Chapter 1: Living with Tectonic Hazards

Part 1: Hazards of the world

Copy when you see the star

What is a Natural Hazard

• Earthquakes

•Volcano eruption

• Tsunami

Earthquake

• Is it possible for Singapore to experience an earthquake?

• 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.– Home

– 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 handout.

• Good luck!

What is the structure of the Earth?

•Core

•Mantle

•Crust Read up on Pg 7 in your textbook

Tectonic Plate

• The crust of the earth.

• Two general types

–Continental plate

• Less Dense, heavier

–Oceanic plate

• Denser, lighter

Continental Drift

• Theory that crustal plates are constantly moving

• 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.

Continental Drift Diagram

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 change.

Continental Drift Diagram

SRP Work

• Watch the following video on Colliding Continents

• Answer the questions in the SRP handout / complete the groupwork

• http://www.youtube.com/watch?v=KCSJNBMOjJs

• 50 mins National Geographic video

Types of plate boundaries

• Convergent plate boundary

• Divergent plate boundary

• Transform plate boundary

• Refer to pg 9 textbook

Divergent platesOceanic – 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

Exercise Time

• What do you think is needed to answer this question?

– “ 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.

Part 2: Convergent plates

Plate movements

• If there are plate boundaries that are diverging, at the end of that plate, there will be convergence.

• 3 common types of convergent boundaries

–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 one another.

• 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.

Oceanic Crusts

• Beneath deep oceans

• Between 5km and 8km

• Consists of basalt

• Very dense and heavy

• Made of young rock (200 million years ago)

Continental Crust

• 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 plate

• Area where it subducts is called the subduction zone

• 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 boundaries

Oceanic-oceanic plate boundaries

Oceanic-Continental plate convergence

• When an oceanic plate converges with a continental plate.

• The dense oceanic plate is forced down into the mantle.

• A deep sea trench is often formed at the subduction zone. (Japanese deep sea trench)

• The continental plate folds and forms fold mountains and volcanoes

• The Japanese Islands were a result of such convergence.

Oceanic-Continental plate convergence

Continental-Continental plate convergence

• When two equally dense continental plates converge.

• 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 folding.

• At such plate boundaries, large mountain ranges tend to form. (Himalaya)

Continental –continental plate convergence

Transform boundary

• Occurs when plates slide past one another horizontally.

• Huge energy released when friction is overcome

• Large massive earthquakes experienced

• San Andreas Fault (California)

Exercise time

• Take a look at the handout (exercise 2).

• Using the information you have learnt so far, answer the question to the best of your abilities.

• Good luck

Review Comparison Table

Plate boundary type Associated landforms Example

Divergent Oceanic-Oceanic

Deep sea ridge

Mid-Atlantic Ridge

Divergent Continental-Continental

Rift Valley

Great African Rift Valley

Convergent Oceanic-Oceanic

Deep Sea Trench, Volcanoes, Volcanic Islands

Mariana Trench, Mariana Islands, Pacific plate and the Philippine plate

Convergent Oceanic-Continental

Deep Sea Trench, subduction zone, Volcanoes, Fold mountains

Sunda Trench, Barisan mountains, Australian plate and the Eurasian plate

Convergent Continental-Continental

Deep sea trench, subduction zone, fold mountains

Himalayas, Eurasian plate and the Indian plate

Part 3

Landforms commonly associated at tectonic boundaries

Fold Mountains

Fold Mountains

• 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.

Fold Mountains

• The major ranges are along convergent plate boundaries

• The rocky mountains

• Himalayas

• Swiss Alps

• Pg 22

Rift Valleys / Grabens

Rift Valleys

• Near divergent plate boundaries, plates pull apart, causing land displacement.

• The downward displacement forms rift valleys.

• Found commonly along divergent boundaries

• Also called Graben

• East African Rift Valley

Rift Valley diagram

Block Mountains / Horst

Yosemite National Park

Block Mountains

• When sections of the crust are pulled apart by tensional force, some parts are ripped off.

• The downward displaced areas are the rift valleys

• The blocks left behind form block mountains with steep sides.

• Also called Horst

Block Mountain diagram

Volcanoes

Volcanoes

• Landform formed by magma ejected from the mantle.

• Magma builds up in the earth’s crust to form a magma chamber.

• 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 chamber

• 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 eruption

Viscosity• 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 volcano’s shape

2 Key types of Volcanoes

1.Shield Volcanoes

2.Composite Volcanoes (Stratovolcanoes)

Shield Volcanoes

Shield Volcanoes

• Gentle sloping sides and a broad summit

• Low-silica lava (low viscosity) present

• Lava flow is fast, spreading out quickly

• Subsequent layering leads to wide base with low overall height.

