The Dynamic Earth in Geography Form Five Full Notes PDF
THEORIES
THEORY OF ISOSTASY
Denudation has been going on the continents where tons and tons of materials are removed from mountains and hills and get deposited in ocean; but the hill of mountains are not reduced to the sea level.
WHY THIS IS SO?
The phenomena can be explained by the theory of Isostasy.
Origin of the term is Greek; Made of 2 words meaning ‘Equal standing’ is a state of equilibrium or balance in the earth’s crust with equal mass underline equal surface area. Therefore there is a state of equilibrium.
The theory suggest that the continents and their major features are maintained in a sort of equilibrium or are moving towards that equilibrium.
ISOSTATIC EQUILIBRIUM
Isostatic equilibrium can be disturbed
How? Processes on the surface of the continents.
Denudation
Weathering/mass wasting, transportation, and erosion.e.g removal of material which lower the surface.
Deposition -Building up process (rising of the land)
Accumulation of ice masses and melting of ice masses.
For example
When denudation removes the material from mountains there is pressure released, uplift occurs where the material is removed and there is no Isostatic balance.
If the material is deposited on the sea bed there is compression which result in sinking (vertical movements) these vertical movements causes horizontal movements of simatic material from there is compression has taken place to where there was pressure release
In such process a state of equilibrium is restored.
EFFECT OF DISTURBANCE AT SURFACE AND READJUSTMENT OF ISOSTATIC
EQUILIBRIUM
EFFECTS OF DISTURBANCE OF ISOSTATIC EQUILIBRIUM
1. Earth quakes- Earth movements (gradual)
2. Subsidence +uplift (submerged coast /raised beaches)
3. Faulting -Result to rift valleys or block mountains, lift blocks
4. Fold- Fold Mountains
5. Volcanic eruptions forming different volcanic feature (volcano)
6. Displacement of lithosphere leading to plate tectonic
Evidences of Isostatic movements
1. The depression of the crust in the northern part of America and Europe was due to the weight of ice sheets of vast thickness during the ice age.
2. After the melting these ice sheets, the crust has been rising.
3. Slowly for example, there are numerous former beaches that occur around the coast of Scandinavia. They now lie between 8m-30m above the present day beaches. These old beaches have been raised because of the uplift of the land.
4. The continental shelf around Antarctica is covered with water to a depth of about 750m compared with 180m around other continents.
5. The presence of Rias and Estuaries between the coast lands of Gambia and Sierra Leone.
6. The submergence of forests on the shores of Britain.
IMPORTANCE OF THE THEORY
1. It provides the knowledge on the dynamic state of the earth’s crust that is the earth’s crust is not static but it is always dynamic as it tends to balance itself after some disturbances with the influence of the gravitational force.
2. The analogy that the crust floats on the mantle, just like the iceberg floats on and the ocean or sea water, is so crucial in the understanding of the theories of plate tectonics and continental drift.
3. The theory also helps in deciphering (understanding) how different landforms were formed.
4. It also gives the basic for predicting the future of the crustal state at any particular place on the earth’s surface.
5. It can also help human being in taking some precautions depending on the nature of the phenomena that might have been observed in the course of time, like the occurrence of ice sheets and melting of ice.
THEORY OF CONTINENTAL DRIFT
There are 7 continents Origin of these continents
Profounder
1. Francis Bacon (1620) Expanded earth
2. F .B Taylor
3. Alfred Wegener 1912.
According to his theory ,about 280 million years, the present day continents were united in a single block called Pangaea and surrounded by ocean called Panthalassa. He believed that Pangaea was located near the South pole. Later Pangaea split into two (2)Super-continental i.e Gondwanaland(south Pole) and Laurasia(along the equator in the northern hemisphere).
These two Super-Continents were separated by a narrow water body i.e Tethys sea.He assert that
Laurasia split to form present day N.America, Asia, Europe, and numerous landmasses found in northern Hemisphere-Greenland,Iceland and United Kingdom.
Gondwanaland split to give present day Africa, S.America, Australia and Indian sub- continent, Antarctica and other islands in the southern Hemisphere.
Drift
Since that time the continents have been drifting apart to occupy their present positions. And the drifting is a very slow one about 2cm per year. The drifting is still in progress.
Evidence to support Wegeners theory of Continental Drift
1. Structural evidence ( Jig saw fit)
If the continents were to be brought together it will form one single landmass called Pangaea. Hence proves that all the continents come from one land mass. For example S. America could fit into Africa, N. America into Europe, Antarctica, Australia, India and Malagarasy formed in a single landmass with S. America.
2. Geological evidence
Similar rock types in the coastal margin of the continents for example if you take the rocks of west Africa coastal margin and those of Eastern coast Brazil coastal margin the rocks will be the same (similar ) These rocks where one before the split. (Similar type, age, structure, formation)
3. Biological evidence
The study of earlier life in sedimentary rocks. That reveals life similar fossils of different time where found in different places. Similar animals, plants and e.g. .These fossils are found in all continents hence prove that they all come from one landmass
4. Geomorphologic evidence
Structure of mountains ( fold mountains) e.g. The Alps and Atlas have similar features and where also formed under similar conditions, type of rocks the mountain case, structure, alignment and were formed when Africa moved north wards ending up colliding with the European continent. This gives evidence that the drifting movement took place.
5. Pale-climatic evidence:
The discovery of ancient is in the Congo basin where the climate is warm is used as evidence that the Africa continent drifted from parts which were cold to the current warm parts. For example, Africa has been shifting north wards from the south likewise coal deposit found beneath Antarctic ice caps and Greenland show that they were deposit when the continents had not drifted led to
those places when the climate coast warm. This is because the organisms that led to the formation of those deposits cannot east in areas where there is very low temp.
6. Paleo magnetism (palae-magnetic evidence).
This is the most conclusive proof of the continental drift which was done through pale magnetic dating. When the rocks cooled they were magnetized in the same direction (magnetic North) but pale magnetic dating shows that rocks older than 200,000 years ago from different parts of the earth, have shifted their relative positions magnetic fields show new paths representing relative migration of the earth’s materials
This is evidence that the continents have drifted or have been drifting.
Ocean floor spreading.
Weakness of Wegener / critiques of the theory
1. He did not explain how the movement has occurred / the continental drift processes.
2. He was not a geologist but meteorologist hence he was criticized to have involved in the field where he was probably less informed.
3. Not all continents are able to fit exactly as argued in the jig-saw fit theory, but the theory does not account for this aspect.
4. Other scientists argue that the plant remains might have been spread by aspects like wind, blowing from one continent to another.
Wegner failed to explain the development of glacier in the hot arid Australia.
PLATE TECTONIC THEORY (Unifying theory)
It takes the combination of theory of theory of isostacy, continental drift and ocean floor spreading.
According to this theory, the earth has an outer shell(lithosphere) made up of several rigid piece called tectonic plates.
Geometrical part – The crust is made up of segment called plates, which are of various sizes, Large and small plates. pacific, N. American, Nazca, S. American, Africa, Indian, Antarctica plates
Moments- Movement of the plates. The plates are in motion. Either they are diverging or converging cause of movement – Convectional currents from the interior of the earth’s especially aesthnosphere.
The movements can cause plates to collide or slide past one another. The rate of motion is very slow of the plates relative to one another 1cm to 2cm per year.
TYPES OF PLATE BOUNDARIES:
Divergent boundary
Is a boundary which is created when the plates are moving away from each other. This normally occurs in the ocean, where there are mid-oceanic ridges.
Example
Mid Atlantic ridges
Island Arcs ( volcanoes)
Rift. valley Graben
Convergent boundary
Is boundary where by the plates are moving towards one another
Neutral / trans current boundary-
This occurs when plates are sliding past one another. Normally occur on the Transform faults. (No uplift or submerge of the land (crust)
MECHANISMS OF THE PLATE MOVEMENTS AND THE PLATE BOUNDARIES:
Plates are either continental or oceanic. Oceanic plates are simatic (denser).
Continental Plates are Sialic (light).
CONVERGENT PLATE BOUNDARY
Continental and continental – Both will go uplifted and result to folds and faults
Oceanic and continental -The denser will down lift and lighter will uplift and may result to volcanic eruption and subduction result to trenches for the denser plate.
