfall, nature of rainfall , the annual and day temperature ranges.

Heavy rain or alternative freezing and thawing encourage movement. Heating and cooling.

d). Vegetation cover.

Absence of vegetation cover to hold the materials will increase the speed of mass wasting.

e). Human activities.

Mining, overgrazing and keeping of animals are among the ways in which man has affected the stability of the surface and facilitates the rate of move.

f). Earth movement

Especially earth quake which can disturb the rocks and encourage mass wasting.

Effect of mass wasting

1. Loss of life.

Example, for those who build their settlement down the hills, rock fall many occur for mountain climbers the avalanche may fall.

2. Destruction of property.

Example, those farms which are on the foot of the hill or on a slope may be destructed by mass wasting (soil creep, land slide, rock fall) buildings, roads, railway lines, river all these become blocked by mass wasting and land slide.

3. Attract tourism.

The resulting feature after mass wasting has occurred can arrange the rocks in such a way that is attractive to the human eye. Also human beings like to see the effects of a disaster first hand.

4. Land degradation.

Removal of fertile soil from the land. It leaves scars which is less value than the before land.

5. Formation of fertile soil on the foot of the hill where weathered materials have accumulated.

6. Can dam a river to form temporary lakes. But the weathered materials are loose hence water will remove the weathered materials and the river will continue to flow.

PRECAUTIONS:

1. Afforestation and reforestation on slope lands. This will help to the stability of weathered material, will reduce rate of move.

2. Control human activities. Especially poor methods of agriculture (contour cultivation will stabilize the farm).

3. Avoid establishing settlement in areas which are prone to mass wasting. ü    – Making of terraces across of slopes.

Study questions.

Carefully distinguish mass wasting from weathering.

Mass wasting    weathering

Influenced by gravity

1. Disintegration and decomposition of rock.

Movement of weathered materials

2. Types include physical and chemical

Types include slow mass movement and rapid.

3. Generally restricted to material breakdown in place

Processes range considerably in rate

4. Is a surface phenomenon

EROSION

Is the detachment and removal of weathered materials from the surface of the earth surface by agents of erosion.

OR Is the process of breaking up and wearing away of exposed rocks by moving water,wind and moving ice.

Agent of erosion;-

There are four agents of erosion

Running water

Wind

Glaciers (moving ice)

Waves and tidal currents.

EROSION BY RUNNING WATER

What is running water?

Is any water which falls on the ground and flows down slope under the influence of gravity.

When water in running on the surface performs three functions ,that is Erosion,Transportation and Deposition.

What happens when water fall on the surface of the earth?

Percolation – When H₂0 is absorbed in the ground.

Evaporation-Rain

Surface run off- Is most effective agent of erosion over the earth surface

Surface run off cause’s soil erosion

Types of erosion

Sheet erosion.

Uniformly removal of upper soil without well defined channels.

Removal over a large area of a top layer of soil and other fine materials by a thin sheet of H₂0 flowing over a fairly smooth surface.

Rills erosion

Removal of upper soil from surface with well defined channels called rills. The impact of rills is more effective than sheet erosion.

Gully erosion.

If rills are not checked they will collide and come larger and to form big channels called gullies. Removal of soil by these gullies is what is called gully erosion. Gullies are also grooves or depression of v-shaped.

Splash erosion.

Is the rain drop impact on the surface. Particles are displaced by rain drops (loose dry materials).

Impact (result).

Formation of small channels which will leads to formation of badlands. ( smooth land – bad land which is less useful)

Bad land

Gullies

Rills.

EROSION RIVER, WIND, GLACIER AND WAVES

RIVER

Mass of water flowing in a natural channel over the earth surface from the high land to low land under the influence of gravity.

TYPES OF RIVER

Perennial River:-These are rivers which flow throughout the year .The source of these rivers is the region with a abundant and well distributed rainfall throughout the year. E.g Nile River(Africa),The Congo river(Africa) and the Amazon in South America.

Intermittent Rivers:-These are the rivers which flow only during the wet season in the regions which receive seasonal rainfall.

