About this book - Singapore Asia Publishers Pte Ltd (SAP)

About this book
MODEL ANSWERS TO O LEVEL TOPICAL GEOGRAPHY contains the suggested answers to
the questions in the book, O Level Topical Geography.
Suggested answers are provided for:
• Topics 1-6,
• Latest Examination Papers.
Students will find this book useful as a guide when preparing for their GCE O Level Geography
Examination.
The Editorial Team
CONTENTS
THEME 1: OUR DYNAMIC PLANET (Physical Geography)
Topic 1 Coasts........................................................................................................ A1
Topic 2 Tectonics Hazards and Landforms............................................................ A9
Topic 3 Weather and Climate................................................................................. A16
THEME 2: OUR CHANGING WORLD (Human Geography)
Topic 4 Global Tourism ......................................................................................... A25
Topic 5 Food Resources......................................................................................... A32
Topic 6 Health and Diseases .................................................................................. A38
O LEVEL GEOGRAPHY EXAMINATION YEAR 2014 PAPERS 1 AND 2....... A40
Answers
1.
1 Coasts
(a) (i) The photograph shows a coastline with headlands and wave cut platforms. There is also a small bay between
the two headlands. These headlands are sea cliffs with steep slopes. On these cliffs, we can see sea caves
being formed on the slopes. As seen in the foreground of the photograph, there are wave cut platforms
before the cliffs. These wave cut platforms are formed by the constant retreating of the waves. The waves
cut into the bottom of these cliffs causing the upper part of the cliff to collapse under its weight in a process
known as mass wasting. Hence, pieces of rock fragments can be seen on the wave cut platforms. The bigger
and heavier rock fragments are found near to the cliff slopes while the smaller and lighter ones are found
nearer to the water’s edge. The difference in colour of the lower portion and the upper portion of slopes of
the headlands shows the highest level to which the water rises. Most of the wave cut platform is exposed
showing that the area is experiencing a low tide. Between the two main headlands in the picture there is a
sandy portion which is known as the bay. This area is being protected from the waves by the headlands.
(ii) A wave-cut platform is a gently-sloping, coastal land surface with a cliff behind it. It is formed when
destructive waves at an exposed coast erode the steep slopes of the coast through hydraulic action, abrasion,
attrition and solution. The waves erode especially along the lines of weakness in the rock face to form a
notch. As erosion proceeds, the notch is deeply undercut and is enlarged to form a cave. When erosion
causes the roof of the cave to lose support, it collapses and a cliff is formed.
As the steep cliff retreats landwards, a gently-sloping land stretching out towards the sea from the base
of the cliff, called the wave-cut platform, is formed. Mass wasting, a process where loosened and broken
materials move downhill due to gravity speeds up the process too.
Sequence in the formation of a wave-cut platform.
when
(b) (i) The nature of rocks can affect the rate of coastal erosion depending on its composition and structure. Less
resistant rocks that may even dissolve in the sea water such as sand and clay will erode faster. Rocks such
as limestone and granite are more resistant and will take a longer time. Structures in rocks such as lines
of weakness allow the wave to break it down more easily.
(ii) The energy of waves can be affected by factors such as the length of the fetch the wind travels over, the
wind strength and the wave volume. Waves that travel over a longer fetch will have more energy as being
exposed to wind over a longer distance, they generate more energy. The wave energy is also dependant on
the wind speed as faster winds will result in bigger and stronger waves. Waves that are bigger will have
more energy too.
(c) (i) The formation of beaches is made possible by certain favourable conditions. The beach must be in a
sheltered coast such as in a bay between two headlands. Also, the waves that approach the coastline must
be constructive waves. The beaches are formed when these low energy waves deposit materials on the
coast. These waves are usually small, low waves with a long wave length and low wave height. The wave
frequency is usually less frequent with 6-8 waves per minute hitting the shore. These waves are usually
common along gently sloping coasts where the swash is more powerful than the backwash.