Oceanic and oceanic – Convergent boundary ( subduction result to trenches both will move down)
Plate Tectonic Theory states that “The lithosphere is made up of rigid segments called the
plates and the plates are in constant state of motion relative to one another”
CAUSES OF MOVEMENTS:
I) Convectional current – During mantle convection some materials rise due to the influence of radioactive heat generation and later moves laterally below the lithosphere. The lateral movements
drag the lithosphere leading to the plate tectonic movements. On cooling the materials sink down to the lower level of the mantle where they melt again due to the constant motion of the plates
II )Upwelling of magma in the lines of weakness for example in the mid-oceanic ridges where by the magma is pushed out of the surface through the weak lines of the crust, in order to form a
new crust. This may result to the cause of movements
Isostatic adjustment – May cause slight movement when trying to create balance.
Cooling and heating of the crustal rocks -Expansion and contraction of rocks. The heat in the interior of the earth (mantle) causes rocks inside to expand and when the heat reduces, the rocks
cool. This process causes the rocks to crack hence leads to the disturbance of the crust and causes movements.
EFFECTS OF PLATE MOVEMENT:
Changes on the plate boundaries which are lines of weakness and on these boundaries, major
Landforms of the earth’s surface are going to be formed.
Diverging plates
Oceanic
Mid oceanic ridges
Oceanic Islands
Rifts e.g. Red sea
Continental
-Volcanic mountain
– Block mountains
-Rift valley
Convergent plate boundary
Collision may lead to subduction and uplift.
Oceanic – oceanic trends (Marianna trenches, Japan trenches )
Oceanic and continental-Volcanic mountains on the coastal boundaries and also result into trenches.
( Continental )- Formation of Fold Mountains. Himalayas ( Indian and Russian plate formed)
Neutral / Trans current boundary – There is neither uplift nor seduction. There is lateral displacement of the plates. N. America, San Francisco – San Andrea’s faults displacement of features of about 1000km.
The plate tectonic areas are areas of instabilities which results to earth quake, volcanoes.
The theory of plate tectonic can help to explain almost all of the landforms on the surface of the earth.
Deep sea Trenches: A sea trench is a long deep valley along an ocean floor.they form along a convergent destructive term of depth.the Mariana in the western Pacific with a depth of more than 36000ft.
Mid Oceanic Ridge: It refer to a giant undersea mountain range made up mostly basalt.It may be more than 80000km long and 1500 to 2500km wide and it may rise to 2.3km above the ocean floor.The feature is associated with a divergent plate boundary.As plate diverge,magma rises repeated and eventually cools to form the mid oceanic ridge.
Example: East Pacific as Nazea and Pacific diverges North Atlantic as North America diverges the Eurasian.
III.Island Arcs:Sometimes basalt eruption along the ridge or near may build up volcanoes that protrude above sea level to become Oceanic Island.They may vary in size.Example:Iceland,Japan,Hawaiian is lands, Mauna Loa,Easter Islands near the East Pacific ridge,west Indies.
IV. Magmatic Arc:It refers to island arcs at sea and belts of igneous activity on the edges of continents such as batholiths in mountain belts. Example:Aleutian Island.cascade volcanoes of the pacific North West,along Andes.
Mountain Belts:At a convergent collision boundary,the sea floor is denser and will be subducted making the ocean thinner and narrower hence collision of the continents.Eventually the oceanic lithosphere breaks off leaving the continental crumple to form mountain ranges.
The thick sequences of sedimentary rocks that had built upon both continental margins are intensively.Example The Himalayas as India collided lided, Alps as African and Europe ,Atlas in Northern Africa.In addition to that at a convergent destructive boundary,young mountain like the Andes form due to the folding of the young sediments.
Rifting and associated features:At a passive divergent plate boundary ,the continental crust is stretched and thinned producing faulty landforms like the great East Africa Rift Valley.The faults
may be path associated volcanic landforms.This may explain the volcanic landforms in the rifted areas of East Africa.
Due to thermal expansion emanating from rising mantle plume,it causes uplift of landscape.
New Oceanic Crust:This is associated with a divergent plate margin where the would be gap is filled with the up welled magma to form a new oceanic crust.
MATERIALS OF THE EARTH’S CRUST
What is an element?
A substance which cannot be split into simple substances by physical or chemical means. Elements are made up of atoms. Atoms are made up of protons which are positive (+ve) charges, electron which have negative (-ve) charge and neutrons which do not have any charge
Elements are about over 100 elements known so far
About 90 elements exist naturally some elements exist naturally but they do not exist themselves they combine to form a compound (some exist independently which others are compound of more than one element.)
Of the 90 element, 8 element are the most a bund and in the crystal rocks. These are:
Element
1 .oxygen
Silicon
Aluminium
Iron
Calcium
Sodium
Potasium
Magnesium
What is a mineral?
-Is composed of atoms arranged in a specific order which is 3 dimensional (crystalline) in structure. OR
-Are naturally occurring inorganic substance made up of elements or compounds which is 3 dimensional (crystalline) in structure.
Properties of Minerals
Definite shape (crystalline)
Is inorganic (naturally occurring substance)
Minerals must be solid
Made up of element or compound
N.B: Only minerals which are inorganic are minerals. Coal is not a mineral because it is not inorganic.
IDENTIFICATION OF MINERALS
In the field:
Its colour-Minerals have different colours
Luster -How a rock reflects the light. (Metallic luster they glitter and non-metallic luster are dull)
Streak -Powder which is obtained by rubbing the rock with a harder substance
For example: Iron will remove a darker streak than the colour of the iron .But if it is not a non- mineral, the streak will be lighter than the substance.
Cleavage -If break the rock it will split into definite shape (definite pattern) e.g. mica break into sheet pattern.
Crystalline – In 3 dimensional
Specific gravity- All mineral have higher specific gravity than water. H2O is 1g/cm3
Hardness -Minerals differ in hardness obtained through scratch test; there is a soft test &
hardest test (Moh’s scale hardness; 10 minerals starting from softest of hardest.)
WHAT IS A ROCK?
Is a more or less uniform mass made up of grains of one or more mineral which is found naturally on the earth crust.
– Are aggregates of minerals.
ROCK CLASSIFICATION
They can be classified according to :-
a) Mode of formation
b) Geological Age
c) Structure
ROCK CLASSIFICATION ACCORDING TO MODE OF FORMATION
According to mode of formation/origin , rock can be classified as Igneous, Sedimentary and Metamorphic.
1. IGNEOUS ROCKS
These are crustal rocks formed by cooling either within or outside of the earth’s crust. (Formed by cooling and solidification of molten materials from the interior of the earth)molten materials can solidify intrusively or extrusive (endogenically or exogenically)when molten material are still within the earth crust they are referred as magma, and when reach the surface they are called lava.
Examples; basalt granite, Quartzite, Gabbro cools and solidifies to form volcanic rock
Igneous rock
Is referred to as mother rock, due to the following reasons.
It is the rock from which other rock owes their origin. This means that other rocks are formed after some forces have operated on the igneous rock. Such forces are like weathering process which led to the formation of sedimentary rocks and metamorphic.
It forms the base for soil formation (pedogenesis) whose minerals composition, structure, texture and depth depend on the nature of the igneous rocks. E.g. soft igneous rocks, soil becomes deep and if a rock is hard the soil shallow.
The igneous rocks constitute the large proportion of the earth crust i.e.: 99%
CLASSIFICATION OF IGNEOUS ROCKS
1) Extrusive rocks (volcanic) :
These are formed when the molten materials (lava) solidifies on the surface.
These rocks have small crystals because they cool fast due to exposure. Examples include Basalt, Andesite, rhyolite, obsidian and etc.
2) Intrusive rocks-
These are formed when the molten magma solidifies within the earth crust. They can be classified as hypabyssal igneous rocks, when they are formed near the earth’s surface and plutonic igneous rocks when they are formed deep inside the crust.
Categories of intrusive igneous rocks
2(i) Hypabyssal igneous rocks-:
These are the rocks which are formed when magma cools and Solidifies inside but near the surface of the earth. They have medium size and examples are like granophyres, Porphyries, and
dolerite. These can be exposed after erosion has taken place to form some rock masses like lopoliths and laccoliths which are usually hypabyssal. Basalt also quartz.
2(ii) Plutonic igneous rocks:
These have solidified deep in the crust and they are seen on the surface only after being exposed by prolonged erosion. Example granite, gabbro, pumice and peridotite.