Ephemeral Rivers:-These are the rivers which appear during the rainy season in the areas which experience very little rainfall especially the desert.They tend to disappear immediately after the rain season has stopped.

River vs stream

River and stream are used interchangeably.(used the same way)

Terminologies associated with rivers.

Rivers head. (River source).

Is a point where the river or stream begins. It makes its first appearance on the surface / it is the highest point on a river system.

Possible river sources

Lakes – R. Nile in Lake Victoria.

Mountains with plenty rainfall e.g. Rockies and Appalachian ( Mississippi river ) R. Ganges, Indus (Himalayas)

Springs.i.e. Thames River in England.

Melting ice i.e. Rhine river in France.

River mouth.

Is a point where the river ends. The lowest point / base level of the river.

Possible river mouth

Oceans – River Rufiji – Indian ocean.

– River Nile – Mediterranean Sea.

Lakes – River Kagera – Lake Victoria

-River Malagarasy – Lake Tanganyika.

Swamps

Others rivers – (Blue Nile meets with White Nile)

Water shed/ catchment area/River basin.

Is a collecting ground of single river system. Where a river collects its water.

Tributary:Is a branch of river pouring its water into a main river.

Distributary: Is a branch of a river which collect its water from the main river.This is more prominent in the lower stage as is associated to delta formation.

Divide:

Is a highland separating two adjacent river systems.

River system:

The main river and its tributaries ( distributes)

River valley:

Lowland between two hills of drainage basin where at the bottom the river flows. (At the lowest point a river flows)

River bed:

Is the actual part of the river which is covered by water (flowing water).

River load:

Is the materials carried by running water.

WORK OF RIVERS

Works of a river includes three processes.

Erosion

Transport

Deposition

RIVER EROSION.

Is the progressive removal of materials from the floor and side of the river / progressive removal of materials from the river bed.

Vertical erosion. – Deepens the river channel.

Section across a river channel.

Lateral erosion – Widens the stream.

Head ward erosion – Takes place on the upper course which lengthens the stream.

The process of river erosion is accomplished through four interaction process.

Hydraulic action

Refers to the force of moving water which is able to remove loose materials such as gravel, sand and silt and which is able to weaken solid rock by surging into cracks in the rock [from the sides and the floor of the river]

Corrosion

Is solvent action of water (solution). Process of removing soluble materials by moving water e.g. Limestone or Calcium carbonate.

Corrasion

Wearing away of the river bed by the load of the river.

Attrition

Impact of the load of the river upon itself, this takes place because the rock fragment which made up the load are in constant collision with each other.

RIVER TRANSPORTATION

Movement of materials from one place to another by the river. Mechanisms:

Suspension.

A lite material whose specific gravity is less than one is carried above the floor as suspended load.

Saltation

Those particles which are large are transported in series of hops (bounces from one point to another, touches the floor at given interval).

Traction.

Transportation of the load by dragging on the floor. Continuously touches the floor.

Solution.

If river passes through soluble rocks, the materials dissolve in water and become soluble and cannot be seen.

– Transportation of the load depends on the energy and power of the river.

Power – ability to do work but power depends on energy to be able to perform a certain work.

Energy of the river

Depends on

i Volume

ii Velocity.

Volume + Velocity = Discharge.

The volume of the river is how large the river is (size)

ii. The velocity – How fast the river flows.

Large volume will have more energy than a slow flowing river also the larger the velocity the greater the energy.

Volume and velocity of a river is what is called river discharge ( is the number of cubic meters per second passing through a particular section river ) (m3/sec)

This discharge is measured by a current meter which is placed in the river which has a dialogue (current meter) which automatically records the energy of the river at any point.

-The velocity of a river varies from one place to another across the channel, Due to ;

The middle part of the river has maximum velocity.(maximum energy ) because the friction is less.

Velocity of the river varies with gradient. A river with steep gradient has high energy compared to a river.

The shape of the channel also has great influence on the energy of the river.