• Mount Washington in America

Stratovolcanoes

Stratovolcano

• Developed from successive eruptions.

• Ash and lava (coarse fragment) accumulate over time.

• Layers of ash are locked in by subsequent layers of lava.

• 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

Mt Pinatubo

Distribution of volcanoes

• Pacific Ring of Fire is the most active volcanic activity occurs

• Many earthquakes and volcanic eruptions occur along the ring of fire

• Ring is along several converging plates (Pacific, Nazca, Philippines, Australian and Eurasian plates)

• Volcanoes can also form where plates diverge.

• Pg 29

Pacific Ring of Fire

Volcanic Eruptions

• Volcanoes fall into 3 states

–Active

–Dormant

–Extinct

Active Volcano

• Constant volcanic activity

• Currently undergoing eruption or are expected to erupt in the future.

• Mt Pinatubo, Philippines; Mt St Helens, America.

Dormant Volcano

• Currently inactive but may erupt in the near future

• Prolonged period of no volcanic activity

• Inner magma chamber still hot and active

• Mt Fuji, Japan

Extinct Volcano

• Volcanoes without current seismic activity

• 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 materials

2.Landslides

3.Pollution

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/hrcan be achieved, making it impossible to escape.

The loss people of Pompei

Landslides

• Collapse of a volcanic cone during eruption.

• Downward displacement of previous slide of volcano.

• Causes large scale damage to infrastructure and loss of life.

• Settlements near the volcano may get wiped out totally.

Landslide

Pollution

• 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.

Pollution

Effects on weather

• Sulphur dioxide reacts with water vapour in the atmosphere.

• The particles reflect the sun’s energy back into space.

• This leads to a cooling of surface temperatures on earth.

• Fall in global temperature might affect plant and animal life.

Let’s attempt an exercise on what we have covered.

• 15 - 20 minutes,

• Complete all the questions in Foolscap / space provided

• Good luck

Earthquakes

• Caused by sudden release of stored energy due to movements of crustal plates.

• 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 by earthquakes.

• 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 earth.

• Aftershocks

– subsequent smaller earthquakes that follow after a major earthquake.

–Could continue to occur months after the initial earthquake.

– 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

Population density

– 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

Earthquake Preparedness

Distance from the epicentre

• Seismic energy weakens as the distance increases from the epicentre.

• Locations further away from the epicentre suffer less from the earthquake.

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 earthquake.

• Impact on the buildings on the surface is greater. Damage is often worse.

• Liquefaction – loose soil flowing like water.

• Danger of landslides after earthquakes cause more harm.

Earthquake zones

• Tendency for earthquakes to occur along crustal plate margins.

• Tendency for earthquakes to be caused when subduction along destructive plates or slipping of transform plates

Earthquake Zones

Hazards of living in earthquake zones

• Tsunamis

• Disruption of services

• Fire

• Landslides

• Loss of lives

• Loss of property

Tsunamis

• 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

Tsunamis

• As the displaced water moves, it gathers strength and size.

• When it hits the coast, large destruction is resulted.

Disruption of services

• Loss of electricity, gas and water leads to loss of essential services.

• Broken pipelines also raise the risk of explosions.

• Roads and railway destruction make it harder to send aid.

Fire

• 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.

Landslides

• Shaking of earthquakes loosen soil.

• Along slopes and hills, original vegetation may no longer be able to hold soil.

• Landslides and mudflows cause large damage.

• 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.

Part 4

Benefits of living near a Volcano

4 key benefits of living near volcanoes

• Fertile soil

• Precious stones and minerals, building materials

• Tourism

• Geothermal energy

Fertile Soil

• Lava and ash breakdown to form fertile volcanic soils

• 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 and minerals.

• 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 fertilisers.

http://www.youtube.com/watch?v=0hCl_RXqoZk

Tourism

• Volcanic areas have dramatic landscapes.

• Scenery attracts tourists for hiking and camping.

• Volcanic areas are rich in history and attract visitors too.

• The ruins of Pompeii, Italy. The black beaches in Bali

Geothermal Energy

• When groundwater comes in contact with the hot rocks underground, it heats up and escapes as steam.

• This can be harnessed to produce Geothermal Energy.

• Large turbines are used to complete this process.

• Iceland uses Geothermal energy to power over 70% of their homes.

http://www.youtube.com/watch?v=rfUQy86ZMpQ

Why do people live in such places?

• Favorable living conditions

–Fertile soil conditions for agriculture.

• No alternative location to live in.

–Case of no choice

Review Question

• Turn to pg 47 of your textbook.

• Using that map, let’s answer the questions in the handout.