CLASSIFICATION OF IGNEOUS ROCKS BY THEIR CHEMICAL COMPOSITION
Felsic (acidic)igneous rocks:
Consist great amount of silica and feldspar with very little or no iron or any other metallic minerals examples are granite, granophyres, rhyolite, and obsidian. They are acidic in nature.
Mafic (basic) igneous rocks:
Consist of large amount of magnesium iron and other mineral like aluminium. They are basic in nature because of presence of metallic minerals e.g. gabbro, basalt
Ultra-mafic(ultra basic):
Consist of very large amount of metallic minerals like iron, magnesium and a little amount of silica less than 45% e.g. peridotite.
Intermediate Igneous rocks
With silica content between basic and acidic degree. That is, both acidic and basic oxides are in equal proportions. E.g. Diorite, Andesite.
CHARACTERISTICS OF IGNEOUS ROCKS
They are hard, they are semi precious.
They are formed by cooling and solidification of molten materials i.e. Magma or lava.
They differ in chemical composition depending on the amount of silica contained in them.
They are crystalline in nature (made of crystal)
They may undergo metamorphism to form metamorphic rocks.
They may undergo weathering process and sedimentation to form sedimentary rocks.
They contain minerals like iron, magnesium etc.
They don’t have fossils; therefore they do not contain the remains of skeletons’ of animals.
Because they are made from the interior of the earth.
2. SEDIMENTARY ROCK
Are rocks formed from sediments deposited either by water or by wind or by ice. These rocks are formed by the process of the sedimentation. (Deposition of accumulation and lithification of some weathered particles and other materials). The sediment were laid down in layers or strata, one on top of the other and in time these layers turned into rocks as they became hardened by compression. These are called stratified rock.
-The plane between two layers is called the bedding plane.
-The angle of the titled strata to the horizontals called the dip
All sedimentary rocks are non-crystalline and many contain fossils. Some sedimentary rocks are formed in water .e.g. Inorganic-Sandstone and mud stone; Organic-Chalk, limestone and coral, and peat and coal (formed in swamps). Some are formed on land e.g. boulder cay, moraines and loess (all inorganic).
Those formed in water developed from inorganic sediments some sedimentary rocks are formed chemically and not from sediments.
There are three (3) types of sedimentary rocks;
Mechanically formed;
These are the rocks which have been formed by compaction and these are also referred as classic rocks because they consist of fragments of rocks and rocks materials. Examples; clay, gravels and alluviums (all deposited by water), moraines, boulder clay and gravels (deposited by ice), and loess (deposited by wind).
Organically formed;
These rocks have been formed by the accumulation, consolidation and cementation of the remains of died organisms. They include calcareous rocks like limestone and chalks formed from the shells and skeletons. Coral reefs are so common along the East African coast. These are also carbonaceous rocks formed from plant and remains buried a thousand of years ago under heat and the overlying pressure, the plant remains turned into rocks. Example Coal.
Also there are siliceous rocks formed as the result of the remains of organisms like Diatoms and radiolarians, whose skeletons are rich in silica, Example diatomite rocks.
Example; Chalk and Coral (formed from animals), and peat, coal and lignite (formed from Plants). Rocks formed from organic sediments which are plants and animals remains which accumulate, compact and cement.
Chemically formed
These are the rocks which formed by chemical process. They include the following:-
Carbonates.
Like travertine found in the form of stalagmites and stalactites due to the precipitation of calcium bicarbonate, trona due to the hydration of sodium carbonate solution after the evaporation of water.
Sulphate.
As the result of desiccation and evaporation. Rocks like gypsum, which are hydrated calcium sulphate, may be formed as result of rapid evaporation.
Chlorides.
Which include rocks salt is formed due to evaporation.
Silicates.
Which include flint, sinter and cherty are formed due to the accumulation of silica followed by its compaction.
Iron stones.
Are formed when iron oxide is deposited under a water body and compressed. Examples of such rocks include limonite and haematite (red ferric oxide).
| MECHANICALLY
FORMED |
ORGANICALLY
FORMED |
CHEMICALLY
FORMED |
| Shale | Lignite coal | Gypsum |
| Mudstone | Bituminous coal | Rock salt |
| Siltstone | Anthracite coal | Potash |
| Grit | Coral reef | Flint |
| Limestone | Trona | |
| Chalk | Ironstone |
CHARACTERISTICS OF SEDIMENTARY ROCKS
1. They are stratified and young rock layers overlying the old rock layers.
2. They are non- crystalline.
3. They contain fossils as the result of the accumulation of skeletons and shells of once living organisms.
4. They may undergo changes to form metamorphic rocks, when they are influenced by pressure and or temperature.
5. They consist of some fragments, which were deposited and then cemented to form the rocks.
6. They are soft (not hard).
3. METAMORPHIC ROCKS
These are rocks which are formed when one type of rock changes form after having been subjected to either intense heat, pressure or both. Any rock may undergo changes to form metamorphic rocks e.g.
Sedimentary rocks to metamorphic rocks are:-
Sandstone to Quartzite
Limestone to Marble
Coal to Graphite
Shale or Clay to Slate.
Mudstone to Slate.
Metamorphic to Metamorphic rocks
Slate to Schist
Igneous rock to metamorphic rock
Augite to hornblende
Granite to gneiss.
Causes of Metamorphism
Great heat -High temp. Acting on the existing rock. E.g. Bricks there from mud, also the intrusive igneous rocks can change to metamorphism.
Pressure- Rock can be compressed to form other rock resulting from earth movements.
Chemical reaction.
Pressure + Temperature can form sedimentary rocks to change to metamorphic.
Metamorphism
The process of changing the rock from either Igneous, Sedimentary or Metamorphic rock to metamorphic rock.
Types of Metamorphism
Contact metamorphism
-Rock change by contact, e.g. Intrusive magma will affect other rock and form metamorphic rocks Localized because it is not extensive it only affects the rocks which surround it.
Regional/ Dynamic Metamorphism
– Result from pressure of internal movement which will compress the rocks to change their form. They cover a large area.
Thermal/dynamic Metamorphism
– Combination of heat and pressure which can combine and change the form of the rock.
TYPES OF IGNEOUS ROCKS
| TYPE | FORMED AT | RATE OF COOLING | CRYSTALLINE NATURE | EXAMPLES |
| VOLCANIC | The surface | Fast | Small Crystals | Basalt |
| Rhyolite | ||||
| Trachyte | ||||
| Andesite |
ShallowMediumMediumQuartzHYPABYSSALDepthsize CrystalsPorphyryDoleriteGreatSlowLargeGranitePLUTONICdepthCrystalsSyeniteGabbro, dioriteDiorite
TYPES OF METAMORPHIC ROCK
Original rock Metamorphic rock Granite becomes Gneiss Sandstone Quartzite Clay Slate Shale Schist Limestone Marble
ROCK FORMING MINERALS
These are common minerals which make up large percentage of the rock of the earth’s crust.
These rocks are silicates.
Feldspar – Most abundant of all minerals in rocks. There are 2 varieties
Orthoclase feldspar of complex chemical formula KALSi3O8 a compound of Potassium, Aluminum, and Silicate.
Plagioclause feldspar which contains sodium or calcium instead of potassium as in orthoclase.you
have NaALSi3O8 or CaAL2Si2O8 (plagioclase feldspar) e.g. Basic rock, basalt, gabbro Feldspar have S.G (specific gravity) of 2.5g/cm3
Quartz
Second most abundant
Chemical formulate (SiO2) Silicon dioxide
Hardest common mineral
– S.G 2.7
Has no cleavage
Used for making concrete glass and as a semi precious stone.
Mica. Can be composed of many elements .e.g. aluminum, silicon, oxygen, iron, magnesium, hydrogen, or potassium.
It is flat shiny rock most found in rocks like granite, gneiss or schist.
Carbonates: e.g. CaCo3 found in limestone and marble (Dolomite) Camg (co3)2
Horn blend: Common rock forming mineral dark crystalline mass associated with igneous + metamorphic rocks.
composed on calcium, iron and magnesium silicate.
Magnetite: (magnetic iron oxide) Fe3O4
ROCK CYCLE
Is the relationship in which rocks tend to change from one type of rock. For example, a rock can change from igneous rock to sedimentary or to metamorphic and then go back to igneous rock again.
