CE Geography-A Summary

Section A-Land

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PART 1 - The land: Sculpture of the Earth’s surface

A.  Structure of the Earth and plate tectonics

1.  Structure of the Earth

a.  Core - made of nickel and iron.

b.  Mantle - made of iron and manganese.

c.  Crust - (i) oceanic crust made of sima (ii) continental crust made of sial.

2.  Lithosphere

a.  Crust plus upper mantle.

b.  It consists of (i) oceanic plates and (ii) continental plates.

3.  Plate tectonics and their movements

a.  Folds result from the compression of sedimentary rocks in colliding plate margins.

b.  Displacement of rocks on either side of a fracture is called a fault.

c.  Normal faults result from tension. Reverse faults result from compression.

d.  Plate margins are zones of instability.

e.  Margins of divergent plates are constructive as new crust forms.

f.    Margins of convergent plates are destructive as crust is destroyed.

g.  Margins of plates moving sideways past each other are neither destructive nor constructive.

h.  Formation of fold mountain involves sedimentation, collision of plates, subduction of margin and uplifting.

4.  System to show mountain building

5.  Landforms produced by plate movements

B.  Vulcanicity

1.  Vulcanicity

a.  This refers to the flow of magma into the crust, the emission of lava, gases and super-heated water at the surface and the landforms that these produce.

b.  Magma solidifies to form igneous rocks.

c.  Magma that solidifies in the crust is called an intrusion. It forms intrusive rocks.

d.  Magma that passes through the crust to the surface is called an extrusion. It forms extrusive rocks.

2.  Intrusive vulcanicity

a.  Batholith - a large mass of intrusive crystalline rock.

b.  Sill - an intrusion lying between bedding planes.

c.  Dyke - an intrusion cutting across the bedding planes.

3.  Extrusive vulcanicty

a.  Magma is extruded through a vent or a fissure.

b.  Vent extrusions often produce volcanoes.

c.  Fissure extrusion produce lava plateaus.

d.  The shape, height and base width of a volcano depends on the type of lava extruded.

e.  Extrusion through a vent is called a volcanic eruption. An eruption may be quiet or violent.

f.    The violent emission of super-heated water at intervals is called a geyser.

g.  The quiet and continuous emission of super-heated water is called a hot spring.

4.  Natural hazards of vulcanicity

Natural hazards associated with volcanic eruptions include earthquakes, burial under lava / ash, emission of poisonous gases, fire hazards, landslides / mudflows, tsunamis and floods.

C.  Rocks

1.  Igneous rocks

a.  The Earth’s crust is made of rocks which are composed of minerals.

b.  Igneous rocks are crystalline. Sedimentary rocks are non-crystalline.

c.  The main rock types in Hong Kong are igneous.

d.  The highest peaks are made of volcanic rock.

2.  Sedimentary rocks

a.  A sedimentary rock is composed of strata or layers. It is said to be stratified.

b.  A conglomerate is a sedimentary rock which contains large, rounded rock fragments.

c.  A breccia is a sedimentary rock which contains large angular rock fragments.

3.  Metamorphic rocks

A rock whose characteristics change through either heat or pressure or both is called a metamorphic rock.

4.  Classification of rocks

D.  Denudation

1.  Denudation

a.  Denudation refers to weathering, mass wasting, erosion and transportation.

b.  Weathering is of two types: mechanical (physical) which causes rocks to disintegrate, and chemical which causes rocks to decompose.

c.  The end product of weathering is regolith.

2.  Mechanical weathering

a.  It attacks bedding planes and joints.

b.  Sheeting - layers of rock splitting from a mass of rock through pressure release.

c.  Block disintegration - well-jointed rocks breaking up into blocks.

d.  Granular disintegration - rock break-up grain by grain.

e.  Exfoliation - when layers of rock peel off from boulders.

3.  Chemical weathering

a.  Takes place by the processes of solution, hydration, hydrolysis, oxidation and carbonation.

b.  Spheroidal weathering - chemical weathering of granite below the surface producing rounded boulders whose centres are unweathered, forming corestones.

c.  Clints, grikes, swallow holes are caused by chemical weathering of limestone.

4.  Biotic (biological) weathering

a.  The break-up of rocks by plants and animals.

b.  Most active in warm, humid climates.

