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 Volcanoes2.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.Landslides3.Pollution4.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 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 earthquakes2. 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

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 literarcy 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.