Processes in the rock cycle
1. At first, the igneous rocks may be formed due to cooling and solidification of magma or lava.
2. Then igneous rock can be attacked by the weathering agents to form sediments which on being deposited and compacted may form sedimentary rocks.
3. Either igneous rocks or sedimentary rocks may undergo metamorphism due to the influence of either pressure or temperature or both to form metamorphic rocks.
4. Metamorphic rocks may undergo weathering and sedimentation to form sedimentary rocks.
5. Likewise, metamorphic rocks may undergo further metamorphism to form other more consolidated metamorphic rocks, like the change from slate to schist.
6. Lastly, rocks that are either sedimentary or metamorphic when subjected to very high temperature, they melt and on cooling form igneous rocks.
This process goes on repeatedly and is an endless process. No types of rock remain unchanged for a very long time.
IMPORTANCE OF ROCK
1. Rocks are important in the formation of soil which is essential for agriculture and plants growth.
2. Storing underground water. Water is stored in the water the water holding stratum of impermeable rocks and can come out as spring.
3. Some rocks are used as fuel like coal and mineral oil.
4. Rocks are also used for building and construction. Rocks like limestone, sandstone e.t.c are used for building houses and roads construction. Limestone is used for manufacturing of cement.
5. Salt extraction. Various Salts are obtained from rocks occurring in some places. E.g. in Tunisia, Morocco there is large deposited.
6. Manufacturing of chemicals, some rocks have salts such as nitrates or phosphates while others have potash. These Salts are used for making dyes fertilizers and medicines. Gypsum is used for making the plaster of Paris and Sand is used for making glass.
7. Mineral deposits. Mineral ores occur in veins of some rocks such as rocks. These ores were formed when magma cooled, valuable mineral extracted from rocks include gold, lead, copper, tin silver, zinc, aluminium calcium and manganese.
8. Some rocks are so impressive such that they attract some tourists to come and view them. In doing so the country gets foreign currency. E.g. Coral reefs.
9. Some rocks such as marble are used in decorating floors of some important buildings such as banks e.t.c.
How does metamorphism manifest (Shows) itself in rocks
By foliation – where by the rock has a distinct grain shown by the alignment of mineral particles, usually resembling stratifications but often in wavy lines.
By cleavage – Which resembles foliation although the direction of cleavage may be quit independent of stratification
By the development of new materials which were not present in the unaltered rock; precious stones and valuable ores may be produced by metamorphism.
By the development of a crystalline structure- in rocks which were originally amorphous rocks.
By the change of rocks which had originally a crystalline structure in to amorphous rock; e.g. marble (metamorphosed limestone and chalk). Slate metamorphosed shales.
CLASSIFICATION OF ROCKS BY GEOLOGICAL AGE
Rocks can also be classified according to age
1. Relative age.
2. Absolute age
1. RELATIVE AGE
Sedimentary rocks only where by the age of rock is done through the deposition.
Stratigraphy– stratigraphical sequences
Arrangement of rock layers (Law of superposition). The rocks which are below are the oldest and the above are the youngest (the new ones)
DIAGRAM Assume that the entire layer has deposit at the same time.
This is only true where earth movement have not distorted the rock layers
Palaeontology
-The study of earlier life as evident in sedimentary rocks. (Fossils)
By studying with the earlier life brought about a
GEOLOGICAL TIME SCALE
What is a geological time scale?
Is a table dating in a chronological order the past events of the earth’s history?
Note: m y = million years
There a four ERA, Cainozoic, Mesozoic, Palaeozoic and Pre –Cambrian
Each era ends with a geological evolution which is seen in rocks and conformists recognized through different rock formation and change in type of life as evidence in fossils.
The eras are divided in periods and periods are subdivided into epoch and this is divided into series and formation.
In ERA,PERIOD and EPOCH process occur at some time and way across the world
Processes occurred before splitting of the continents started from series.
Each ERA varies from another there is variation in time where by pre –Cambrian takes 70% of the GTS.
Major geological event are affecting Africa continent mountains, building ,volcanism , glaciations and e.t.c
GTS gives relative age of rock but do not give the exact years of the rock.
2. ABSOLUTE AGE OF ROCKS.
Modern method of determining age of rocks radio metric dating
This method is based on radioactive element which when they produce heat and another new substance which we call daughter element.
When the daughter element is produced the reaction of decaying stops.
The rate of decomposition disintegration from parent element two daughter element is constant
The new substance produced is used to calculate the age of the rock.
The time taken for parent element to disintegrate to form daughter element is called half life
142 disintegration
-10 protons 82 protons
-22 neutrons 124 neutrons (Half life)
– How is it used to find the age of rock.
It has been taken that 1gm of uranium yields 1 ∕ 760,000,000 of lead a
year.
. : A rock containing burn in it e.g. igneous rock and the weight of lead derived from it is found then age rock = (weight of lead ∕ weight of uranium) x 7,600,000,000.
Example: lead – Uranium ratio in urinite crystal form pegmatite rock is 0.10 The age of that rock will be
0.10 x 7,600,000,000 = 760,000,000
Other elements used to determine the age of rocks.
| Isotope | Half life | Daughter element |
| 1. K – 40 | 1.3 billion years | Ar – 40 |
| 2. U 238 | 4.5 billion years | Pb – 206 |
| 3. Rb 87 | 49 billion of years | Sr – 87 |
| 4. C14 | 5730 billions of years | N – 14 |
– This method provide the absolute age of the rock.
Give a critique on the geological time scale.
Importance of the Geological Time Scale
1. It depits the age of the rocks by showing the time when certain types of the rocks were formed and how were formed e.g. some were formed by glacial deposition while others were formed by volcanic eruption.
2. It also helps in understanding when and how different land forms were formed e.g. the mountains of different types like volcanic and Fold Mountains have been accounted for.
3. By studying the geological Time scale one is able to predict the occurrence of crystals deformation that are likely to take place e.g. by knowing that certain areas have old rocks one may conclude that faulting is likely to occurs in case any disturbance or stress.
4. Geological Time Scale also revel the life record for the plant and animals. This records help in understanding the relationship that exists between living things and the geological time scale process. Plants emerged when the soil had developed and animals came into existence when plants had already existed to provide food take on man emerged.
Weaknesses
The methods that were used in determining the age of the rocks were largely based on estimate due to the limited power of the instruments which were used
Another problem pertaining to age determination has been caused by crustal deformation like over folding, gaps caused by denudation (unconformities) and the intrusions of magma.
There are some modifications made locally in the geological time chart. For example unlike the former geological time chart the current shows that Cainozoic era include the quaternary period. Also some other authorities do not indicate the Paleocene period in their geological time chart.
ROCK CLASSIFICATION ACCORDING TO STRUCTURE
It is the 3rd approach of rock classification.This involve the description of the rock.It may involve colour,size,hardness etc.However in order to classify rocks under this category,we use the term Permeability.
Permeability refers to the rate at which rocks can store water or the ability for water to pass through.Permeability can be divided into;
Primary Permeability or Porosity:
This involves rocks which have pore spaces.The size,alignment determine how much water can be absorbed.Porosity is greatest in Coarse-grained such as gravels,sands,sandstone and lowest in fine grained such as clays,granite.
When all pores are filled with water,the rock is saturated.Permeable rocks which store
water are called Aquifers.
Secondary Permeability or Pervious:
These are rocks which have joints and fis-sures along which water can flow.The most pervious rocks are those whose joints have been widened.E.g
Carboniferous limestone o by cooling E.g Basalt.
Where rocks are porous or pervious,water,leaving the surface dry and without evident drainage e.g Chalk and Limestone regions.Impermeable rocks .E.g Granite,neither absorb nor allow it to pass through them.
GEOMORPHOLOGY
Is the science which deals with development of land forms, (relief features).
MAJOR PROCESS WHICH SCULPTURE THE EARTHS CRUST
There are two major forces;
1. Endogenetic /internal processes
2. Exogenetic /external processes
1. ENDOGENETIC PROCESS.
These are force which takes place beneath under the surface of the earth, and they are categorized as;
Earth movement:
vulcanism
2. EXOGENETIC PROCESS
These are external force taking place on the earth surface.
These are force of gradation;
Destructive process(denudation) (Degradation)
Aggradations (constructive process. (Deposition)
INTERNAL FORCE.