5.  Mass wasting

a.  The movement of weathered material (including soil) downslope under the pull of gravity.

b.  It involves the processes of soil creep, rockfall, slide, slump and flow.

c.  It occurs when slopes are unstable.

d.  Mass wasting has caused several serious landslides in Hong Kong.

e.  Landslides in Hong Kong may be controlled or prevented by planting trees on the upper slopes, restricting building on steep slopes, building more and deeper storm drains and covering steep slopes with Chunam plaster.

6.  Surface wash

a.  It consists of the processes of rain splash and sheet wash.

b.  Rain splash on bare slopes may cause rills to form. These sometimes turn into gullies and badlands.

c.  Rain splash on slopes of unconsolidated material may produce earth pillars.

E.   Rivers and river basins

1.  The water cycle

a.  It is the transfer or movement of water in its three different states (solid, liquid and vapour) between the atmosphere.

b.  The transfer or movement of water in the water cycle involves:

→ The addition of water to oceans and lakes.

→ Surface run-off (rivers) plus ground water flow.

→ Evaporation (from oceans and lakes) plus evapotranspiration (from the land).

→ Water vapour

→ Condensation.

→ Precipitation and so on.

c.  Key processes of the water cycle include precipitation, evaporation, evapotranspiration, condensation, run-off and infiltration.

d.  All processes are accompanied by energy transfer.

e.  The water cycle is a closed system.

2.  River basin system

a.  Its boundary is called a watershed.

b.  A river basin is drained by a single river system which produces distinctive landforms in the basin through the processes of erosion and deposition.

c.  A river system affects the landscape of its basin. The system itself is also affected by the vegetation and human activities in its basin and by sea / land level changes.

d.  Inputs to the system are water, energy, minerals, sediments (from weathering and mass wasting), the slope of the land and vegetation. Processes of the system are evaporation, erosion, evapotranspiration, deposition and infiltration. The outputs from the system are water, sediments, minerals and organic matter.

e.  The streams of a river basin form a river network. The streams of the network are classified in a stream order. Single streams of the headwaters are called first order streams.

f.    Drainage pattern: the pattern of a river system is determined by rock structure and the surface slopes of its basin. Five common drainage patterns are dendritic, radial, rectangular, trellis and centripetal.

3.  The flow and work of rivers

a.  The energy of a river depends on its velocity and its discharge. Frequently, a river’s energy increases as the velocity and discharge increase.

b.  A river’s energy is used to overcome friction with the wetted perimeter of its channel, to erode the sides and bed of its channel and to transport its load.

c.  River erosion consists of the processes: hydraulic action, attrition, corrasion (abrasion) and solution (corrosion).

d.  A river transports its load by traction, saltation, suspension, floatation and solution.

e.  The size of a river’s load depends on the amount of energy it has, i.e. on its velocity and discharge.

f.    Deposition occurs when a river a river’s load increases or when its gradient decreases or both (which cause its velocity and hence energy to decrease).

4.  Long profile of a river

a.  The long profile of a river shows the view along a river from its source to its mouth.

b.  It usually consists of three sections: upper, middle and lower courses. In Hong Kong, most rivers have upper and lower courses only.

c.  River processes along the profile:

Upper course - mainly vertical corrasion.

Middle course - mainly lateral corrasion but deposition increases.

Lower course - mainly deposition.

d.  When sea level falls or land level rises, a river is rejuvenated and the features formed are knickpoint and terraces.

e.  When sea level rises, the lower course of a river is ?#060;b style="mso-bidi-font-weight:normal">drowned? and a ria forms.

5.  The cross-sectional profile of a river

The cross-sectional profile of a river shows the view across a river and its valley in each of the three courses:

Upper course - the valley is narrow and steep-sided (V-shaped). The bed of the channel has a steep gradient.

Middle course - the valley is more open, valley sides are not as steep (Open V-shaped). The bed of the channel has a less steep gradient.

Lower course - the valley is wide, the floor is flat. The bed of the channel has a low gradient.

6.  Fluvial landforms

a.  Upper course: interlocking spurs, waterfalls, plunge pools, potholes, rapids.

b.  Middle course: meanders, bluffs.

c.  Lower course: flood plain, levees, meanders, cut-off, ox-bow lakes, braided river, deltas, distributaries.