– A shallow and wide channel has less energy because friction is less compared to a wide channel.

Channel B losses more energy through friction than channel A but channel C has the greatest available energy due to the channel.

Due to the large size of the channel.

It is important to note the difference between the river channel and the river valley.

THE HEIGHT OF A RIVER ABOVE THE BASE LEVEL OF THE RIVER.

Base level of the river.

Is the lowest level of a river can erode. When a river ends on the lakes or oceans is the base the river.

-The height of a river above its base level gives it what called potential energy (P.E). (Energy due to position.)

-When water flows, potential energy is converted into kinetic energy which does the work of the river.

A river uses its potential energy to.

To overcome friction in

the river bed.

To erode

To transport the materials /load.

The rate of erosion along the river channel depends on;

Volume of the river.

The larger the volume of the river the higher the rate of erosion.

Velocity.

The higher the velocity the greater the rate of erosion (greater the rate of distraction)

The type of rocks over which a river flows:

A river can flow over soft rocks, erosion will be more and rate of distraction will be high but if flows over hard rocks, erosion will be low.

Type of cutting tools (type of load the river carries).

To do corrosion if it takes large load the rate of erosion will be high compared to a river which carries small load the rate of erosion will be low.

RIVER COMPETENCE AND RIVER CAPACITY
RIVER COMPETENCE

Is the ability of a river to carry large load in term of size individual particles.

At particular places and particular velocity.

A river competence is high where a river is narrow because the energy is higher compared to large slow moving water because energy is slow.

River capacity

Is the ability of a river to carry a large load in terms of the volume.

A large slow moving river has high capacity but low competence and vice versa.

A fast flowing moving river has high competence but low capacity.

The ultimate goals of a river are to being the land above the sea level to its base level. But this cannot be achieved because there is adjustment.

RIVER DEPOSITION.

What is river deposition?

Lay down /dropping of the load transported by a river. Why deposition.

It deposits its load when the energy of the river is insufficient to carry the load further.

When does this occur?

When the volume of the river decreases.

When the does the volume of the river decrease and force deposition?. When it enters arid and semi-arid regions (dry land /hot desert) because evaporation increases and percolation increases (more reduction of water in the channel as it Wets the ground) or when it enters regions of porous rock and limestone regions or in the dry seasons (droughts) because no addition of water from rainfall.

When its velocity decreases (speed).

When does the speed decrease? When the gradient falls velocity decreases and energy decreases

When a river enters a lake or swamps the speed decrease because it meets with another force.

When a river enter ocean/sea. Because it encounters some waves and tidal currents (encounter forces).

The stronger the encounter force.

When the river channel widens. Friction increase where by the energy decrease and leads to deposition.

DEVELOPMENT OF THE RIVER VALLEY

Long profile and cross profile of a river.

Long profile of a river:

Is the whole length of a river from its source to its mouths.

Cross profile of a river:

Is the width across the river from bank to bank.

River erosion leads to development of varies features along the valley as erodes from sources to mouth. These features are studies acquired to stages of the river.

THREE STAGES OF A RIVER

Upper / torrential / youthful stage Middle / mature

Lower / old /plain

LONG PROFILE OF A RIVER FROM ITS SOURCE TO ITS MOUTH

CROSS SECTIONS

CHARACTERISTIC FEATURE OF YOUTHFUL STAGE /UPPER

i. Deep, narrow valley (v-shape) because vertical erosion is dominant. Therefore it deepens the valley.

ii. Valley has step gradient –The speed of the river is very high

iii. Presence of pot-hole

iv. Presence of interlocking spurs

v. Presence of water fall and rapids.

POT –HOLES

–These are circular depression on the river bed.

-H₂0 swirl when it passing on that depression

– Formed where the rock is softer than the surrounding rocks due to uneven river bed. Erosion of fast flowing water swirls in the depression deepening and widening it.

-A. pothole can be much wider and deeper

depression

Form at the base of a water fall and form a plunge pools.

Presence of inter locking spurs.