Earth movements;
Lateral and Vertical movements
Diastrophism
Is the movement of the solid crust (lithosphere which is made up of upper mantle and crust).The movement can be gradual or rapid. Gradual is the slow movements like what happens in the isocracy.
Can be rapid or sudden as it occurs during earthquakes.
Effects of diastrophism
i. Tension
ii. Compression
iii. Shear
i) Tension
When two forces move /act away from each other, the result strain is called tension which involves the extension of the surface of the crust to produce joints and normal fault
ii) Compression
When two force moves toward one another, it result into compression which involve contraction of the crustal rocks to produce fold and thrust fault.
iii) Shear
When two forces acting parallel to each other through in opposite direction the result is called shear.
Causes of diastrophism
i. Conventional current- in the aesthnosphere
ii. Isostasy -maintenance of equilibrium
iii. Expansion and contraction of rocks due to heating (intrusion of magma between crustal rocks )
FAULTING
What is a fault?
Is a fracture or a crack on the crustal rocks caused by tensional or compression forces.
Compressional will lead to bending and breaking of the rocks
Faulting is the process whereby will result into vertical or horizontal displacement of the crustal rock. Either shear, normal fault.
Types of faults
Normal fault
Is caused by tensional forces in such a case; Foot-wall – Is the upper rock face on the lower side on the fault, it is marked by a low angle (less than 900).
Caused by tensional forces.
There is an up throw and down thrown which bring the displacement of the hanging wall relative to the foot wall, hanging wall is brought down while foot wall is brought up.
Hanging wall
Is the upper rock face on the upper side on the fault wall. It comes out with a very high angle. Any angle more than 900.
Foot wall hanging wall
Foot wall-Is the upper rock face of the lower side the upper rock. Marked by low angle.
NORMAL FAULT
Thrust/Reversed fault
Is the reverse of the normal fault. /is the opposite of normal fault.
This is caused by compression forces.
Hanging wall is displaced upward relative to the foot wall. (Low angle of dip)
Tear / strike / Trans current faults.
This is a vertical structure. The fault plain is vertical or almost vertical. It is caused by shear forces. There is lateral displacement of the crustal rocks. (Parallel but opposite directions).
– Caused by shear forces
Terminologies which are associated with faulting
Shift – Is the total movement of the rock along the fault line.
It involves both slip (the movement along the fault) and throws (the vertical change on the level of the strata).
Heave is the lateral rock block displacement.
Hade is the angle of inclination of the fault plane from the vertical.
Hanging wall is the rock face on the upper side of the fault.
Foot wall is rock face on the lower side of the fault.
Up throw is the mass of rock which has moved upward along the fault.
Down throw is the mass of rock which has moved downward along the fault.
i. Landforms resulting from faulting
ii. Rift Valley.
iii. Block mountains
iv. Plateau and basins
v. Fault scarps
vi. Tilt blocks
vii. Depressions
RIFT VALLEY
An elongated trough bounded by in facing fault scarps along more or less parallel faults
Formation of a rift valley
Theories on formation of the rift valley; There are Many theories but popular ones are 3;
Rift valley by tension
Rift valley by compression
Place tectonics
Rift valley by tension
-Rock layers are subjected by tension
-Faults develop / development of faults
Rift valley by compression
Rock layer are subjected by compression
The side blocks are unstable whereby there is upthrust over the middle block / masses on either side the faults were thrust up higher than the central block (side blocks slide upwards and leave behind the central block)
A rift valley is formed where by the sharp edges are attacked by erosion.
Rift valley by plate tectonic
Rift valley from a single fault. This is from 2 blocks which have a gap in between where by the plates are diverging and magma will well up and attach itself with the diverging plates and the gap the remains will form a rift valley.
Examples of Rift valley
The great African Rift valley
Rhine rift valley (it is between block mountains, Vosges and black forest block mountains)
Mid-Atlantic rift valley
Red sea rift valley
Jordan rift valley
Great African rift valley
One of the most outstanding physical graphic features on the continent.
Extension: starts from the middle east (Jordan – river Jordan)
It extends south wards to River Zambezi (Mozambique). (Beira) its length is 7200km of which 5000km are in Africa.
In East Africa the Rift Valley breaks / splits into 2 branches; Eastern branch it is marked by some lakes; lake Turkana, Lake Magadi, Lake Victoria, Lake Natron, Lake Manyara, Lake Nyasa.
The Western branch is marked by lakes; Lake Tanganyika, Lake Albert, Lake Edward.
The Western branch disappears in Uganda and not noticed in Sudan.
Characteristics of Great Africa Rift Valley
It is bounded by series of fault scarps which are evident in parts of Kenya and N. Tanzania (Manyara)
The floor is almost flat but there are some features which are higher above the sea level like Ruwenzori Mountain which are about 500m above the sea level. And also deep depression likes Lake Tanganyika which is 650m below sea level and the second deepest lake in the world.
The lakes in the rift valley are narrow and deep because they follow the shape of the fault.
The width of the floor of the rift valley varies from place to place from 50 km to 100 km. .
The sides the great R.V have the highlands like mountain adjusted on the sides volcanic mountains.
A MAP OF EAST AFRICA SHOWING THE GREAT AFRICAN VALLEY
BLOCK MOUNTAIN (HORSTS).
These are local / isolated landforms which have been elevated above / raised above the general level of the land. They stand high above the ground like blocks which are flat topped with steep sides. These landforms are common in areas of faults.
Formation
There are two theories;
By tension
By Compression
i. By Tension
Rock layers are subjected to tension
Development of parallel faults
The side blocks will subside and leaving the middle block higher than the others by compression.
Rock layers are subjected to compression
Development of parallel fault
The middle block is unstable and is squeezed up.
Example of Block Mountains
Uluguru mountain
Usambara mountain
Rwenzori mountain
Black forest and Vosges mountain
Sinai mountain
FAULT SCARPS (Escarpment)
Are steep slopes where the land falls abruptly from higher levels to lower levels caused by vertical movements of the crust along the fault line. Can be caused by tension or compression but can be modified by denudation.
Example: Chunya – Tanzania
A fault scarp which occurs across a river result into waterfalls.
TILT BLOCKS
The landscape of angular ridges and depressions formed by series of tilt fault blocks.
Example.
U.S.A Rocky mountain
Somali
Dominated by faults raised
PLATEAU
extensive raised land with sleep sides (table land) e.g. East Africa generally is a plateau / Africa is a plateau in general
BASINS
Are the down warping (sagging). Intermountain basins.
A basin examples: L. VICTORIA, L. KYOGA, GREAT BASIN IN NEVADA, ZAIRE BASIN.
Study Question.
With examples discuss the effects of faulting in East Africa.
Fault is a fracture or a crack on the crustal rock caused by tensional or compression forces. Faulting is the process whereby will result into vertical.
Positive effects
i. Formation of rift valleys e.g. East Africa rift valley
ii. Formation of block mountains i.e. Uluguru
iii. Formation block of plateau and basins. Lake Victoria
iv. Formation of escarpments. Chunya/ kalambo fall in Zambia
v. Formation of the H20 falls where fault scraps occur across the river course lakes from basins of lakes rift valley lakes / river Kagera has change.
vi. River reverse direct due to faulting / the direct due to basins which were formerly flowing west ward and forced flow east ward.
vii. Faulting caused the development of rectangular patterns as tributaries forces to flow through the broken rocks and gets converge to the main river.
viii. Occurrence of hot springs. Spring is the natural outflow of water from the ground in an areas there is weakness i.e. in mbeya Tanzania
ix. Displacement of features e.g. San Andreas fault
x. Leads to earthquake
FOLDING
Compression forces and folding
compression forces can cause folds of the rock layers (strata)
The degree of folding will depend on the intensity of operating forces and the nature of rock.
There are several degrees of fold / types of folds
Simple fold – is a symmetrical fold resulting into upthrow called anticline and a down throw called syncline.
This type of fold has more or less equal limbs, where we have the axis which divided the fold into more or less equal limbs. (Limbs are the sides of a fold) (Symmetrical fold).
Compression force
Asymmetrical fold – Is a greater degree. One limb of the fold is longer than the other. (And gentler) unequal limb. The other is shorter and steeper.
Over fold – One limb / asymmetrical limb is pushed over the other limb.
