Transcript of "Sec 3 Elective Geog Unit 1 Tectonics"
Chapter 1: Living with Tectonic
Part 1: Hazards of the world
Copy when you see the star
What is a Natural Hazard
• Is it possible for Singapore to experience an
• When tremors occur near fault lines, energy is
moved along the crust in waves.
• Such energy when sufficiently strong will
travel long distances.
• Over distance, the energy will reduce.
• If there is a massive earthquake in Indonesia,
we will feel it in Singapore.
What the Japanese are trained to do.
• Take a look at the next video.
• Pay attention to the specific action that the
Japanese people do in the event of an
earthquake in the following locations.
– When driving
– At the shops
• You will have to answer the worksheet after
watching the video so pay attention.
Let’s now attempt the exercise
• You have 10 minutes to
answer the questions on the
• Good luck!
What is the structure of the Earth?
•Crust Read up on Pg 7
in your textbook
• The crust of the earth.
• Two general types
• Less Dense, heavier
• Denser, lighter
• Theory that crustal plates are constantly
• Convectional currents move in the mantle due
to the variations of temperature.
• Warmer magma near the core rises, pushing
the crust above to the sides before sinking
down upon losing the temperature.
Evidence of Continental Drift Theory
• The changing shape of earth’s land
mass over earth’s history shows that
the plates are moving.
• The current location of the
continents on earth will continue to
• Watch the following video on Colliding
• Answer the questions in the SRP handout /
complete the groupwork
• 50 mins National Geographic video
Oceanic – Oceanic divergence
• Area where two oceanic plates move
away from each other
• Magma moves up to the surface and
cools to form new oceanic crust
• Mid-Atlantic Ridge
• Possible to find underwater
volcanoes at such locations.
Diagram of Divergent plate boundary
(insert water surface for oceanic)
Continental – Continental divergence
• Area where two continental plates move away
from each other
• Magma moves up to the surface and cools,
forming new land.
• Often fractures form at the plate boundary,
forming a linear depression (rift valley)
• Great African Rift Valley
• What do you think is needed to answer this
– “ With the aid of diagram (s), explain the different
types of divergent plate boundaries that you have
learnt. Give specific examples.”
– Use Foolscap paper, complete your diagrams and
short explanations with examples.
– Diagrams in pencil please.
• If there are plate boundaries that are
diverging, at the end of that plate, there
will be convergence.
• 3 common types of convergent
–Oceanic vs Oceanic plate
–Oceanic vs Continental plate
–Continental vs Continental plate
Reasons for convergence
• Plates converge due to continental drift.
• As the plates are pushed apart, they crash into
• Generally, the denser plate will subduct (sink)
below the less dense plate.
• The plate that is riding above will buckle (fold)
and massive landforms will occur.
• Beneath deep oceans
• Between 5km and 8km
• Consists of basalt
• Very dense and heavy
• Made of young rock (200 million years ago)
• Beneath the earth’s land masses
• Between 30-60 km
• Consists of lighter rock, like granite
• Wide range of rock ages, from recent to over 4
billion year old.
Oceanic-oceanic plate boundaries
• When two oceanic plates converge
• Denser plate subducts under the less dense
• Area where it subducts is called the
• A depression in the sea floor occurs at the
subduction zone and is called a deep sea
trench. (The Mariana Trench)
• Volcanic islands can also be formed at such
Oceanic-Continental plate convergence
• When an oceanic plate converges with a
• The dense oceanic plate is forced down into
• A deep sea trench is often formed at the
• The continental plate folds and forms fold
mountains and volcanoes
• Volcanoes tend to be a result if melted magma
is able to rise up through cracks in the crust
back to the surface.
Continental-Continental plate convergence
• When two equally dense continental plates
• There will still be a subduction occurring for
one of the plates. However there is a large
amount of friction built-up before it occurs.
• The strong force generated also causes
• At such plate boundaries, large mountain
ranges tend to form. (Himalaya)
• Occurs when plates slide past one
• Huge energy released when friction is
• Large massive earthquakes experienced
• San Andreas Fault (California)
• Take a look at the handout (exercise 2).
• Using the information you have learnt so far,
answer the question to the best of your
• Good luck
Review Comparison Table
Plate boundary type Associated landforms Example
Oceanic-Oceanic Deep sea ridge Mid-Atlantic Ridge
Continental-Continental Rift Valley Great African Rift Valley
Oceanic-Oceanic Deep Sea Trench, Volcanoes,
Mariana Trench, Mariana
Islands, Pacific plate and the
Oceanic-Continental Deep Sea Trench, subduction
zone, Volcanoes, Fold
Sunda Trench, Barisan
mountains, Australian plate and
the Eurasian plate
Continental-Continental Deep sea trench, subduction
zone, fold mountains
Himalayas, Eurasian plate and
the Indian plate
Landforms commonly associated at
• The rock layers on the crust are
constantly exposed to pressure
• When they are compressed, they
fold, forming fold mountains.
