coasts, practise test 1, 2015, Answer - 2015-Sec3-Geog

Hwa Chong Institution (High School Section)
Humanities Department
Coast: Practise Test 1
Name: ____________________ ( ) Date: ________ Class : Sec 3 __
Answer all questions.
Describe the following coastal erosional processes, and explain the
conditions under which these occur:
 corrasion
corrasion is the erosion of coastal rocks by rocks carried by the
waves. These act as chiseling tools and scrape against coastal rocks,
causing erosion.
Conditions necessary would be presence of sharp, angular sand
and rocks to scrape the coastal rocks.
Also the presence of less resistant rock will hasten this process.
 Solution
This is the process where sea water reacts chemically with water
soluble minerals in coastal rocks and dissolves them.This weakens
the rocks and causes them to disintegrate.
Conditions necessary would be soluble rocks, eg limestone,
With the aid of a well labeled sketch diagram, explain how sediments
are transported along coastal areas.
Waves approach coast at an angle.
Swash carries the materials up the coast at an oblique angle,
in the same direction as the wind.
Backwash carries the materials perpendicularly down the
beach due to gravity.
This results in a zig-zag movement of materials along a coast
known as beach drift.
Geology of rocks is the most important factor affecting coastal
erosion. To what extent do you agree?
Geology of Rocks:
 Rock type, or geology plays an important role too.
 This affects the rate at which waves are able to erode the coast.
 Geology refers to the arrangement of and composition of rocks.
 When rocks are arranged in layers, eg alternate layers of hard and
soft rock, their rate of erosion is not the same.
 Soft rocks such as limestone, shale and clay will be eroded faster
than hard rocks such as granite and basalt.
 This results in headland and bays along coastal areas, eg
coastline in Phuket and South West Rocks in Australia
 But even hard rocks have lines of weakness, eg joints and cracks.
The waves attack the rock along these lines of weaknesses to
form notches and caves
 Also, rocks with mineral composition that that or chemically react
with water to form new chemicals are more prone to erosion, eg
 This is because, such rocks are gradually weakened under the
constant attack of sea water and break down.
Besides geology of rocks, there are other factors that affect
coastal erosion too.
 The bigger the waves, the more energy they have to erode the
 This is determined by wind speed and fetch
 The stronger the wind speed, the more powerful the waves, hence
resulting in greater erosion, forming erosional features like cliffs.
 When the fetch is large, the wind blows over a larger surface,
hence generating bigger waves, resulting in powerful waves.
 Such large waves have more powerful backwash than swash,
causing erosion on coasts
 However, weaker waves have a more powerful swash and result
in depositional features like spits and beaches forming at coastal
Types of ecosystems
 ecosystems in coastal areas include corals and mangroves
 corals are structures which develop on the seabed slightly
below sea level
 they are natural barriers that help to slow down the speed of
waves (absorb wave energy), hence reducing erosion of
coastal areas, eg Sungei Buloh in Singapore
mangroves have special roots that trap sediments and hence
reduce coastal erosion.
These trapped sediments can grow over time and form small
islands, thus extending the coastline seawards.
Human activities
 Coast lines are changed when land is reclaimed for building
port facilities, marinas, etc
 Coastal protection measures are built to protect vulnerable
coastal areas from erosion, eg beach nourishment in Cape
May Point in New Jersey, USA.
 Strong prevailing onshore winds such as monsoon period will
intensify coastal erosion.
 This is because wave action is much more stronger during this
 Eg along the east coast of Malaysia from Nov to March.
Tides and sea level change
 Tides affect coastal erosion, sediment transport and sediment
 During high tides, waves reach parts of the coast that may not be
subjected to wave action at low tides.
 Hence at high tides, waves erode and transport more sediments
away from the coast than at other times.
 At the end of the last ice age when temperatures rose and glaciers
melted. In some parts the rise in sea level rose up to 100m,
creating new coastlines
 Currents are large scale continuous movements of water in
seas and oceans, driven by prevailing winds
 They are important in 2 ways:
 distributing sediments
 regulating temperatures
 currents have a lot of energy and contribute to sediment
transport, deposition and coastal erosion. Hence they help to
shape coastal areas
 they also carry cool water from the north and south poles
towards the equator. Hence they create milder temperatures in
coastal areas
Conclusion: has a conclusion where he builds upon yes/no analysis of
L2 to reach a balanced conclusion, e.g. shows relative importance of
different factors, eg depends on the type of rocks in an areas,
whether the area has coastal ecosystems, etc
Support view with reference to long term vs short term
End of paper