Recumbent fold – This is a complex fold where one limb on the fold is almost inverted over the other limb, to greater degree. Almost horizontal to the surface.
Over thrust (napped) fold – When the pressure is very great a fracture can occur in the fold (along the crust plain) and one limb is pushed forward over the other limbs. NW highlands of Scotland.
Effect of folding on the earth’s crust
The major effects is the formation of Fold Mountains where three are anticlines and depressions (geosynclines) where there is down fold (syncline).
Fold Mountains
Are categories into old fold mountains and young fold mountains.
Formed during per-Cambrian era e.g. Appalachian, cape ranges, Europe Mountains Ural.
Young Fold Mountains
Recently formed, examples the Rocky, Andes, Atlas, Alps, Himalayas and etc. They form highest peaks over the earth surface e.g. Mount Everest highest peak point, on the Himalayas (over 8000mts).
Global distribution of Fold Mountains
AFRICA:
Atlas – N.W Africa
Cape ranges – S.A
N. AMERICA:
Rocky Mountain – western part
Appalachian – Eastern Part of USA
S. AMERICA:
Andes Mountain – Western side
EUROPE:
Alps Mountain – Central Europe
Ural Mountain – Separates Asia and Europe
ASIA:
Himalayas – Central Asia
AUSTRALIA:
Great Dividing Ranges
Characteristics of Fold Mountains
They are very extensive – covering thousands of kilometers over continents, they are not isolative.
They are high (height) especially young fold mountains make the highest peak e.g. Mount Everest.
Age some are young (narrow and long) and some are old fold mountain.
Some have undergone complex processes that is or genesis like volcanism, denudation (effects of geomorphic processes)
Economic importance of fold mountain positive and negative aspects
1. They are climatic modifiers in terms of temperature and rainfall. By forming high peaks where by the peaks have snow although they lie on tropics.
2. Have dense forests of the world like Asia, North America. They produce hard and soft woods which are used for various uses. (timber-lumbering)
3. Tourism – tourist attraction
4. Source of the major rivers of the world. Rockies and Appalachian (Mississippi river) River Ganges, Indus, Irrawaddy in the Himalayas’, Australia River, China – {R.Sikiang, river Hwang Ito, Yangtze Kiang.}
5. They are source of minerals especially in the Rockies like copper, gold etc. South America also
6. Barrier to communication
7. Topography of some mountains discourages settlement.
DISTRIBUTION OF FOLD MOUNTAINS AND MOUNTAIN ROOTS
Fold Mountains are not uniformly distributed in the continents. They are distributed along the margins of the continents where plates collided. The young fold mountains form their own belts and the old fold mountains also form their own belts as well.
Distribution of Young Fold Mountains
Young fold mountains from the alpine chains. The Alpine chain are the active mountain making belts and they constitute the narrow zones most of which lie along the continental margins. The mountains in these belts were formed during the Cainozoic era. They are curved and each curve is called an alpine arc. These arcs are linked in sequence to form two principal mountain belts as follows:
Circum – Pacific Belt: This rings the Pacific Ocean. In the North and South America, this belt is largely on the continents and includes Andes and Cordilleran ranges. In the western part of the Pacific Ocean, they take form of Island arcs running through Aleutians, Japan and the Philippines.
Eurasian – Indonesian Belt: This starts from the west at Atlas Mountains in North Africa, through the near East and Iran to join Himalayas. Then it continue to South Eastern Asia into
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.
WIND
Is air in motion or is the movement of air from the region of high pressure to region of low pressure
ACTION OF WIND
This is more affected in the arid region especially desert than in humidity areas. Even in desert is found that wind action is more effective in hot desert than in cold desert. This is because of the following reasons (wind is in air motion)
A lot of loose and unconsolidated dry masses of sand and gravel that can be easily acted upon by wind. Mechanical weathering can take place hence exfoliation
There is absence of vegetation cover in most areas
There are very strong tropical storms within the desert
In hot desert because the air molecules expand so wind increase.
ARIDITY :
This refers to the state of the land being deficient in moisture leading to scarcity vegetation
These areas that receive less than 250mm of rainfall
A desert is therefore an arid area with sparse vegetation the rainfall in such area is very low and unreliable
Depression is the area where pressure is low.
THREE TYPES OF DESERT
Sand desert
Rock desert
Stony desert
SAND DESERT
Known as erg in the Sahara desert the surface of this desert is covered by mostly in large quantity of sand that are product of wind deposition.
STONY DESERT.
Known as reg in Algeria and Serir in Libya and Egypt.
-The stone desert surface is covered by angular boulders, gravel and pebbles.
ROCK DESERT.
Known as Hamada in the Sahara desert. Its surface is made up of barely rocks.
Scarcity in vegetation results in exposure of the desert surface to the agent of some process like;
Erosion
Transportation
Deposition
WIND EROSION.
Wind erosion in desert involves three processes namely.
Abrasion.
It is the mechanical/frictional erosion that is caused by the materials such as course particles that are carried down by wind.
It is done by hitting, grinding, scraping and polishing of the rock surface.
Deflation.
Is the blowing away of any unconsolidated materials like dust and fine particles. This is influenced by the nature of desert landscape, velocity and energy of the ocean currents.
Attrition.
Is wearing down of the wind borne materials as they collide against each other. They also rub or hit against rock forces in their path.
WIND TRANSPORTATION
This refers to the moving of material from one place to another by blowing wind.The movement of particles is determined by several factor like: Strongness of wind-usually over 20km/hr,turbulent from a constant direction,blow steadily for a length period of time.Wind transportation involve three processes namely.
Traction:This involves dragging or rolling of large pieces of materials such as pebble Saltation:Is process in which smaller pieces are carried while bouncing on the ground or on the surface.
Suspension: The process whereby very fine and light particles like silt or dust are transported while carried in suspension.
EROSIONAL FEATURES:
ROCK PEDASTALS.
These are tower like structure composed of alternate layers of soft and hard rock produced due to wind abrasion. Examples, found in Saudi Arabia, Tibet Mountain of the central Sahara.
It is made up of heterogeneous rocks of different resistances.
ZEUGEN
These are ridges consisted of layer of hard and soft rocks overlying vertically downwards.
They are formed in areas where the rock layer i.e. horizontally and are characterized by joints.
Weathering opens the joints and wind abrasion then continues the work of weathering leading to the formation of furrows and zeugen.
Illustration:
YARDANG
Are the ridges consisted of hard and resistant rock standing either vertically at an angle and vary in height from 15m but having length up to 100m.
Or
They are elongated rock ridges of vertically or nearly vertical layer of resistant rock separated by soft layers.
They run parallel to the direction of prevailing wind of abrasion.
The softer rock layers are easily worn out than the hard rock layers to form furrows and ridges. Example: Atacama Desert – South America.
Example: Salah-central Algeria,East of the Nile-The silsila gap.
BLOW OUT (DEFLATION HOLLOW, PANS)
These are hallows produced by wind deflation. Shallow depressions in outcrop of the weak rocks. They are deepening by wind deflation and some originated in faulted rocks. When those hollows are filled with water they are called oases or swamp.
Example:Kalahari,Near Tsane in Botswana,NW at Upington in South Africa etc.
INSELBERGS
They are residual hills consisted of land and resistant rock left standing on the surface often the rest part of the earth has been eroded.
– When inselbergs are smooth they are called boarnads.
They are characterized by a lot of joints.
DESERT PAVEMENTS.
These are the horizontal areas of bare, polished rock formed by the scoring action of grains of quarts. – Flatter in shape (escarpment)
VENTIFACT (DRAIKANTER).
These are heavier rock blocks pebbles left behind after wind has sorted and carried away all materials.
FEATURES DUE TO WIND (AEOLIAN) DEPOSITION.
The materials transported by the wind form different feature after deposition.
Features formed are like dunes (bar khans and seifs), loess and ripples.
SAND DUNES.
Hills of sand deposited by wind in the desert. Influenced by the extent of vegetation cover, the size of sand particles, amount of the materials and the velocity of the cover
Barchans/bar khans.
Crescent – shaped and lying at right angle to the prevailing wind horns pointing downwards
Eddies (an abrasion process) type of wind.
Seif dunes.
(Seif dunes) they are sometimes called longitudinal dunes. They are long narrow ridges of sand which lie parallel to the direction of the wind. They occur in the small scale in sand areas
LOESS.