F.   Coasts

1.  The coast as a zone of interaction

a.  It is a zone of interaction where the atmosphere, hydrosphere, lithosphere and biosphere meet and interact.

b.  It is an open system in which processes involving wave erosion, deposition (from waves, wind and rivers), transportation (waves and wind), energy (from solar radiation) and the actions of plants and animals (including human kind), all operate.

2.  Waves

a.  They are caused by winds and have a circular motion.

b.  Wave size is directly related to the strength and persistence of the wind.

c.  The energy of a breaking wave depends on the size and height of the wave.

d.  A breaking wave produces swash and backwash.

e.  A wave is constructive when the swash is greater than the backwash. It is destructive when the backwash is greater than the swash.

f.    Waves breaking obliquely to the coast produce longshore drift.

g.  Waves are refracted by an indented coast.

h.  The rise and fall of tides allow waves to affect a broad coastal area of several metres in vertical extent.

i.    Waves eroded, transport and deposit.

3.  Erosional landforms

Cliff and wave-cut platform

a.  Waves cut a notch in the land at high water level and gradually undercut the base of the notch. A cliff develops.

b.  Continual wave erosion plus weathering and mass wasting of the cliff face cause cliffs to retreat. A gently sloping rock surface called a wave-cut platform develops.

c.  Cliffs cease to retreat when the width of the wave-cut platform and the shallow water over this prevent waves from breaking against the cliffs.

d.  The eroded materials from the cliff transported by the backwash may be deposited in the deeper water offshore to form a wave-built terrace (depositional landform).

e.  Hong Kong examples: volcanic cliff - Rocky Harbour, granite cliff - Shek O, wave-cut platform - near Sham Chung, Ping Chau Island.

Cave, blow hole, geo, arch and stack

a.  Wave erosion can develop a tunnel-like hole in a weak area near the base of a cliff called a cave.

b.  A cave may connect via a joint with the top of the cliff. The opening here is called a blowhole.

c.  A geo forms if the roof of a cave collapses.

d.  Sometimes a cave is eroded right through a narrow headland. The cave then turns into an arch.

e.  A stack forms when the top of an arch collapses.

f.    Hong Kong examples: geo - Cheung Chau, arch - Bluff Island and Ap Chau, stack - Po Pin Island.

4.  Depositional landforms

Beach

a.  A beach forms when swash deposits sand or pebbles or boulders in shallow water along a coast.

b.  Beaches vary in type according to the size of their rock particles.

c.  Hong Kong example: sand beach - Repulse Bay, pebble beach - Tai A Chau (Soko Islands), boulder beach - Shan Shek Wan.

Spit

a.  A spit is a narrow, sometimes curved bar of sand or pebbles which projects into the sea from the land.

b.  A spit is formed by longshore drift depositing its load in calm water.

c.  Hong Kong examples: Pui O (Lantau), Silver Mine Bay.

Tombolo

a.  If a spit grows and joins an island to the mainland or joins two islands, it is called a tombolo.

b.  A tombolo is formed by longshore drift deposition.

c.  Hong Kong examples: Sharp Island, Cheung Chau.

5.  Types of coast

The interaction of (i) sea level changes, (ii) rock structure, (iii) land slope, (iv) glacial and fluvial processes result in four basic types of coast.

a.  Ria coast

It develops when sea level rises along a coast where mountain ranges and river valleys are oblique or at right angles to the coast. The lower sections of the valleys are drowned and they form rias.

b.  Concordant coast

It develops when sea level rises along a coast where mountain ranges and river valleys are parallel to the coast. The lower sections of the valleys are drowned and they form inlets.

c.  Fiord coast

It develops when sea level rises along a glaciated mountain coast drowning the lower sections of the glaciated valleys which become fiords.

d.  Emerged coast

It develops when either sea level falls or the land rises.

PART 2 - The land: Weather and climate

G.  Elements of climate: temperature

1.  Atmosphere

a.  Most of the atmosphere’s gases are in the troposphere.

b.  Short-wave energy is converted into long-wave terrestrial energy at the Earth’s surface. Terrestrial energy heats the atmosphere at the Earth’s surface and the heat is circulated through the troposphere.

c.  Weather refers to the nature of the elements of climate for a particular place at a particular time.

d.  Climate refers to the average state of the elements of weather over a long period of time.

e.  The elements of climate are temperature, pressure, humidity, wind, cloud cover and sunshine.

f.    The elements of climate result from the transformation of terrestrial energy in the troposphere.