What are spurs?-is a high land projecting into a lower land. A river at the upper course cannot overcome obstacle it will swirl around the obstacles.

-Spurs alternating on either side of the river interlock/overlap

Waterfalls
-A sharp breaks on the river channel where the water falls from higher level to a lower level.

Causes of water falls

i. Difference in rock hardness

ii. Uplift of land (tectonic forces ) (earth movement)

iii. Glaciated valleys.

iv. At a cliff.

v. River rejuvenation.

vi. Waterfalls formed by difference in rock hardness

vii. Inclination of the hard rock. Rock layer is horizontal

viii. Rock layer dips up stream

Rock layer is vertical. (vertical dyke

Example of water falls

Gersoppa falls    India

Victoria falls    Zambia

Niagara falls    between lake Erie and Ontario

Living stone falls    Zaire river

Rapid

Is a part of stream where there is sudden increase of speed/velocity of water in a stream/river.

Causes of Rapids/when do they occur

When the hard rock dips gently down stream Rapid.

During recession of water fall (Retreats)

Gorges
– An elongated steep sided trough/hollow (deep) always occur where waterfall retreats. (Waterfall migrate up to river)

Canyons – Formed by H₂O recession or uplift of the land (areas of up lifting) e.g. the grand canyon.

CHARACTERISTIC FEATURE OF MIDDLE/MATURE STAGE

Valley has open V – shaped valley ->because lateral erosion is dominant.

The speed of the river has decreased because slope decreased volume/ has increased because more tributaries join it and this in turn means that the river load increases.

River beds are pronounce because of maximum erosion on the concave side and even undercutting of the outside of the curve, the concave banks stand up as river cliff ;because there little erosion or even deposition on the inside of the bend ,the convex bend

slope gentle as clip – off slopes (smoothed ends of spurs ). The river starts to meander and river plains are formed.

Bluffs – As spurs are removed, their remains form a line of bluff on each side of the valley floor.

Deposition start to take place on a fully mature valley

CHARACTERISTIC FEATURE OF OLD/PLAIN STAGE

The gradient is very low and a river develops meander aimlessly along a wide flood plain. Its energy has decreased hence cannot overcome obstacles it then create banks

The main work of the river is deposition and deposition it forms some features on the river bed e.g.Braided stream,Ox-bow lakes,natural leaves ,delta etc.

Braided stream

Due to deposition on the river bed will build some mould and causes the river to split into several channels which rejoin and split again.

Formation of oxbow lakes

Forms when meander is so acute that only a narrow neck of land separate the two ends of the meander.

Neck of the land separate 2 concave banks where erosion is active.

The neck is ultimately out through; this may be accelerated/often during river flooding.

Deposition seals the cute –off which become an ox –bow deposition take place along the two ends of the cut off and eventually seal off to form Ox-bow Lake.

Production of the natural levees:-Formed through successive flooding near the river because as the water flood out of the main channel its speed is immediately checked by friction with the banks and the heavier sediments are drooped first.

-Ridge/embankment on the sides of the river formed caused by river deposition especially after flooding.

-Deferred tributary –Is a tributary which flow parallel to the main river which tries to enter it but the main river is high above the flood plain.

-Deferred junction –Is the point at which the tributary enters the main river.

Example; Ya-zoo streams flows for 200km without managing to join the river Mississippi.

Formation of delta-

What is delta: Is a large, flat low lying plain on the river mouth where deposition takes place.

Deposition continues to takes place on the river mouth which causes the river to divide into various channels called Distributaries

Types of delta

There are many types of delta. But the main types are;

i. Arcuate delta.

ii. Estuarine delta.

iii. Bird foot delta

Arcuate delta

– It is made up of many distributaries.

-The load is composed of coarse and fine materials.

-It is triangular in shape.

Examples; Nile, Ganges, Niger, Indus and Hwan Ho.

Birds foot (digital)Delta

Has few and long distributaries

-Triangular in shape -Fine and very fine sediments.

-This will occur where the river energy is very low.

Examples; Mississippi, Omo River in Ethiopia. And also the wave energy is low:-deposition takes place comfortably.

