SECOND TERM GEOGRAPHY SS2 E-NOTE.docx

  • WEEK ONE - Action of Wind in Desert Areas (SS2 GEOGHRAPHY E-NOTE)

Introduction:

Wind is a dominant element in all desert environment. Desert are associated with dryness caused by low rainfall, high temperature, cold current and high evaporation. On the globe, deserts are confined within 15º to 30º north and south of the equator. The action of wind has resulted in both erosional and depositional features in desert areas.

Characteristics of deserts

  1. Extreme temperatures
  2. Low rainfall
  3. High evaporation
  4. Absence of vegetation cover

Types of deserts

  1. Erg or sandy deserts: they are made up of sand
  2. Hamada or rocky deserts: they are made up rocks
  3. Reg and stony deserts: they are made of pebbles and gravel
  4. Badlands: these are deserts highly eroded by wind
  5. Mountain desert: these are deserts on mountainous areas
  • A DESERT AREA
  • Processes of Wind Erosion
  1. Deflation: it involves lifting and blowing away of loose sand. It usually result in the lowering of the land surface into large depressions called depression hollows.
  2. Abrasion or corrasion: this process involve the wearing away of exposed rock surfaces by sand particles carried by strong wind. Corrasion is most effective at or near the base of the rocks, where the wind is strongest.

3. Attrition: this process involves wind-borne rock particles colliding with each other and with obstacles, and wearing away each other, to become reduced and well-rounded.

  • Features of Wind erosion
  1. Yardang: they are tabular masses of rocks with alternate vertical layers of hard and soft rocks, which have been worn down into ridge and furrow landscapes. They are formed as wind abrasion wears off the soft rock to form long narrow corridors leaving ridges of hard rocks.

2. Zeugen: these are tabular masses of rocks having alternate horizontal layers of hard and soft rocks. The presence of joints in the rocks due to mechanical weathering allow wind to further wear the rocks, into a ridge and furrow landscape.

3. Rock Pedestal: these are mushroom shaped features of wind erosion, having alternate layer of soft and hard rocks. Abrasion wears back the soft layer, while the hard layer protrudes forming an irregular shape. They look like pillars having narrow base or neck with broad top or head. They are common in the Sahara, e.g Devil’s Rock north of Agadez in Niger Republic.

4. Inselberg: It is a flat topped or dome-shaped isolated residual hill which rises steeply above the surrounding desert floor. It is composed of crystalline rocks like granite and gneiss, believed to be remnant of a former plateau. Inselbergs are found in the northern parts of Nigeria.

5. Messa and Buttes: a Messa is a flat resistant table-like rock mass underlain by soft rock. The resistant top protects the base from erosion by rain or wind, leading to steep sides. Persistent denudation can reduce a Messa to an isolated flat-topped hill called a Buttes.

6. Deflation hollow: it is a large depression in the desert floor, formed by wind abrasion. As the depression deepens further it may reach the water table resulting in an Oasis. An example is the Qattara Depression in Egypt covering 15000sq Km, and 130m below sea level.

7. Ventifacts: they range from small stones to large boulders, because of their size are not blown away, but are faceted and wind-polished. A one faced ventifact (dreinkanters) denotes wind is constant in only one direction, while a three faced ventifact (dreinkanter) implies wind blows from different directions.

  • Features of Wind Deposition
  1. Dunes: they are formed by the accumulation of sand into hills or heaps, and shaped by wind. This has given rise to two types of sand dunes:

a. Barchan: They are formed as rock mass impedes the movement of wind, allowing it to drop its load around it. The sand accumulate over time to form a crescent or moon-shape mass. They are convex on the windward side and concave on the leeward side, having horns of about 15-30m long pointing in the direction of the wind.

b. Seif or longitudinal dunes: they appear like swords, having long narrow ridges, spanning hundreds of kilometers. They are formed when wind-blown sand accumulate parallel to the prevailing wind. They may reach a height of 60m. They can be found in the Sahara and Qattara Depression.