2.  The Earth-atmosphere system

a.  It consists of the Earth and the atmosphere, i.e. the whole planet.

b.  It is a closed system.

c.  34% of solar energy reaching the atmosphere are reflected back to the space, 66% pass into the atmosphere and 20% absorbed by water droplets, water vapour and dust, and the remaining 46% reach the Earth’s surface where they are converted into terrestrial energy.

d.  Terrestrial energy warms the troposphere by radiation, conduction and convection. Terrestrial energy is the atmosphere’s main source of warmth.

e.  The process of condensation (water vapour to precipitation) releases stored solar energy as heat energy. This is a minor source of warmth for the atmosphere. Warmth also comes from adiabatic heating.

f.    Eventually the atmosphere loses its energy through long-wave radiation to space. The amount radiated equals the amount of solar energy received. This is called the global energy balance.

3.  Heat transfer

a.  Heat is transferred from the atmosphere to the Earth and back, as well as from one part of the atmosphere to another part.

b.  The transfer of heat is effected by the processes of radiation, conduction, convection, condensation and evaporation.

c.  Evaporation results in heat energy being stored in water vapour as latent heat. This is released when condensation takes place.

d.  Clouds prevent the free flow of terrestrial energy to space. They radiate some of the energy back to the Earth which in turn re-radiates it back to the clouds. In this way some of the terrestrial energy is trapped. This is called the greenhouse effect.

4.  Factors influencing temperature

a.  The main factors influencing temperature are latitude, altitude, distance from the sea, ocean currents, winds, humidity and cloud cover, aspect and length of day.

b.  Latitude - the sun’s rays pass through thicker layer of air in high latitudes and more energy is lost. Also, the greater the angle of the sun’s rays, the smaller the surface area they affect and hence the more terrestrial energy they produce.

c.  Altitude - temperature falls by 6℃ for 1000m ascent in stationary air. This is called the environmental lapse rate (ELR).

d.  Distance from the sea - water warms and cools more slowly than land and in temperate latitudes the sea is warmer than the land in winter. The warming influence of the sea decreases from the sea.

e.  Ocean currents - warm and cold currents can both influence the temperature of coastlands but warm currents have more influence because many of them lies under prevailing winds.

f.   Humidity and cloud cover - act as regulators controlling radiation to and from the Earth’s surface. This results in high diurnal range of temperature for hot deserts but a low range for equatorial regions.

g.  Aspect - south-facing slopes are warmer than north-facing slopes in the Northern Hemisphere. The reverse is true for the Southern Hemisphere.

5.  Measurement and mapping of temperature

a.  Temperature is measured by a thermometer.

b.  Maximum and minimum temperature readings are used to calculate:

i. Mean daily temperature

ii. Mean monthly temperature

iii. Mean annual temperature

iv. Daily range of temperature

v. Mean annual range of temperature

c.  Places having the same temperature after adjustment for height are joined by an isotherm on a temperature map.

6.  World spatial pattern of temperature

a.  The temperature patterns for January and July clearly show the influence of factors such as distance from the sea, ocean currents and latitude on global temperatures.

b.  Since temperatures are adjusted for height, the influence of altitude is not apparent.

H.  Elements of climate: atmospheric pressure and winds

1.  Atmospheric pressure and winds

a.  The weight of air passing down onto the Earth’s surface is called air pressure. It is measured in hectopascal (hPa).

b.  Air pressure is affected mainly by several factors: temperature, altitude and the rotation of the Earth.

c.  These factors result in the division of the atmosphere into large zones of:

i. Low pressure (Doldrums / tropical low pressure and temperate low pressure)

ii. High pressure (polar high pressure and House Latitudes / sub-tropical high pressure)

d.  Air flows when there is a difference in air pressure. It always flows from high pressure to low pressure along the pressure gradient. The steeper the gradient, the faster the air flows.

e.  The winds developed by the global pressure systems operate over large surface areas. They are regular and are called prevailing winds.

f.    The main prevailing winds are Polar Winds (Polar Easterlies), Westerly Winds (Westerlies) and Trade Winds. The latter are modified by intense pressure systems in Asia to give monsoon winds.

g.  Ferrel’s Law summarises the effects of the Earth’s rotation on objects moving over the Earth’s surface.

h.  Prevailing winds enable the global balance of pressure and temperature to be maintained in space and time.