• To upfold is called the anticline and
downfold is called the syncline.
• The major ranges are along
convergent plate boundaries
• The rocky mountains
• Swiss Alps
• Pg 22
• Near divergent plate boundaries, plates pull
apart, causing land displacement.
• The downward displacement forms rift
• Found commonly along divergent boundaries
• Also called Graben
• East African Rift Valley
Block Mountains / Horst
Yosemite National Park
• When sections of the crust are pulled
apart by tensional force, some parts are
• The downward displaced areas are the
• The blocks left behind form block
mountains with steep sides.
• Also called Horst
• Landform formed by magma ejected from the
• Magma builds up in the earth’s crust to form a
• With repeated layering of ejected magma, the
volcano grows in height
• Found a divergent and convergent plate
boundaries where there is subduction.
• Vents are openings in the earth’s surface
with a pipe leading into the magma
• When magma is ejected onto the
surface, it is called lava. There is no
change in composition.
• Vulcanicity refers to the upward
movement of magma in the crust and
onto the surface.
Let’s take a short Brain Break
• Take a look at the
video on Mt St
Helens in America
• Half the volcano
was blown off in the
• The stickiness of the lava
• The resistance of the lava to flowing
• High viscosity flows slowly
• Low viscosity flows quickly
• Viscosity of the lava determines the
• Gentle sloping sides and a broad
• Low-silica lava (low viscosity) present
• Lava flow is fast, spreading out
• Subsequent layering leads to wide
base with low overall height.
• Mount Washington in America
• Developed from successive eruptions.
• Ash and lava (coarse fragment) accumulate over
• Layers of ash are locked in by subsequent layers of
• Tall volcanoes with concave bases formed.
• Secondary cones may develop as magma from the
vent seeps into the sides of the cone and erupts.
• Pyroclastic flow common
– Hot rock fragments and superheated gases.
• Mount Pinatubo, Philippines
Distribution of volcanoes
• Pacific Ring of Fire is the most active volcanic
• Many earthquakes and volcanic eruptions
occur along the ring of fire
• Ring is along several converging plates (Pacific,
Nazca, Philippines, Australian and Eurasian
• Volcanoes can also form where plates diverge.
• Pg 29
• Volcanoes fall into 3 states
• Constant volcanic activity
• Currently undergoing eruption or
are expected to erupt in the
• Mt Pinatubo, Philippines; Mt St
• Currently inactive but may erupt
in the near future
• Prolonged period of no volcanic
• Inner magma chamber still hot
• Mt Fuji, Japan
• Volcanoes without current seismic
• No geological evidence of eruption in
the past thousands of years.
• Almost no risk of eruption.
• Lake Toba, Indonesia
Risks of living near volcanic areas
1.Destruction by volcanic
4.Effects on weather
Destruction by volcanic materials
• Lava, rock fragments, volcanic bombs (ejected
molten lava blobs)
• Extreme temperatures of projectiles and lava
flow, destroying and killing.
• Inhaling hot gases and ash can also lead to
injury and death.
• With pyroclastic flow, speeds above 80km/hr
can be achieved, making it impossible to
• Collapse of a volcanic cone during eruption.
• Downward displacement of previous slide of
• Causes large scale damage to infrastructure
and loss of life.
• Settlements near the volcano may get wiped
• Ash particles and gases released disrupt
human activities over long distances.
• Some gases (Carbon monoxide, Sulphur
dioxide, etc) are harmful to humans
• Fine ash particles captured in the air endanger
planes and cause large monetary loss due to
grounding of flights.
Effects on weather
• Sulphur dioxide reacts with water vapour in
• The particles reflect the sun’s energy back into
• This leads to a cooling of surface temperatures
• Fall in global temperature might affect plant
and animal life.
Let’s attempt an exercise on what we
• 15 - 20 minutes,
• Complete all the questions in
Foolscap / space provided
• Good luck
• Caused by sudden release of stored
energy due to movements of crustal
• Occurs along faultlines as pressure builds
up stress and when the plates slip,
earthquakes are formed.
Key Earthquake Terms
• Seismic waves – energy that is released
• Focus – the point in the crustal plate
where the seismic energy originates.
• Epicentre – point above the Focus on
earth’s surface. Most of the energy
released travels along the surface of the
–subsequent smaller earthquakes that follow
after a major earthquake.
–Could continue to occur months after the
–Some aftershocks might be as powerful as
the original earthquake.
Depth of Focus
• The depth of focus affects the
impact felt on the surface.