2. Loess: these are usually loose and fine rock particles which are carried by the wind and deposited outside the desert. The accumulation of these material result in loess. They are usually loamy, fertile and porous.

  • WEEK TWO - ACTION OF GLACIER

Introduction:

A glacier is a persistent body of ice, constantly moving under the influence of gravity. This movement down a valley is called GLACIATION, and it can result in erosion, transportation and deposition of rock materials, leading to the formation of several features. The activities of glacier is confined to mountainous places in polar and temperate regions.

  • Processes of Glacier Erosion

The activities of glacier is characterized by the following processes:

  1. Sapping: it refers to the breaking up of rocks due to alternate freezing and thawing at the bottom of the ice sheet and at the sides of the valley.
  2. Plucking: this process involves the tearing of blocks of rocks, after they have become frozen at the sides and bottom of a glacier. It usually create a jagged surface.

c. Abrasion: it refers to how rocks contained in the sheets of moving ice rub on and wear away as they come in contact with the slope.

  • Features of Glacier Erosion in Highland Areas
  1. Striations: these are scratches or marks left on the rock surface by rocks fragments embedded in moving sheets of ice.
  2. Corries or cirques: these are deep and rounded depressions formed due to continuous erosion of the surface of the slope by ice. Here, plucking is the dominant process. As the ice moves down slope it leaves behind a corrie lake.

3. Arete: it refers to situation where two corries acting on opposite sides of a mountain lead to the formation of a knife-edge ridge called arête.

4. Pyramid peaks: these are formed by three or more corries acting on the same mountain with deep cut-backs. It result in the formation of a pinnacle shape called pyramid peak.

5. Bergschund: this is a deep vertical crack at the head of the glacier, separating the lower part from the high part. It usually occur in summer, a good time when glacier begin to move out of corrier down the valley.

6. U-shaped valley or trough: it result from further erosion and widening of the valley by moving ice.

7. Moraines: these are pieces of rocks broken down by frost action, and brought down the valley by the moving ice. They exist as lateral, medial and terminal moraines.

  • Features of Glacier Erosion in Lowland Area
  1. Roche moutonne: this refers to a resistant rock mass, which has been smoothened by moving ice sheet. The upstream side is smooth due to abrasion, while the down stream side is rough due to plucking.
  2. Crag and Tail: it is a mass of resistant rock, standing in the way of a glacier. It protects the leeward side from erosion, while the other side is smoothened into a gentle sloping tail by the moving ice.
  • Features of Glacier Deposition in Lowlands
  1. Boulder Clay: this is a collection of sand and clay. It contains stones of various size and shape brought down as moraines of glacier.
  2. Drumlins: they are swarms of oval, elongated whale-back hummocks, composed of boulder clay. The lying parallel to the direction of the flow of ice.

3. Eskers: these are long, narrow and winding ridges of sand and gravel, deposited by melted ice streams. They are porous and numerous.

4. Terminal moraines: these are boulders found at the edge of the ice sheet. They usually form a large debris deposited at the edge of the ice sheet.

5. Outwash plain: this is the area beyond the moraines, composed of sand and gravel, washed down the mountain and deposited to form an extensive area.

  • ACTION OF WAVES (IN COASTLANDS)

Introduction:

The activities of waves is confined to the coastal environment of seas and oceans. Its activities include erosion, transportation and deposition of materials. The rate of marine erosion depends on the nature of rocks, the amount of exposed rocks, and the strength of tides and currents, and human interference in coastal protection.

  • Processes in Wave Erosion

1. Corrasion or abrasion: this is the wearing down of the base of the cliff by waves.

2. Attrition: this is the breaking down of rock fragments into smaller particles as they are thrown against the surface of the cliff, and as they collide with each other.

3. Hydraulic action: it refers to high velocity waves which force themselves into cracks and cavities in the base of the cliff under pressure and enlarge the cracks.