2.  Measuring and recording pressure and winds

a.  Air pressure is measured by a barometer and is shown on a weather chart by an isoline called an isobar.

b.  Wind direction is given by a wind vane. A wind is named after the direction from which it blows.

c.  The speed of a wind is measured by an anemometer.

d.  A wind is shown on a weather chart by an arrow which shows direction. Pennants (feathers) at the end of the arrow which show wind speed.

3.  Spatial pattern of pressure for the world

a.  In the northern summer, strong low pressure systems cover the interiors of North America and Asia. The Doldrums move northwards and the high pressure of the Horse Latitudes forms separate cells over the oceans. In the Southern Hemisphere, the Horse Latitudes high pressure forms a continuous belt around the Earth. A high pressure cell covers central Australia.

b.  It the northern winter, strong high pressure systems cover the interiors of North America and Asia, linking up with the House Latitudes high pressure. The Doldrums move southwards. It the Southern Hemisphere, the high pressure of the Horse Latitudes forms separate cells over the oceans. A strong low pressure cell covers central Australia.

4.  Air masses and fronts

a.  An air masses is a very large volume of air up to 2000km wide whose temperature and humidity are fairly uniform.

b.  The four main types of air masses are Equatorial, Tropical, Polar and Arctic / Antarctic. They are subdivided into continental and maritime according to the surface over which they form.

c.  They zone where two air masses meet is called a front. This is a zone of transition.

d.  There are two main fronts: Arctic Front and Polar Front.

e.  The Inter-tropical Convergence Zone (ITCZ) lies between the converging hot air of the N.E. Trades and S.E. Trades.

5.  Monsoon systems

a.  Monsoon refers to the seasonal reversal of winds.

b.  The winds of the East and South-east Asian Monsoon System operate between the high pressure over central Asia and the low pressure over central Australia in the northern winter, and the high pressure over central Australia and the low pressure over central Asia in the northern summer.

6.  Anticyclones and depressions

a.  An anticyclone is a large body of high pressure whose circulation is clockwise in the Northern Hemisphere and anticlockwise in the Southern Hemisphere flowing out from a high pressure centre.

b.  An depression is a smaller body of low pressure whose circulation is anticlockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere flowing towards a low pressure centre.

c.  Temperate depressions develop along the polar front.

d.  A temperate depression has a cold front at its rear and a warm front at its front. When two fronts meet the depression is occluded.

7.  Local winds

a.  A wind which blows over a small surface area for a few hours only is called a local wind.

b.  Some local winds descend down mountain slopes, e.g. Chinook and Föhn. These may be caused in part by differences in air pressure between the windward and the leeward sides of the mountain, and in part by warm air being drawn down from the upper troposphere by eddy currents.

c.  Descending local wind raise the temperature.

d.  Local winds develop in coastal areas when where is a marked temperature different between the air over the sea and the air over the land. These winds are called sea and land breezes.

I.     Elements of climate: condensation and precipitation

1.  Humidity

a.  Humidity refers to the amount of water vapour in the air.

b.  When the air can hold no more water vapour at a given temperature, it is saturated.

c.  Humidity is measured by a hygrometer (wet and dry thermometers).

d.  Relative humidity is the ratio between the absolute humidity and the amount of water vapour it could hold.

2.  Condensation

a.  Condensation takes place when:

i. Air is saturated either by the addition of water or by cooling it to its dew point.

ii. The air contains hygroscopic nuclei.

b.  Dew, frost, mist, fog and cloud are forms of condensation.

c.  Advection fog often occurs in Hong Kong between March and April.

3.  Precipitation

a.  Precipitation refers to rain, snow, sleet and hail.

b.  There are three types of rain: convection, relief (orographic) and cyclonic (frontal). All are caused by uplift.

c.  Thunderstorms are caused by powerful upsurges of convection currents.

d.  Rainfall is measured by a rain gauge.

e.  Rainfall is shown on map by isohyets.