Estuarine delta

– Has a shape of estuary (sub merged river mouth) deposition takes place on the sub merged part of the river (estuary). It is also triangular shaped.

It has no distributaries.

Examples; Elbe delta (Germany), Vistula delta (Poland).

Formation of floodplains

– Is a broad gently sloping surface of alluvium deposits immediately after the river channel.

Produced by the deposition of alluvial and other materials on the floor of the river valley through which river meanders

Stages in the formation of delta.

The stages in the formation of a delta in an ocean or sea are:-

STAGE 1 :Deposition divides the river mouth into several distributaries. Spits and bars arise and lagoons are formed. Depositions on the banks of the distributaries produce levees which extend into the river or sea.

STAGE 2:
Some lagoons have already begun to fill with sediments which cause further division of distributaries into smaller distributaries. The delta has a more solid appearance though it is still very swampy and is usually well covered with water loving shrubs and threes.

STAGE 3:
Further in filling of lagoons plus the growth of a complete covering of vegetation results in the older parts of the delta coming to stand a above water level and to form dry land.

Conditions necessary for the formation of delta

The river must have a large load and this will happen if there is active erosion in the upper erosion of its valley.

The velocity of the river must be sufficient low to allow deposition

The rate of deposition must be higher than the rate of removal by tidal currents.

There shouldn’t be any obstacles in the upper levels of the long profile.

Why a large river like Congo not have delta?

The river Congo has a large load but a high velocity near its mouth which enables most of its load to be carried far out to sea, there by preventing the formation of delta.

River Niger also has a large load but its velocity near its mouth is low. Much of its load is deposited in its mouth where an extensive delta has formed

Value of Rivers / Economic importance of Rivers

1. Water supply for both domestic use, industrial uses, industrial uses and for irrigation purposes example;

2. Rivers are used for local transport (Navigation) they provide inland ports on their courses E.g. St Louis on River Mississippi in U.S.A.

3. Provide sites for hydro-electric power generation. Harnessing of hydro-electric power is common all over the world. E.g. Mtera dam in Tanzania, Seven forks dams on river Tana in Kenya.

4. Rivers are sources of building materials. Sand for building is scooped from the river beds and valleys like in Machakos in Kenya.

5. Rivers also form sources of various alluvial minerals like gold and diamonds e.g. alluvial diamonds are mineral along the course of R. Orange in S.A and Namibia.

6. River deposit alluvial soils a long their valleys during floods and at their deltas. These alluvial soils are fertile and hence for agriculture e.g. along the Nile valley and its delta in Egypt.

7. Rivers have features, which provide tourist attractions such features are like waterfalls and gorges e.g. Victoria falls.

8. Rivers provide rich fishing grounds e.g. R Nile, R Tanah, River Nguruka.

9. Rivers form natural boundaries between communities, districts, provinces and countries

e.g. Kagera river between Tanzania, Uganda, Rwanda.

DRAINAGE PATTERNS

-Removal of water from the surface

-Drainage pattern is the actual arrangement or layout of its tributaries over the surface.

Factors which influence drainage patterns

Slope –:

This will determine the direction and speed of flow the steeper the flow the higher the speed and vice versa.

The function of structure-

Uniformity whether the rocks have the joints or uniform rock e.g. granite will be different from limestone which has joints.(rock with joints will cause the drainage pattern to follow the lines of weakness but uniformity rocks, the slope is the one which will determine the drainage system.).

Nature of rock-

hard and soft rock .Drainage pattern develop of the soft rock because it is easy for water to penetrate unlike on hard rock, drainage pattern becomes diff to develop Alternating layers, having soft sand hard rock, the drainage pattern will develop on the soft rocks only.

Types of Drainage Patterns

Dendrites-
This pattern has a shape like the trunk and branches of a tree without leaves. The tributaries join one another at a low angle (less than 90) from many directions.

-Develops where there is no structural control because such pattern develops in a uniform

rock, the slope is the only factor which in thence’s the drainage pattern. Example Granite.