Answers to O Level Topical Geography
© Singapore Asia Publishers Pte Ltd
A1
Topic 1
(ii) The beach materials may vary in size on different parts of the beach because these materials come from
different sources. Bigger materials such as pebbles, stones and rock fragments come about mainly as a
result of erosion of cliffs by wave attack or having been brought down from the cliffs by mass wasting
such as landslides and slumping. The smaller materials such as sand, alluvium and clay are deposited by
the river at the coasts, transported by adjoining coasts or being stirred up from the seabed near the shore.
The longshore drift along coasts also helps to separate the larger materials from the smaller ones. The
longshore current causes pebbles and sand to travel along the coasts. Hence, the further the materials are
from their origin, the smaller the area. Also, as a result of the waves, the bigger and coarser materials, being
heavier, are left further inland when these waves are stronger during periods of storms or strong winds.
The smaller and lighter materials, however, are deposited nearer to the water’s edge as the backwash of
the waves is able to carry them over a greater distance.
2. (a) (i) Constructive waves are small low waves with long wave lengths and low heights. They are common in
places with a gentle coastal slope. Destructive waves on the other hand, are large high waves with short
wave lengths and a greater wave height. They are common in steep coastal slopes. Constructive waves
occur at a lower frequency of 6-8 breaks per min as compared to the destructive wave’s 10-14 waves. The
constructive wave has a more powerful swash then backwash which leads to sand being deposited onto
the coast and building beaches. On the other hand, destructive waves have great erosive power which
enables them to erode the coast with their more powerful backwash.
(ii) With its more powerful swash than backwash, the constructive wave forms a beach as deposition takes
place. The backwash is weak because much energy is spent overcoming the friction with the beach. The
powerful swash merely spills over when it breaks. Hence materials are carried up and deposited on the coast
much more than they are removed. As the accumulation of the deposits take place, a beach is formed over
time. As the constructive wave energy is low, depositions from eroded headlands, offshore zone, rivers and
neighbouring coasts are not washed away but instead deposited on the coast to help form the beach.
(iii) Sand dunes form on beaches when there is a large supply of dry sand accompanied by strong prevailing
winds. They are formed when an obstruction, such as a big rock, in the path of the wind creates eddy wind
currents and slows it down. The wind-blown sand is deposited against the obstruction in the wind shadow.
The building up of sand forms a small sand dune. This small sand dune itself acts as an obstruction and
causes more wind-blown sand to accumulate in its own wind shadow.
However, as seen in the picture, these dunes can be easily eroded. The method practised here is to stop
the erosion by building a net supported by poles across the loose soil. Vegetation may then grow on the
slopes of the dunes to stabilize them and in turn cause more sand to accumulate.
(b) (i) Singapore is a small country but with a growing population. Hence there is a need for more land to be
used. Land reclamation is one method Singapore has turned to, to increase its land area. However, such
land is easily eroded by waves especially by the waves in Singapore due to the deep sea bed resulting in
destructive waves. Singapore also receives powerful destructive waves during the North-east Monsoon
season which would destroy its beaches if there is no protection. Hence, to prevent the loss of sand and
the waves from eroding the coast of the reclaimed land and other natural shores, protection of Singapore’s
coastline is important. Singapore cannot afford to lose its size as it is already small and a lot of infrastructure
has been built near the shores and on the reclaimed land.
(ii) Singapore has made use of two methods to protect its shores and reclaimed land. These methods are by
using seawalls and breakwaters. The seawalls are built in front of the coastal area using granite rock or
reinforced concrete. The seawalls act as a buffer and absorb the energy of the breaking waves so that the
part of the coast will not be eroded. Such seawalls are made along the coasts of Singapore facing the Straits
of Johor as the waves here are generally more sheltered and calmer. A special type of seawall consisting
of angular large boulders called revetments, are put in place to protect the seaward end of the East Coast
shore as well as on the Southern Islands to assist in land reclamation. Seawalls have been used for a long
time but its effectiveness is now questioned. Seawalls were promoting more erosion instead because the
reflected waves was so powerful that it hindered the formation of beaches along the coast. Furthermore
seawalls need constant maintenance as they are under constant attack from the waves. Over time, they
may weaken and collapse.