4.  Global rainfall patterns

a.  Variations in global rainfall are the result of:

i. The four global pressure systems (two high and two low).

ii. Seasonal air pressure changes over continental interiors of Asia and North America.

iii. North and south seasonal migration of the global pressure systems.

b.  The global pressure systems cause surface airflow convergence in equatorial and temperate latitudes and surface airflow divergence in the Horse Latitudes and Polar Latitudes. This results in great rainfall variations.

c.  Seasonal changes in pressure over Asia and Australia result in the reversal of prevailing winds. This is the cause of the monsoon climate.

5.  Climatic types

a.  The climate of a place is determined by five factors: (i) latitude, (ii) pressure systems, (iii) distance from the sea, (iv) altitude, and (v) ocean currents.

b.  Most climates can be cassified as follows:

i. Fairly uniform - Equatorial, Hot desert, Cool temperate maritime, Arctic.

ii. Seasonal - Monsoon, Savanna, Mediterranean, Tundra.

J.    Weather and climate of Hong Kong

1.  The weather of Hong Kong

Characteristics features

a.  Actual temperature and rainfall vary from day to day especially in the autumn, winter abd spring seasons.

b.  The amount of rainfall on any particular day varies from one part of Hong Kong to another.

c.  Day to day weather during the spring varies considerably.

d.  The difference between actual monthly and mean monthly rainfall can often be large.

2.  The climate of Hong Kong

Characteristic features

a.  Seasonal reversal of prevailing winds is mainly from the north-east in the winter and from the south to south-east in the summer.

b.  There are four seasons.

c.  Heavy rain is brought by on-shore southerly winds in the long summer. The summer is hot (mean daily maximum and minimum temperatures of 28℃ and 20℃), humid (mean relative humidity of 82%) and tropical cyclones occurs.

d.  The autumn is cooler and drier with mainly easterly winds.

e.  The winter gets colder from November to February with mean monthly temperatures falling from 21℃ to 10℃. Winds are from the north-east. Humidity falls to a mean of 69%.

f.    The spring has changeable weather caused by the mixing of cold, dry continental air and warm, moist tropical air. Low pressure troughs are common.

g.  The mean annual rainfall is about 2200mm.

h.  The mean annual temperature is about 22.5℃ with an annual temperature range of 13℃ approximately.

3.  The monsoon system

a.  Hong Kong lies in the path of monsoon winds caused by differences in temperature and air pressure over the land and the sea.

b.  Warm southerly winds bring heavy rainfall in summer. Cold northerly winds bring lower rainfall in winter.

c.  Hong Kong’s climate is also influenced by tropical cyclones in the summer and troughs of low pressure in the summer and spring.

4.  Tropical cyclone

a.  A tropical cyclone develops between 6?and 20°N and 6?and 20°S over oceans whose surface water is at about 26℃.

b.  It is an area of very low pressure.

c.  The Hong Kong Observatory recognises four types of tropical cyclone based on wind strength - (i) tropical depression, (ii) tropical storm, (iii) severe tropical storm and (iv) typhoon.

d.  A tropical cyclone is funnel-shaped: the centre of the funnel is called the eye and the part that surrounds it is the vortex.

e.  The air inside the eye is fairly clam because it is descending. The air in the vortex surges violently upwards resulting in torrential rain and thunderstorms.

K.  Interpretation of Hong Kong weather charts

1.  The weather chart

a.  Weather charts show the elements of weather recorded by many weather stations.

b.  Symbols on the weather charts of Hong Kong represent the following:

i. Atmospheric pressure.

ii. Temperature.

iii. Wind direction and wind speed.

iv. Precipitation.

v. Fronts.

c.  Addition weather information is given on the reverse side of weather charts of Hong Kong.

2.  Pressure systems seen on weather charts

Anticyclone

a.  This is an area of high pressure which occurs over China in the winter. Its air is very cold and dry and it circulates in a clockwise direction.

b.  Anticyclonic weather in Hong Kong usually means clear skies, bright sunshine, cool air with day temperatures of 14 / 18℃ and night temperatures of 10℃ or less. Dew forms at night and mist often occurs in the early morning.