4. Solvent action: it refers to the breaking down of rock materials, e.g limestone, by chemical action of the sea.

  • FEATURES PRODUCED BY WAVE EROSION

1. Capes and Bays

Characteristics:

  1. They are features of wave erosion
  2. They are made of hard and soft rocks

Mode of Formation

They are formed as a result of the action of waves on rocks of varying resistance. Thus, the coast is eroded irregularly; soft rocks are worn out to form bays (inlet), while the hard rocks form capes (headlands).

2. Cliff

Characteristics:

  1. They are steep rocks

Mode of formation

They are formed due to the action of powerful waves acting on the base of headland rocks, cutting it backwards, and leaving a protruding top.

3. Coastal cave

Characteristic:

  1. It is a feature of marine erosion
  2. It may contain blow-holes or geo

Mode of formation

It is formed by wave erosion when soft rocks are greatly eroded. As wave continues to batter the point of weakness, the rocks are removed at greater rate, and the hollow created is widened and deepened. More forceful impact on the hollow will lead to the formation of a cave.

4. Arch: it is formed when two caves approach each other from either side of the headland, and they meet to form an arch.

5. stump: it is a small portion of the rock left standing, a little above the sea-level, after a stack must have been seriously eroded.

6. Stacks: it is formed by wave erosion. As waves attack both sides of a headland with caves on both sides, further erosion of the caves leads to collapse of the roof of the cave. The seaward part of the headland is left standing.

7. Geo: it is a narrow hole which has cut through a cliff due to the collapse of the cliff.

8. Gloup or Blow-hole: it formed as a result of erosion on coastal cliff. This is possible due to less resistant rock at the base of the cliff having a cave. The cave is further enlarged due to vertical joint present at the roof of the cave. The joints are expanded by hydraulic action of the waves, causing loose blocks to fall into the cave. This process may force water , spray or air out of a hole called blown-hole.

  • Features of Coastal Deposition
  1. Beaches: it is the area of sloping ground along a coast, between the highest water-mark and the lowest water-mark. It is an accumulation of sand, shingle or mud. Beaches are various types, e.g. sand beach, shingle beach etc.

2. Spits: they are referred to as ridges of sand and gravel, or tongue-like features made up of alluvium deposit, formed across the entrance to a bay or coastal inlet. An example is the Spit across the mouth of River Senegal.

3. Sand Bars

Mode of formation:

These are sand deposits at the shallow water area, lying parallel to the coast. The sand and other materials accumulates each time there is a backwash, encouraged by the low current. With time the accumulated sand result in a bar.

Characteristics of Sand bar:

  1. They lie parallel to the shore
  2. It is covered at high tide and exposed at low tide
  3. The waves do open narrow channels in it.

4. Marine dunes and dune belts: these are large mounds of coastal sand formed by forceful shore winds. Accumulation of several dunes will later stretch into a dune belt.

  • Types of Coasts

A coast is the land bordering a nearby ocean or sea.

A coastline or sea-shore is the area where the land meets the sea or ocean. They are categorized based on the structure of the land, whether it is hilly or mountainous, and whether it is raised or depressed by erosional forces of the sea. Below are the types of oceans:

  1. of submergence: these coastlines are formed due to the sinking of the land or rise of the sea. E.g ria coastline, fiord coastlines, estuary coastline and Dalmatian coastline.
  2. Coastline of emergence: these coastlines are formed as a result of the uplift of the land or fall in the level of the sea. E.g uplift lowland coast and emergent upland coast.
  • Coastlines of Submergence
  1. Ria coast: these are long narrow branching inlets, which are separated by narrow headlands. They are formed when sea-level rises to submerge the lower part of a narrow Coastline valley. They are deep; for example those found along the coast of Gambia to Sierra Leone in West Africa, Northwest of France etc.
  2. Fiord coast: these are glaciated U-shaped troughs. They are shallow due to the effects of glacier on the land. Examples are coast of Norway, Alaska and Southern Chile.

3. Dalmatian or longitudinal coast: these coast are found in places where mountains run parallel with the coast. Submergence of the coast result in long narrow inlets, with chains of islands standing parallel to the coast. They are not suitable for port development. E.g. coast of Yugoslavia etc.

