1.1 How and why do the Earth’s tectonic plates …1 1.1 How and why do the Earth’s tectonic plates move? a The Earth’s interior hasa layered structure, with different composition

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1.1 How and why do the Earth’s tectonic plates move?

a The Earth’s interior hasa layered structure, with different composition

and physical properties; the Earth’s core generates heat and convection

currents drive plate motion.

Interpret a cross-section of the Earth, with details (temperature, density,

composition, physical state) of layered structure (including the

asthenosphere); using rock samples to contrast continental and oceanic

crust.

Layers of the earth

Lithosphere- the top bit of the mantle which is solid and the Earth’s crust.

Asthenosphere- The asthenosphere is a part of the Earth's mantle, lying just

below the crust and the lithosphere. The asthenosphere is made up of rock

which is soft due to the heat of the mantle.

Inner Core- The inner core is the centre of the earth and is the hottest part of

the earth. It is a solid mass of iron and nickel. The temperature of the core is

around 5500°C

Outer Core- The outer core is the layer around the inner core. It is also made

up of iron and nickel though it is in liquid form.

Mantle- This layer is made up of semi molten rock, known as magma.

Crust- This layer is between 0-60km thick. It is made of plates of rock that

float on top of the mantle.

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Rocks

The continental crust is thicker and lighter than

the heavier, thinner oceanic crust.

Continental crust is made of rocks such as

granite. This is less dense than the oceanic

crust.

Oceanic crust is made of rocks such as basalt. This is

more dense than the continental crust.

Examine the core’s internal heat source (through radioactive decay) and how

this generates convection, which drives plate motion and generates the

Earth’s magnetic field.

Why do plates move?

The earth's tectonic

plates are in constantly

moving like giant

'rafts' on top of the

semi-molten mantle

below. However this

movement is slow and

rates vary from less

than 2.5cm /yr to over

15cm/yr.

The movement of the

earth's crustal plates

is believed to be due to

convection currents

which occur in the

semi-molten mantle. These convection currents are created by heat from within

the earth - much of which is generated by radioactive decay in the core.

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b There are

conservative,

constructive and

destructive plate

boundaries, each with

characteristic volcanic

and earthquake

hazards.

Explain the distribution

of the three plate

boundary types and

identify major plates.

There are 4 different

Plate Boundaries:

• Constructive

(When 2 plates

move apart.)

• Destructive (When

an oceanic plate

and continental

plate move

towards each

other.)

• Conservative

(When 2 plates

move alongside

each other.)

• Collision (When 2

continental plates

collide.)

• Constructive

(When 2 plates

move apart.)

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Constructive Plate Boundaries

A volcano happens on a

constructive plate boundary

because two plates are moving

apart, leaving a gap in the crust.

The pressurised magma in the

crust immediately rises through

the gap and erupts as lava as it

leaves the mantle and travels

through the crust. This builds new

land between the plates, and

builds up to form a volcano shape

(shield volcano, short and fat). As

the crust moves apart over time

more lava erupts from the mantle

to fill the gap between the plates. The eruption of lava can also build up to form

volcanic islands.

The slow movement of the plates occasionally can be felt as earthquakes as the

ground moves as the convection currents in the mantle pull the plates apart in

opposite directions.

Destructive plate boundaries

Volcanoes form on a destructive

plate boundary when an oceanic

plate and a continental plate are

being pulled towards each other by

the convection currents, the

oceanic plate is much denser and is

therefore forced to sink

underneath the continental plate

(subduction). The oceanic plate is

melted by the heat in the mantle

and the friction of grinding

against the continental plate.

The melted oceanic plate releases

carbon dioxide into the mantle,

and is therefore pressurised. This

magma finds a weak point in the

crust and forces its way out, erupting as lava and making a volcano.

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Destructive plate boundaries continued

Earthquakes happen on destructive plate boundaries because the oceanic plate

and continental plate are being dragged towards each other by convection

currents, the denser oceanic plate forces underneath the continental plate and

the plates grind together as the oceanic plate subducts into the mantle. The

movement of the grinding and friction between the plates is felt on land as an

earthquake. The oceanic plate can also become stuck against the continental

plate until some of the crust breaks, making the oceanic plate descend suddenly

into the mantle. This causes higher magnitude earthquakes.