Is an accumulation of sand that has been carried and deposited beyond the desert limits. Loess leads to the formation of fertile soil. Example can be found in China.
RIPPLES.
They are the smallest wave structure, sometimes less than centimeter high. They are commonly found between dunes.
Why are desert found in the western part of the continents?
Desert on the western side of continents are there because cold currents exist off the western side continents. Winds blowing over these currents lose their moisture over the sea and are dry by the time they get to land.
Due to prevailing winds. And that both continents have high mountain ranges on the west side. Air coming from the mountains (causing the moisture to condense out) and that leaves a rain shadow on the eastern side.
Due to their location, first being in the sub tropics places them in an area prone to lots of high pressure year round. High pressure discourages cloud development and precipitation being on the western of the continent, blocks humid air masses from reaching them.
GLACIATIONS
It appears that roughly every 200 – 250 million years in the earth’s history, there have been major periods of ice activity. Of these the most common (recent) and significant occurred during the Pleistocene period of the quaternary area.
In the two million years since the onset of the quaternary, there have been fluctuation in goods temperature of between 50C which have led to cold phases (glaciers) and warm phases (inter glaciers)
CAUSES OF ICE AGE/ THEORIES
-Variation in support activity may increase or decrease the radiation coming on earth.
-Injection of volcanic dust into the atmosphere can reflect and absorb radiation from the sun changes in atmospheric carbon dioxide gas could concentrate the green house effects (absence of carbon dioxide.
-The movements of Planets either into colder latitudes or at constructive margins where there is an increase in altitude could lead to an overall drop in world land temperature (high latitude low isolation.
-Changes in ocean currents or jet streams.
-Changes in atmospheric carbon dioxide gas could concentrate the green house effect
SNOW ACCUMULATION AND ICE FORMATION:
-As the climate gets colder more precipitation is likely to be in the form of snow in the winter and there is less time for that snow to melt in the shorter summer.
-If the climate continuous to deteriorate, snow will be falling throughout the year forming a permanent snowline. (The level above which snow will lie throughout the year).
-In the northern hemisphere the snow line is at a lower altitude on north facing slope and these receive less isolation (sun rays) than south facing slopes.
-Where snow collect in hollows it becomes compressed by weight of subsequent falls and gradually developed into more compact, dense form called firm or nerve.
.Firm is compacted snow which has experienced one winter freezing and survived for summer’s
melting.
-It is composed of randomly oriented ice crystals separated by air passed.
-In the temperature latitudes such as in the Alps, summer melt water percolates into the firn only to freeze either at night or during the following winter forming an increasing dense mass.
-Air is progressively squeezed out and after 20-40 years the firm will have turned into solid ice.
-This same process may take several hundreds of years in Antarctica and Greenland where there is no summer melting.
-Once has formed it may begin to flow downhill under the force of gravity as glacier.
GLACIER AN ICE MASSES:
-Glaciers may be classified according to size and shape characteristic which are relatively easily to identify by field observation. These are,
LANDFORMS PRODUCED BY GLACIAL EROSION.
Niche glaciers.
-Very small and occupy hollows and gulley on north facing slopes in the northern hemisphere
Corrie or cirque.(highland glacial erosion features.
-Although larger than niche glaciers are smaller masses of ice occupying arm – chair shaped hollows in mountains. They often over pill from their hollows to feed valley glaciers.
-These are armchair – shaped hollows with a steep back wall and a rock basin. They are known as corries in Scotland.
Arêtes.(highland glacial erosion features)
-When two adjacent cirque erode backward or sideways toward each other the previously rounded landscape is Transformed into a narrow, rock steep side ridges called an arête, example Alps in Switzerland.
Pyramidal peak.
-If there are three or more cirques all side of a mountain a pyramidal peak or horn may be formed.
-This feature has steep side and several arête radiating from the central peaks.
-When either cirque is combined together can form pyramidal peak.
Truncated spurs
-Formed by meanders in the low lands, where by the rate of erosion has decreased and the rocks are hard and at the end form alluvial fans.
-Spurs whose ends have planed off due to erosion on the process of straightening the valley as it moves down the valley (highland glacial erosion feature).
Crag and tail (lowland glacier erosion features)
-This consists of a larger mass of resistant rock or crag (e.g. Basaltic rock crag upon which Eden burgh has been built).
-High pressure where is small area and low pressure is large area.
Roche mountaineer. (Lowland glacier erosion feature)-
-An outcrop of resistant rock which rise above the plain smoothed by ice on the upstream by abrasion and plucking processes. This feature also occurs in glaciated highlands. An outcrop of resistant rock smoothed by a glacier on the upstream side into a gentle slope. On the downstream side the glacier erodes by plucking to give steep and jagged (rugged) slope (lee).
Example: Mobuku Valley in the Ruwenzori mountains,Yosemite National Park in California,on the slope south of Mawaza along Mt.Kilimanjaro.
U-shaped valley/glacial trough. (Highland erosion features)
-It is a steeply sided flat-bottomed wide glacial valley. Develop from a river valley in which glacier had covered. Some contain features formed by both glacial erosion and deposition.
At initial stage the valley occupied the V- shaped valley but because of continuous glacier erosive activities. The valley was more enlarged by being more deepened and widened becoming more opened and known as U-shaped valley.
Hanging valley.
-It is a tributary valley that ends abruptly above the floor of a U-shaped valley and separated from it by almost a vertical slope.
-The rate of erosion is much greater at the main glacier valley than on the tributary valley, after glacier have retreated the floor of the main glacier valley lies far below than the floor of a tributary valley making the tributary valley to hang by ending a abruptly above the valley.
-A river occupying a hanging valley will fall more abruptly into the main valley to form waterfalls and produce alluvial fans.
Rock basin
(highland erosion features)
– It is an irregular depression of the floor of glacial valley formed by unequal glacier upon the bedrock.
This develops when weight and thickness of glaciers increase after two glacial have joined together.
After glacier melts, rock basin becomes the site of lake. These are known as rock basin lakes.
Ribbon lake
(Finger Lake or Trough Lake).
Is a lake that occupies an elongated trough or hollow excavated by ice on the floor of a u-shaped valley E.g. lake Michelson near Mt. Kenya (Highland erosion features)
Fiord. (Highland erosion feature)
It is a long, narrow, deep in let depression steeply sided into the sea. Fiords were formed when glaciers make the way to the sea.
Most of the fiords occupied by deep sea water after the coastal land submerge due to ice melting forming natural harbours e.g. the also fiord of Norway.
Ice eroded plain. (Lowland glacier erosion)
It is an extensive and almost level lowland area of bare rocks .It was once covered by an ice sheet which smoothed the topography and produced large area of bare rocks.
GLACIER TRANSPORTATION AND DEPOSITION
Glacier movement can also result into the formation of depositional features such as;
Moraines. (Highland (alpine) deposition features) unsorted materials.
Are the unsorted fragments of different size and shape that have been eroded, transported by glacier and then deposited in ridges within the glacial valley.
Types of moraines
based on area within the glacier valleys where materials have been deposited;
a) Ground moraines
– Formed at the bottom of glacier valley.
b) Medial moraines– Formed at the point where two glacial valleys meet
Adjacent lateral moraines joined and are carried as a single long ridge of till.
c) Lateral moraine
– Formed along side of the glacial valley. (Ridge like piles of till along the sides of glacier).
d) Terminal moraine– Occurs at the end of glacial valley as the materials had been accumulated.
Terminal moraines are built up when glacier is stationary.
Materials of terminal moraines can be carried down the valley by melt water and deposited to form a feature known as outwash plain.
e) Recessional moraines
– The end moraines built while the glacier is retreating. (A series of roughly parallel terminal moraines that make the step by step retreat of the glacier).
Boulder clay plain. (Lowland glacial deposition)
(Till plain)- Is an extensive lowland (plain) area consisting of clays and boulders deposited randomly by ice sheet and burying vast area of land.
Erratics
are large boulders made of rock, different from that of the region where they are deposited
Drumlins
(unsorted materials) (lowland glacier)
They are elongated oval shaped hill that are made of clay and boulders as they were deposited irregular on a till plain (boulder plain). They occur in groups and aligned in one another.
Eskers (lowland) (sorted fluvial – glacial material)
Long, steep sided ridge of course sands and gravels.