2. DENDRITIC PATTERN

2. Trellis –Pattern
develops in a region which is made up of alternate belts of hard and soft rock.

-Shape is rectilinear or almost rectangular in shape

-Tributaries join one another and eventually join the main river at a right angle (900)

-Major control is the rock structure and nature of rock with joints or alternating layers of rocks.

-This drainage pattern gives rise to various types of rivers (stream)

(s) Sub Sequent River
– Is any tributary which joins the consequent stream at a right angle.

(c) Consequent river –
This is the main river which flows down slope.

4. TRELLIS:

(o)

Consequent stream

Any stream which flows in the opposite direction to the consequent stream and join the subsequent stream. Almost right angle.

(MC) Minor Consequent river–

A stream which flows parallel to the consequent stream and joins the subsequent stream.

Radial – Shape is like a spokes of a wheel. (Bicycle wheel) that radiates from the centre which can be a conical hill (volcano) ->Develops on a volcano. The major control is the slope. E.g. Granite, volcanic rocks, basalts.

Centripetal- Streams from various directions converge to the center. Common in inter – mountain basins or basins between highlands .Major control is slope.

Annular – A pattern with streams often joining at sharp angles, but arranged in a series of curves about a dissected dome, basin or crater area. Major control is the nature of the rock.

Accordant and discordant

Accordant –This is a normal drainage system of the river. In this drainage system, the river flows in accordance with the rock structure

and    slope. It follows the line of weakness hence hence revealing the relationship with rock structure and slope. This is described as being accordant.

Discordant – Drainage systems that are opposed to the dominant structure.(rock structure, slope and land forming processes.

Superimposed
– Some rivers have developed a drainage pattern which is in no way related to the structure of the region in which it occurs. The drainage pattern discordant to the structure of the land surface in which it occurs.

-Doesn’t have any relationship with geological structure. It has forced itself to be in a place

STAGES IN THE FORMATION OF A SUPERIMPOSED DRAINAGE PATTERN

Original folded surface.

Region is reduced to a plain due to erosion

Subsidence results in region being buried by new rocks but subsequent uplift sees the formation of a drainage pattern. The main river is draining at right angles to the axis of the original structure.

Tributaries to the main river develop wide valleys in the weaker rocks as the main river erodes vertically it cuts across the ridges of strong rock and form gorges. The stronger rock forms ridges because the weak rocks are worn away and not because the region has been uplifted.

Antecedent drainage – A river pattern disturbed by earth movement (uplift or folding). A river which is capable of maintaining its course after up lift and erosion is called Antecedent. E.g. Ganges River, Snake River and River Colorado.

RIVER CAPTURE (piracy)

It is process where one river diverse the head water of the neighboring river in its own course/valley (upper course)

Condition necessary for river capture to occur

The capturing stream should flow at a lower level than its victim stream (capture stream)

The capturing stream must be stronger and must be flowing at a steeper slope than its victim.

The capturing must be flowing over easily eroded rocks that are weaker rocks.

River rejuvenation.

Processes:

Two stream which are adjacent

There is head ward erosion which makes S extend head ward to C₂

After years of erosion C₂ is diverse to C₁ where all its water enters C₁.

Evidence /feature related to river capture.

Elbow of capture.

Is a point where there is a sharp turn of the river. Is the sharp change in the direction of the river course at the point of capture.

Wind gap (dry valley).

This is a gap between elbow of capture and beheaded stream which is dry. The beheaded stream will not dry because it receives water from other sources.

Misfit stream (beheaded river).

A stream carries less water than the valley depth (less water and becomes too small for its valley). A river which is flowing on a valley which is wider than the size of the river.

Rejuvenation.

Feature of river rejuvenation can be seen in the capturing stream. Examples:

Great berg River capture in S.A, River Volta capture in Ghana, River Niger capture in Nigeria.

RIVER REGIME

Is the seasonal variation of the volume of the water in its channel.

FACTOR INFLUENCING RIVER REGIME.