As a form of coastal protection, breakwaters are more widely used in Singapore because they are more
effective. Breakwaters are built off the coast but parallel to it. They create a zone of shallow water so that
waves would break against them before reaching the coast. Due to the reduced energy of waves, sediments
are deposited on the beach-facing side of the breakwaters. Overtime, tombolos may form joining the
breakwaters to the beach.
Answers to O Level Topical Geography
© Singapore Asia Publishers Pte Ltd
A
Topic 1
Breakwaters are mainly found on the East Coast shores to protect the beaches here which are actually
reclaimed land. This method of using breakwaters is highly effective and also enables the formation of
sandy beaches. It has shown to be effective in the example of protecting the Pasir Panjang shore which
then allows lighter operations to be done on the Pasir Panjang Wharf Complex. It is also crucial to protect
the shore during the Monsoon season where it receives squalls and powerful destructive waves up to
1.2 m high. Another successful example would be the making of 4 islets acting as breakwater to protect
the already eroding man-made Siloso Beach.
3. (a) Mangrove forests are found mainly in areas experiencing the tropical climate, especially along sheltered coastal
regions and places where rivers constantly deposit clay and silt. These areas are usually in the inter-tidal zones
with salty or brackish water. These inter-tidal zones must also be sheltered from strong currents. The soil there
is muddy, water-logged and deficient in oxygen.
(b) There are several ways in which the plants in the mangrove forest adapt to the natural environment in which
they live. Mangrove forest is dense and luxuriant due to high temperatures and rainfall. They also form a dense,
continuous canopy as they compete for sunlight. Hence, little sunlight passes through the canopy to the ground.
Thus, the undergrowth is sparse.
As there are no seasonal changes in temperature and rainfall, the mangrove forest is evergreen. Due to high
rainfall, the leaves are broad and have drip tips to allow water to flow off the leaves quickly so as not to put a
strain on the plants. With high temperatures, the surfaces of the leaves are thick and leathery to reduce water
loss through transpiration.
The fruits of the mangrove trees, namely, Avicennia, are buoyant. When they drop into water, the waves and
currents carry them away to a new coastal location where they will grow. The Rhisophora, on the other hand,
has fruits which begin to grow while still attached to the parent tree and drop directly into the ground and take
root. The fruits of this species have an elongated structure with sharp tips that help the fruits anchor themselves
to the soft muddy soil.
The roots of the mangrove trees, such as the Avicennia and Sonneratia, are specially adapted to the oxygendeprived soil. At low tide, the aerial roots of the trees are exposed, allowing them to take in oxygen. Other
trees like the Rhizophera have prop roots which anchor the trees firmly in the muddy soil, while the Brugioera
trees have kneed roots that provide firm support for the soft soil.
(c) It is important that a mangrove ecosystem is conserved. It plays not only an important role in protecting the
surrounding area but it is also beneficial to people and a habitat for many organisms.
People living along coasts use the branches, trunks and barks of the mangrove trees to build houses and to make
their boats and equipment. Without these trees, they would have to look further inland for other sources of wood
supply. The presence of the mangrove ecosystem is vital for the other living things in the environment. Some
fish depend on the leaves and branches of the trees for food. These fish are in turn food for other species such
as crocodiles, birds and otters. The roots of the mangrove trees also serve as protection from the waves. Also
without the mangroves, there will be an increase in salt intrusion and siltation of coral reefs, ports and such.