Formed when ice remain stationary for long time. Streams form permanent sub glacial in which materials consolidate and compact if ice melts the materials are left as ridges which referred to eskers.
Kames
(lowland)
Is an irregular mound or hill (mass) of stratified materials (sand and gravel)
Kames vary greatly in shape and size and occur in isolation or large groups. They form as ice deposited materials randomly.
Out wash plain
(lowland)
It is a wide gently sloping low lying land of gravel and sand at the end of an ice-sheet.
Out wash plain is usually found after boulder clay plain.
Value/importance/significance of glaciated land escapes to human being.
Some glaciated landscape like that of boulder clay plain and others are good for agriculture.(fertile)e.g. Dairy belt in U.S.A also crop cultivation in old glacier lakes e.g. wheat cultivation in Canadian prairies.
Hanging valleys are suitable for HEP generation. E.g. Norway, Sweden and Switzerland produce great proportional of hydro electricity by utilizing waterfalls of hanging valleys.
Glaciated landscapes provide attractive scenery also the glaciated highlands and peaks e.g. Mt Kenya and Kilimanjaro attract tourists.
Many glaciated valleys are used as grazing land as they contain good pastures. They are used for animal grazing main in summer season .e.g. In the Alps in Europe.
Fiords form natural harbors e.g. Oslo ford in Norway and also fishing-grounds.
Glaciated landscape contains a number of lakes which are used for navigation e.g. great lakes in
N. America.
Melting of glaciers give rise to rivers. The rivers can be utilized for domestic and industrial purposes.
Disadvantages of glaciated landscape
The boulder clay plain in some regions, have produced a mainly landscape which have little or no value to agriculture e.g. central Ireland.
Many out wash plains contain infertile sands which give rise to extensive areas of waste land.
WAVE ACTION AND THE FEATURES IT PRODUCES.
-Is the horizontal movement of ocean water, in the movement process it does the following three main works: These are:-erosion, transportation and deposition
-Waves should not be confused with tides which are the vertical movement of sea water.
MOVEMENT ASSOCIATED WITH WAVES.
Swash:
-The movement of sea water towards the beach is known as swash.
Back wash:
-The movement of water from the beach back to the ocean after the breaking waves.
Wave break
-Is the split of the wave when it releases its energy on the coast.
Wave erosion
– This takes place along shore (coast). It is determined by the nature of the rock and strength of the waves.
WAVE EROSION PROCESSES CAN BE DIVIDED AS FOLLOWS:
Corrosive action:
-These kinds of erosion taking place when the rock fragments (particles) carried the waves are used as tools of erosion. They usually bang and cut the bare of the cliffs
Hydraulic action:
-This occurs when water is thrown against the cliff. The air pressure expands the cracks and so the rocks are broken into smaller pieces.
Attrition:
-This is the breaking down of the materials carried by waves when they crash among themselves to form smaller particles.
Chemical Solvent Action:
-This occurs in the coast consisting of limestone rocks. The carbon dioxide in the water will change the insoluble calcium carbonate (caco3) (in limestone) to calcium Hydrogen Carbonate Ca(HCO3)2 which is easily removed.
*Cliff: Raised land facing the sea going in land (into the land). It is vertical.
Wave Erosion leads to the formation of the following features
a) Cave:
-This is a chamber of a big hole formed by water when soft rock is removed by the waves usually soft rock materials are washed away by strong waves and taken to the ocean in the same way – is a natural chamber extending into the head land or the cliff along the coastline. The weakness as opened up by wave abrasion and hydraulic action.
b) Stack:
-This is a pillar which remains when the roof of arch collapses. It is a pillar which is separated by water from the rest of the dry land.
c) Arch;
-This is a feature which is formed when two waves in opposite are joined usually the top of this hole is roofed by a hard rock.
->Is a curved opening through the head land resulting from a head land eroded right through from one side cave to the other side of the head land.
d) Headland:
Refers to a high promontory with a steep faces, projecting into the sea or a lake and which is mostly formed as less resistant rocks have under gone erosion.
->Is a piece of land that grows sea wards. Hard rock bands less eroded.
Head land
e) Bay:-
-Refer to curved indentation of the sea into the land which is formed as a result of the removal of less resistant rock.
-Is a narrow sea in let formed along the coast of alternative rock hardness, the soft rock band easily eroded and produce sea inlet.
f) Geo;
Is a long narrow sea inlet which penetrates the cliff formed when the roof of a blow hole collapses.
g) Blow hole; – Is a hole which extended from the cave to the surface of the upper part of cliff formed due to abrasion and hydraulic action against the cliff with a cave, makes the hole of the cave to be more enlarged and reach the top.
h) Stump;
Is a reduced stack in height under water, usually visible at low tides.
-Continuous wave action can make the stack get lowered in height and completely immerses in water.
i) Cliff.
Is a high more or less vertical walled rock surface which borders the sea.
Formation of a cliff starts with the development of a notch along the coastline. (Notch is a hole formed on the rock face of the coastline due to continuous beating of waves).
Due to continuous beating the notch is expanded and finally results to the occurrence of the outgrowth rock known as cliff.
Formation of cliff depends on nature of the rock, stratification and presence of joints.
a) Waves attack a steep slope/coast.
b) A notch forms at the high tide level mark
c) Over hanging block collapses and cliff forms.
-Waves attack new cliff base to form an overhanging cliff.
j) Wave cut platform– Is a fairly that part of the shore which is formed by wave erosion as the cliff line retreats inland. Cliff being more steep or vertical may collapse seawards due to denudation thus mass of the collapsed cliff accumulate over a wider area in the ocean to produce wave cut plat form e.g. found in the west coast of Norway.
WAVE DEPOSITION
-The eroded material are transported and deposited on the shore along the coast. The deposited materials is those that have been eroded from the coast its self or from the rivers.
The following are the wave deposited features;
Beach;-This is the accumulation of sand, pebbles, shingle and mud on shore along the coast. The material decrease seaward (from the coast to the sea). The arrangement follows this pattern. Boulders, Shingles, pebbles, sand and mud. (Smooth surface).
Formed by constructive waves on the gentle sloping surface between high and low water level.
(Transportation of materials consist of swash and back swash (long shore drift))
Example Mombasa in Kenya,Tunza Beach in Mwanza,In Dar-es-salaam Kawe , Kigamboni and Coco beach.
Bar – A bar is a ridge of material, usually sand which lies parallel to the coast.
-This is a narrow ridge of sand and shingle formed in the sea. It is parallel to the coast line.
-Unlike a spit, a bar is not attached to the land.
TYPES OF BARS
a) Tombolo
b) Bay Bar
c) Off-shore bars.
a) Tombolo
Tombolo is a type of bar which connects the land and an island. Occurs when a bar joins an island to the main land.
Accumulation of sand where one end attaches coastal and the other end is attached to the island.
Different between an estuary and a Tombolo.
-Sometimes a spit can become curved/ hooked when formed on hard land and when waves meet the end obliquely.
b) Bay bar
– Is the bar that runs across the bay.
a) Off-shore bar
-Accumulation of sand deposited on the gentle sloping sea bed (off shore zone) where sand is thrown up by waves breaking some distance from the coast.
Spit – This is a narrow tongue of sand and shingles joined to the land and projecting into the sea. Example; hooked spit in Namibia.
– Is a very long and narrow ridge of pebbles and sand joined to the mainland at one end and terminating into the sea on the other end.
Waves meet the end oblique.Example: Bagamoyo in Northern Dar es salaam in Tanzania,Medjerda delta in Tunisia etc.
Mud-Flat
Deposits of mud in the base of the ocean. They can be reclaimed (modified) and become very fertile.
-Deposit of fine soil and silt in the gently sloping coast especially in the bars/estuarine. Example Lamu mud flat along East Africa Coast at the mouth of river Rufiji etc.
Lagoon
Is a shallow enclosed amount of water which is usually caused by deposition of materials at shallow waters of the ocean.
-Is a shallow area of coastal water completely or partly separated from the open sea by sand banks (bars or spits).
E.g Benin (Dahomey, Nokone and heme to the east of Nigeria.)
CUSPATE FOR ELAND
Is a large triangular deposit of sand or shingle which is terminating sea wards. It is formed as two(2) spits which form towards each other eventually merge.
Example:Tonga around L.Albert,Cape canaveral in Florida,The Darss on the Coast of Mecklenburg,East Germany etc
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