CLIMATE

Precipitation is responsible for the variation of rainfall, snow melt.

High amount of rainfall and snow melting will increase the volume of the river.

River regime follows the rainfall regime.

During winter, volume decreases and early summer volume increases

High temperature, melting increase and volume increase also during high temperature, evaporation increases and reduces volume.

Low temperature freezing increase and volume decreases, this leads to the fluctuation of water volume.

NATURE OF THE ROCK.

Porous rocks and previous rock allow water percolation; hence much of the water sinks in the ground and reduces volume of water.

Impermeable rock does not allow water to sink hence, increase volume.

SLOPE.

The steeper the slope less the percolation and evaporation, hence volume is maintained. In gentle slope, more loss of water because water stays for a long time hence percolation increases and evaporation increases.

VEGETATION.

Variation matter with the area/surface the rivers flowing, the dry/bare land will have less water during dry season because of the increase in evaporation compared to the river passing throughout the forest.

During rainy season, the bare land will have more volume because there is nothing which will retain the water but the river which passes through the forest, the vegetation retains the water.

NUMBER OF TRIBUTARIES JOINING THE RIVER.

The larger the number of tributaries, the larger the volume and vice versa.

HUMAN ACTIVITIES.

Taking place along the river or the river basin e.g. Irrigation, scheme, during dry seasons tends to reduce the water volume.

Agriculture on the river basin clears the forest whereby they reduces the water volume.(farming activities)

Clearing the land leads to increase in evaporation which reduce water volume.

TYPES OF RIVER REGIME.

There are three types of river regime as follows;

Simple River Regime.

Is a type of River regime where there is seasonal variation of water volume such that there is one high water volume period and one period of low water volume.

These occur where there is one dry season and one wet season most common in the tropical regions. Example, Ruvu, Wami, Ruvuma Rivers.

Double River Regime

(Regime of first degree of complexity).

This is a type where there are two distinct of high water periods which maybe because of snow melt or double rainfall maxima.

This occurs on equatorial regions where they are two peaks of high rainfall e.g. River Congo and River Amazon in S. America.

The volume of the river varies according to those rainfall peaks.

Complex river regime

(Regime of second degree of complexity).

It’s a type of river regime which evidenced the longest river in world with wider

basins and numerous tributaries of different regimes.

They cut across different climates. Example River Mississippi, the river volume isn’t much

affected because it across different climates in different regions.

IMPORTANCE OF STUDYING RIVER REGIME.

All development schemes planned on the river and its valley should have proper knowledge on river regime.

Example, RUBADA – Rufiji Basin Development Project /Authority.

TVA    – Tennessee Valley Authority

Kagera River Development Authority

NAVIGATION

Navigation should be planned and the vehicle also should be planned according to the depth of the water.

During high water level can use a certain vehicle and during low water level certain vehicle can be used (type and size of vehicle)

CONSTRUCTION OF HYDRO-ELECTRIC POWER STATION

Plan for the machines to be placed considering the level of water which keeps on varying. Because during low water level and the machines are placed at a upper position, the water won’t be able to reach and the machines won’t work.

CONSTRUCTION OF BRIDGES

The engineer has to plan before building sometimes water level increase and sometimes decrease. When water level increases, energy increases hence leads to destruction of bridges. To have effective bridges must study river regime so as to make strong bridges which can overcome high energy of the river.

FLOOD CONTROL

Must know the time that flood may occur and the level of water which will increase.

Construction of dams will control floods but also constructing dams should consider the variation in the level of water so as to be able to prevent floods to continue taking place Eg. In U.S.A TVA builder dams to control floods.

AGRICULTURE ACTIVITIES ON THE FLOOD PLAIN.

Example River Nile the consider/depend when the water level is high, irrigation is not important but during dry season, canals are constructed at the level of low water so that irrigation can take place, hence important to know the river variation.

SETTLEMENT.

To establish settlement on the river basin must know the river regime, the settlement must be above the area of floods so that during high water level the settlement should not be flooded. (Areas free from floods)

Concept of graded profile

Consider the river long profile from source to mouth.