The mangrove ecosystem also helps in protecting the coastal area from the winds and the sea. It helps to reduce
the force of strong onshore winds and to a certain extent, tropical winds in certain areas. The roots of the
mangrove trees are also essential in protecting the shoreline. The prop and the buttress hold the soil together
to prevent soil erosion. These roots also help in breaking the force of the waves before they hit the coast. These
roots have even shown to protect people in areas such as Thailand from tidal waves.
4. (a) (i) A destructive wave is a wave that erodes more soil from the coast than it deposits. These waves usually
have a larger backwash as compared to their swash. Destructive waves are large and high. They have
shorter wavelengths but greater wave heights resulting in them plunging when they break. They also have
a higher wave frequency and are common where there is a steep coastal slope.
(ii) Hydraulic action occurs when the force of the waves hits against the coast repeatedly causing the rocks
to weaken and become loose. These rocks eventually break off and are washed away by the waves.
Abrasion occurs when particles carried by the waves grind and hit the coast acting as pallets, thus causing
the coastal rocks to chip and break. The broken particles are then washed away.
Erosion by attrition occurs in the water when the particles being carried are thrown against one another.
The particles gradually break down into smaller and finer pieces.
Solution involves dissolving the soluble minerals in the rocks along the coast. The seawater reacts
with these minerals and removes them from their site. As a result the remaining rocks are weakened
as gaps are left behind which would then facilitate other forms of erosion such as hydraulic action to
take place.
Answers to O Level Topical Geography
© Singapore Asia Publishers Pte Ltd
A
Topic 1
(iii) Photograph A shows a cliff headland and a stack. This is formed when the waves hit the sides of the cliffs.
Such waves attack the lines of weaknesses along the length of the headland. Water surges into cracks and
fissures and traps the air in them. When the water retreats, the pressure generated causes the air to explode
which in turn remove any loosened rocks. These removed rocks further help erosion by abrasion while
the seawater itself contributes to the erosion through solution.
Over time, the cracks enlarge and form a notch, usually found at the bottom of the headland. The notch
gradually enlarges to form a cave and finally, this cave will tunnel through the whole headland to form an
arch. As the arch gets bigger and wider, the arch is not able to support the weight of the rock at the top.
The rocks eventually collapse leaving behind a stack which is separated from the headland as seen in the
photograph.
notch
crack
Formation of a crack in a cliff due
to wave action
Further erosion causes the
formation of a notch
stack
arch
The notch enlarges further to
form an arch
The arch enlarges and its roof
collapses leaving behind a stack
(b) As seen in the figure, the waves change the shape of the coastline to form coastal features called headlands and
bays. This is due to the alternating bands of resistant and less resistant rocks. When the waves hit the coast, the
less resistant rocks are more easily eroded as compared to the resistant rocks. This causes the shoreline of the
resistant rocks to recede further inland. Over time, this difference in the shoreline between the different rocks
becomes more pronounced. The retreating shore land is known as the bays while the more resistant protruding
rocks are known as the headlands.
(c) When waves approach the coastline at an angle, it carries a load with it and deposits the load in the same direction
through the swash. However, the backwash of the wave moves in a direction perpendicular to the coastline.
The backwash carries down with it particles in this direction. The next incoming wave then brings the eroded
particles back to shore in the original diagonal direction. This process repeats itself causing the particles to
move in a zigzag manner in a direction lateral to the shore as seen in the diagram below. This process is known
as the longshore drift movement.
Land
Shoreline
Sediment movement
Direction of
longshore drift
Swash
Backwash
Sea
Direction of pevailing wind
The process of the longshore drift can be halted by installing man-made structures called groynes. These
groynes are built protruding out of the shore into the sea making a right angle to the coast line. They are built
at distances from one another along the entire coastline. The function of the groyne is to act as a blockage to
the lateral movement of the particles. The particles accumulate at the side of the groyne facing the longshore
drift. Hence, it is used to minimize the change in shape of the coastline due to the longshore drift.
Answers to O Level Topical Geography
© Singapore Asia Publishers Pte Ltd
A
Topic 1