Ridge of high pressure

a.  It isobars form a tongue-shaped pattern.

b.  It brings fine weather and light out-blowing winds.

Depression

a.  This is an area of low pressure which develops over China in the summer. Its air is warm and moist and it circulates in an anticlockwise direction.

b.  A depression brings variable weather to Hong Kong - rain may be in showers or as heavy downpours, plenty of cloud alternating with clear skies and sunshine, often hot and sticky.

Trough of low pressure

a.  It can be recognised on the weather chart by a thick black line. It develops in the summer.

b.  It brings variable weather - light winds or no winds, light rain or thunderstorms or no rain at all, fairly high temperatures.

Col

a.  A col develops between two high pressures which are at right angles to two low pressures.

b.  A col may bring fog in winter and thunderstorms in summer.

c.  The weather in a col is variable.

Temperate depression

a.  This differs from a tropical depression in that it develops cold and warm fronts.

b.  This type of depression occurs over Japan and over similar places where polar and tropic air meet.

Typhoon

a.  This is an atmospheric system of intense low pressure with its isobars forming a circular pattern.

b.  It develops over the western Pacific Ocean during the summer and it moves in a westward direction.

PART 3 - The land: Ecosystem

L.   Ecosystems

1.  The ecosystem

a.  This is a part of the environment in which the biotic components are interlinked and interact with the abiotic components and between which energy and matter are transferred.

b.  Biotic components refer to the living components such as plants, animals and microorganisms. Abiotic components refer to the non-living components such as water, soil, minerals and air, etc.

c.  Biomass is the total amount of living organic matter in an ecosystem. Biome is a large-scale ecosystem which is dominated by a specific type of vegetation.

d.  All ecosystems occur in the biosphere, the zone where the atmosphere, hydrosphere and lithosphere meet.

2.  Processes of the ecosystem

a.  The two major processes of an ecosystem are:

i. The energy flow.

ii. The nutrient cycle.

b.  Energy flows through an ecosystem in stages - from producers (plants) to consumers (animals) to decomposers and then to space as heat energy.

c.  The energy flow is achieved through food transfer by a process called the food chain.

d.  The energy flow begins with solar energy which drives the process of photosynthesis. Photosynthesis converts carbon dioxide and water into carbohydrates (foods) in the leaves of plants.

e.  As energy is transferred some is lost as heat energy to space. Energy eventually leaves the ecosystem and returns to space.

f.    Nutrients move from the biomass to the litter to the soil and back to the biomass. This movement is called the nutrient cycle.

g.  All nutrients are recycled and one of the most important of these is carbon which is a component in respiration and photosynthesis and a principal component of food.

h.  Matter does not leave an ecosystem, energy does.

3.  The rainforest ecosystem

Location and characteristics

a.  It is located on either side of the Equator mainly on lowlands where annual temperatures and rainfall are high with rainfall evenly distributed throughout the year.

b.  It has an enormous variety of plants and animals.

c.  It is the most complex ecosystem in the world.

d.  Its main components are:

i. Abiotic: solar energy, nutrients, water, gases such as oxygen and carbon dioxide.

ii. Biotic: green plants (producers); animals, insects and birds (consumers); fungi and microorganisms (decomposers).

e.  Plants of the rainforest form layers:

i. Emergents in the top layers.

ii. Canopy trees in the layer below.

iii. Small trees and shrubs in the next layer down.

iv. Ferns and mosses in the bottom layer.

f.    Epiphytes extend across the four layers.

4.  Human impact on the rainforest ecosystem

a.  Large areas of rainforest have been destroyed for:

i. Cultivation (shifting cultivators and peasants farmers).

ii. Ranching (wealthy landowners or businessmen).

iii. Logging and fuel.

b.  The destruction of the rainforest results in:

i. Leaching of nutrients out of soil.

ii. Soil erosion.

iii. Increase in level of carbon dioxide in the atmosphere.

c.  Main reasons for rainforest destruction:

i. Poverty of landless peoples in the tropics.

ii. Demand for tropical timber in developed countries.

iii. Land speculation (mainly in Brazil).

d.  To prevent complete destruction of the rainforest, it will be necessary to rigidly control forest destruction eventually stopping it altogether. Introducing forest management and forest ‘farming?

Continued of Part 4 in Section B's summary! / Skip to Section C