• 2 key types
1. Deep-focus earthquakes
2. Shallow-focus earthquakes
Depth of focus
• Deep-focus earthquake
–70 to 700km below surface
–Smaller impact on land
–Most of seismic waves lose their
energy as they reach the surface.
Depth of focus
• Shallow-focus earthquake
–70km and above in the crust
–Greater impact on land
–Seismic waves reach surface
quickly and with more energy.
Measurement of earthquakes
• Richter scale (Pg31 in textbook)
9?? Destruction impacts thousands of kilometers of land
Factors affecting earthquake damage
• Population Density
• Level of Preparedness
• Distance from epicentre
• Time of occurance
• Soil type
– High population density affects more people
– Tendency for high-rise buildings increases damage
– Higher literacy rate in cities mean higher chance
of better preparedness.
• Higher chance of survival
• Better evacuation plans, trained rescue workers.
Level of preparedness
• Proper public training and social
awareness leads to less panic
• Repeated practice of emergency
exercise leads to familiarity of action
• Emergency preparedness kits raise
possibility of survival
Distance from the epicentre
• Seismic energy weakens as the
distance increases from the
• Locations further away from the
epicentre suffer less from the
Time of occurance
• Time of earthquake determines what
people are doing and whether they are
able to react.
• At night, people are asleep. There is less
time to react.
• In the day, survivors of an earthquake are
able to avoid subsequent accidents.
Type of soil
• Loose and unconsolidated (not packed
tightly) soil move more in times of an
• Impact on the buildings on the surface is
greater. Damage is often worse.
• Liquefaction – loose soil flowing like
• Danger of landslides after earthquakes
cause more harm.
• Tendency for earthquakes to occur
along crustal plate margins.
• Tendency for earthquakes to be
caused when subduction along
destructive plates or slipping of
Hazards of living in earthquake zones
• Disruption of services
• Loss of lives
• Loss of property
• Tsunami – an unusually large sea wave
• Formed by sudden movement of sea floor
• Possible causes
– Earthquakes at subduction zones
– Explosive underwater volcano eruption
– Underwater landslide
– Large coastal landslides
• As the displaced water moves, it gathers
strength and size.
• When it hits the coast, large destruction is
Disruption of services
• Loss of electricity, gas and water leads to
loss of essential services.
• Broken pipelines also raise the risk of
• Roads and railway destruction make it
harder to send aid.
• Earthquakes at timings where meals are
prepared raise risk of fires.
• Gas pipes and electric cables that are
broken lead to fire risk.
• Urban areas are densely populated,
hence larger fire risk.
• Shaking of earthquakes loosen soil.
• Along slopes and hills, original vegetation
may no longer be able to hold soil.
• Landslides and mudflows cause large
• Heavy rainfall after earthquakes raise the
risk of landslides.
Destruction of property and
Loss of lives
• Earthquakes destroy homes and buildings that
are not earthquake proof.
• Large amount of money needs to be spent to
rebuild the property.
• Urban areas with more infrastructure (roads,
subways) cause even more money to repair.
4 key benefits of living near volcanoes
• Fertile soil
• Precious stones and minerals, building
• Geothermal energy
• Lava and ash breakdown to form fertile
• The richest soils on earth, highly
favourable for agriculture
• Hawaii and Bali
Precious stones and building materials
• Volcanic rocks can be rich in precious stones
• After the top layers of volcanic rocks are
eroded, these can be extracted.
• The volcanic rocks at Kimberley, South Africa,
are the richest source of diamonds globally.
• Other useful materials like sulphur can be
collected from volcanic rocks. Sulphur is used
to refine sugar and make matches and
• Volcanic areas have dramatic landscapes.
• Scenery attracts tourists for hiking and
• Volcanic areas are rich in history and attract
• The ruins of Pompeii, Italy. The black beaches
• When groundwater comes in contact with the
hot rocks underground, it heats up and
escapes as steam.
• This can be harnessed to produce Geothermal
• Large turbines are used to complete this
• Iceland uses Geothermal energy to power
over 70% of their homes.
Part 5 : Responses to
‘O’ Level only
Why do people live in such places?
• Favorable living conditions
–Fertile soil conditions for
• No alternative location to live in.
–Case of no choice
• Turn to pg 47 of your textbook.
• Using that map, let’s answer the questions in
• People who accept earthquakes as
• Tend to resist evacuation in the face of an
• Common for communities in less
developed countries with limited access
to other places.
• People who live near Mt Pinatubo.
• People who accept the risk of living in
earthquake-prone areas due to the
benefits of living in that area.
• Benefit outweigh the costs of moving
• Mostly accepted by the developed
• People of Christchurch.
• People who successfully live in
earthquake-prone areas as they are well
• Use of earthquake monitoring devices,
risk assessment, technology to increase
• Costly approach but able to save many
lives and property.
• People in Taiwan and Japan.