Refers to the profile of the river, which has attained a state of dynamic equilibrium, where is there is balance between the rate of erosion and the rate of deposition.

In its simplest interpretation, a graded river has gentle slope and long profile with the gradient decreasing towards its mouth.

It’s concave in shape and smooth due to higher erosion in the middle profile of the river and less erosion at the source (great amount of materials) at the lower course, erosion is less because smaller volume of both of heavy loads and very low speed water and load.

CRITICISMS OF THE CONCEPT OF THE GRADED RIVER PROFILE:

There are several obstacles that normally prevail along the river course, which in term distort the equilibrium that river attempts to attain includes;

-The variation in the nature of the rock on the river bed and banks of the river. Hard and soft rock that offer cliff resistance to erosion.

Climatic variation, for which passes cliff climatic region cannot attain the stage. Variation rainfall and areas.

The presences of water bodies like lakes in the river course. The lakes become the center of deposition of sediments.

River rejuvenation. Either sea level changes, river capture interfere with the attempt to attain equilibrium

Continuous erosion along the river channel can be an obstacle to the attainment of balance.

Vegetation that occupies certain part of a river channel.

RIVER REJUVENATION:

Juvenile – young/youth

Juvenation – process

Repeat /do again

River rejuvenation;

Is the process of renewal of the erosive activity of the river valley after it has reached its old stage.

After reaching its old stage instead of deposition it starts eroding.

Causes of river rejuvenation:

i. Eustatic change (fall in the sea level)

ii. Isostatic change (land uplift and subsidence)

iii. Discharge (increase in the river volume)

EUSTATIC CHANGE

Caused by the fall of the sea level (negative movement of base level) The river profile will have to adjust so as to reach the new sea level.

The sea level has changed from L₁ to L₂

Withdraw of water from the ocean by glacial/during glacial period – fall in sea level.

DIASTROPHIC CHANGE.
(Isostatic).

Fall of the sea level floor relative to the land or rise of the land relative to the sea floor – this will make the river start erosion again from the upstream.

B STATIC REJUVENATION.

Discharge.

Increase in the river discharge by increase in the volume of the river and can be caused by;

Increase in precipitation either melting of ice or rainfall

By river capture, when a weaker river is captured by the strong river the volume of the strong river will increase. This will make the river to start erosion again and will leave some marks /feature in the river valley.

FEATURES/LANDFORMS RESULTING FROM RIVER REJUVENATION

Knick point.

This is a point of a river valley where there is a sharp break of a slope as a old base level joins the new base level after river rejuvenation has occurred.

Note.

If a gradual fall – gentle slope will cause rapid.

Waterfall /rapid.

Where there is a knick point with a sharp break forms a water fall for the river to join the new base level e.g. Along the river Congo there is a knick point at old base level Bathurst fall.

River terraces.(Paired)

Occur on the flooded area. There are the steps or benches on either side of the river valley formed as a result of undercutting of the river due to renewed erosion.

If a river on a flood plain is rejuvenated, the down cutting of the river will produce terraces with equal size.

– If the process of river occurs several times a series of terrace will occur.

-Down cutting is vertical erosion, the volume of the river is the same. This will deepen the river.

-Leaves deposition on the terraces.

-The knick point keeps migrating up stream.

Incised meanders (incise – cut down).

These are the curved bend of the river valley that has been incised into the land’s

surface so that the rivers now wind between steep valley walls.

Two types of meanders

Ingrown meanders – Asymmetrical (the valley is not uniform; one part of the valley is much undercut.)

Occur due to resistant rocks which do not erode fast compared to the other side (concave side) which erosion takes place at a high rate.

Entrenched meander.

Is a steep sided symmetrical meander with side standing vertically and parallel to each other. This is produced by vertical erosion on rocks with almost uniform resistance.

There is fast erosion.

Valley within a valley

It is a deep step sided valley within the former valley of river. When the rejuvenation is fairly rapid to cause large fall of the base level producing steep sided valley.