4. Estuary coasts: these are formed as lowland areas at the mouth of rivers submerge or collapse to form a funnel-like structure. E.g. coasts of London, Hamburg and Buenos. These are sites of great seaports.

  • Coastlines of Emergence
  1. Uplift lowland coast: this is formed by the uplift of the continental shelf, having a smooth, gentle-sloping coastal lowland. The offshore water is shallow and has salty marshes e.g. South-eastern USA
  2. Emergent upland coast: this is formed due to faulting and earth movement, leading to the rise of the coast lands. The coast is straight, steep and has deeper shore water. For example, coast of Scotland.
  • CLIMATIC ELEMENTS AND FACTORS AFFECTING THEM

Rainfall:

Rainfall can be defined as water droplets, which have condensed from atmospheric water vapour and then precipitated, and fall from the cloud due to gravity.

Rainfall is the most important form of precipitation. It is a major component of water cycle, and responsible for depositing most of the fresh water on the earth. On maps places having the same amount of average rainfall are joined with a line called Isoyet.

  • Other Forms of Precipitation

1. Snow: it is formed as water vapour condenses in the atmosphere at temperature below 0°C, to form ice crystals.

2. Dew: it is formed when condensation takes place on the ground or on surfaces like leaves, buildings or vehicles.

3. Frost: this is formed when water droplets in the surrounding condensed into ice crystals at temperature below 0ºC.

4. Hail: it is formed when water droplets at great height condense and rain as ice crystals.

5. Fog: this is formed when water vapour condenses around dust and gas particles in the air, usually above the sea or near the ground. It usually cause poor visibility.

6. Mist: it is similar to fog, only that the water droplets are smaller in size

  • Types of Rainfall
  1. Convectional rainfall:

It is very common in tropical and temperate environment.

Mode of formation:

They are formed as the sun heats the ground and warm air rises, which then cools and condense to form clouds. As condensation increases, large Cumulonimbus clouds are formed, which result in rain.

Characteristics:

  1. It is torrential or heavy rainfall
  2. It is accompanied by lightening and thunderstorm.
  3. The cloud associated with it is called as cumulonimbus

B. Orographic or Relief rainfall:

Mode of formation

Moist air is caused to rise above a mountain on the windward side. On rising, the air expands and cools, with humidity rising. The air becomes saturated with water vapour, which condenses to a point where it starts raining.

Characteristics:

  1. It is associated with mountainous region
  2. There is rainfall on the windward side and little or no rainfall on the leeward.
  3. It is characterized by ascending and descending wind.

C. Cyclonic or Frontal Rainfall:

Mode of formation

It occurs when two air masses of different temperatures meet. The warm air and cool air do not mix due to their different densities. So, the warm air rises over the cool air becomes cool too, which result in a front. This creates cloud and eventually produces rain.

Characteristics:

  1. It characterized by fronts and weather system in mid-latitudes.
  2. It lasts for greater duration than convectional rainfall.
  3. It covers a larger area
  4. It moves from west to the east in the northern hemisphere, and vice-versa for the south.
  • Temperature

Definition:

Temperature can be defined as the degree of hotness or coldness of a place.

Factors Affecting Temperatures

1. Latitude: this is the location of a place north or south of the equator. Places in tropical latitude experience higher temperatures than places in temperate latitude, while places toward the poles experience a much lower temperature.

2. Altitude: this is the height of a place above sea level. Places nearer to the earth surface are warmer than those at higher altitude. This is so because, temperature decreases by 0.6°C with every 100meters accent above sea level.

3. Distance from the sea: land surfaces farther from the sea experience warmer temperature than those closer to the sea. The sea cools the coastal lands in summer and warms them in winter. This influence of the sea is stronger for lands closer to it than those farther.

4. Prevailing winds: these are dominant winds of particular regions. They are either cold or warm, depending on the season. They affect temperature of adjacent places by losing their heat or coldness, as they travel.

Note: on a map places having equal average temperature are joined with a line called Isotherm.

