The Dynamic-Earth And Consequence

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 C_a(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