  • Lapse Rate

It is defined as the rate of decrease in temperature as one ascends into the atmosphere. This implies there is a 0.65ºC drop in temperature for every 100metres ascent, Or 6.5ºC decrease in temperature for every 1000metres ascent.

  • Temperature Inversion

It can be defined as the increase in temperature as one ascends into the atmosphere. It is the opposite of lapse rate. This phenomenon is common in places such as, above the surface of the sea and in valleys surrounded or enclosed by mountains.

  • WIND

Definition:

This can be defined as air in motion, having speed and direction.

  • Factors Affecting Wind
  1. Rotation of the earth: the direction of wind across the earth’s surface is influenced by the movement of the earth. In the northern hemisphere it is deflected to the right, and in the southern hemisphere to the left. This movement is refered to as Ferrel’s Law of Deflection.
  2. Temperature: it affects wind in the sense that when air is heated it expands and rises, giving room for surrounding cold air to slip in to replace the rising air.

3. Pressure: when heated air rises its pressure decreases, while the cold air around maintain a higher pressure. This differential in pressure makes wind blow from the low pressure belts to high pressure belts.

  • PRESSURE

Definition: it is defined as the force exerted on the earth’s surface and on objects by air.

On maps, places with equal amount of atmosphere pressure are joined by a line called Isobars.

  • Factors Affecting Pressure
  1. Altitude: pressure decreases as altitude increases and vice versa.
  2. Temperature: increase in temperature of air will bring a decrease on its pressure and vice versa.

3. Wind: wind usually blow from a region of high pressure to a region of low pressure.

4. Rotation of the earth: rotation of the create differences in pressure, leading to the deflection of wind to the right in northern hemisphere and left in the southern hemisphere.

  • Pressure Belts

Pressure Belts

  1. Doldrum or Equatorial low pressure belt
  2. Horse latitudes or sub-tropical high pressure belt
  3. Temperate low pressure belt
  4. Polar high pressure belt
  • Distribution of Pressure Belt
  1. Equatorial low pressure belt: it is found between 5º N and 5ºS of the equator. The pressure here is low due to intense heat.
  2. Horse latitudes or sub-tropical high pressure belt: it is found between 20º-30º north and south of the equator. Pressure is high and wind tend to diverge from here.

3. Temperate low or Mid-latitude low pressure belt: it is found between 30º-60º north and south of the equator. They are zones of convergence with cyclonic activities.

4. Polar high pressure belt: they are found in the polar regions and the winds shift with seasons.

  • Cloud Cover

Definition: cloud refers to condensed water vapour, suspended in the high atmosphere. Cloud cover on the other hand refers to the degree of cloudiness of the atmosphere of a place.

On maps, places with equal degree of cloudiness are joined by lines called ISONEPHS. Also, the amount of cloud in an area is measured with Oktas.

  • Classification and Types of Cloud

There are four classification of clouds:

  1. High clouds: these category of clouds has three subtypes- Cirrus, Cirrocumulus, and Cirrostratus. They are found within heights of (6000-12000)metres.
  2. Middle clouds: these category of clouds has two subtypes- Altocumulus, Altostratus. They are found within heights of about (2100-6000)metres.
  • Types of Cloud
  • Lower Cloud
  • Storm Cloud

c. Low clouds: these category of clouds has three subtypes- Stratocumulus, Stratus, and Nimbostratus. They are found at heights lower than 2100metres.

d. Clouds of great vertical extent: these category of cloud has two subtypes- Cumulus and Cumulonimbus. They are found within heights of 6000-9000metres.

  • Sunshine

Definition:

This is the amount of heat and the period in which sun-rays is received in a place.

Factors that affect Sunshine

The amount of sunshine received in a place is influenced majorly by the seasons experienced by the place. By extension seasons are influenced by the latitude of a place and the position of the earth during revolution.

On maps places having equal amount of sunshine are joined with lines called ISOHEL. Also, the duration of sunshine is measured with a sundial, and the minute/hourly sunshine of each day is measured using light metre.