Conservative Plate Boundaries

(When 2 plates move alongside

each other.)

Earthquakes happen on

conservative plate boundaries

because the continental plates

are being dragged past each

other, or in the same direction,

by convection currents. They are

not moving at the same speed

which causes the friction felt as

earth quakes. The plates grind

together as they pass each other

causing minor earthquakes. The

movement of the grinding and

friction between the plates is felt on land as an earthquake. The plates

can also become stuck against each other until some of the crust breaks,

as they are not moving at the same speed, when this happens the plates

suddenly move past each other, this violent movement is felt on the

plates as a higher magnitude earth quake.

Collision Plate Boundaries

Two continental plates “collide” (crash into each other)

as they are travelling towards each other. The plates

are equally dense, and therefore neither plate can sink.

They therefore “fold up” to form Fold Mountains such as

the Himalayas, like cars crumple in a crash. The impact

of the collision can cause minor earthquakes which travel

outwards in waves. THIS BOUNDARY IS NOT

ASSESSED IN YOUR EXAM.

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Examine the causes of contrasting volcanic (volcano type, magma type and

explosivity) and earthquake hazards, including tsunami (shallow versus deep,

magnitude) at contrasting example locations, e.g. Iceland and Indonesia.

Measuring volcanoes and earthquakes

Volcanic Explosivity Index

The Volcanic Explosivity Index (VEI)

shows the size or magnitude of

explosive eruptions. It is 0-8 in terms

of explosivity. Each number is equal to

ten times the one below it. It accounts

for ash fall, pyroclastic flows and other

substances ejected the height of the

eruption and duration.

Richter Scale

There are two ways to measure earthquake intensity; the Mercali scale and the

Richter Scale. The Richter Scale is outlined below.

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Mercali Scale

The Mercalli Scale has an intensity score (1-12) with a descriptive word, e.g.

instrumental. The magnitude on the Richter scale and a description of each

category is below.

Mercalli Scale

Intensity Description Magnitu

de Witness Observations

1 Instrumental 1 to 2 Detected only by seismographs.

2 Feeble 2 to 3 Noticed only by sensitive people.

3 Slight 3 to 4 Resembling vibrations caused by heavy traffic.

4 Moderate 4 Felt by people walking; rocking of free standing objects.

5 Rather Strong 4 to 5 Sleepers awakened and bells ring.

6 Strong 5 to 6 Trees sway, some damage from overturning and falling

object.

7 Very Strong 6 General alarm, cracking of walls.

8 Destructive 6 to 7 Chimneys fall and there is some damage to buildings.

9 Ruinous 7 Ground begins to crack, houses begin to collapse and pipes

break.

10 Disastrous 7 to 8 Ground badly cracked and many buildings are destroyed.

There are some landslides.

11 Very

Disastrous 8

Few buildings remain standing; bridges and railways

destroyed; water, gas, electricity and telephones out of

action.

12 Catastrophic 8 or

greater

Total destruction; objects are thrown into the air, much

heaving, shaking and distortion of the ground.

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More explosive volcanoes usually cause more damage.

The focus is the point underground where earthquakes originate, the epicenter it the

point above this on earth’s surface.

Shallow focus earthquakes (where the focus is much nearer the epicenter and therefore

closer to earth’s surface) cause more destruction than deep earthquakes, as they

produce more shaking on the surface as the waves do not have to travel as far.

DEEP FOCUS earthquakes or "intra plate" earthquakes, occur within the sub-ducting

oceanic plates as they move beneath the continental plates. Appearing along fault lines,

these are earthquakes with focus much deeper within the earth.

SHALLOW FOCUS earthquakes are commonly occurring "crustal" earthquakes, caused

by faults and movements of the continental plates. These are earthquakes with their

focus nearer the surface of the earth.

Montserrat Volcanic Eruption

Causes- Atlantic plate subducting under the Caribbean plate- destructive plate

boundary.

Volcano Type-Composite volcano (layers of ash and lava, steep sides)

Magma Type- Rhyolitic (basalt melted with silica from the earth, this is very

explosive).

Explosivity- 4 on VEI- large or very explosive.

Laki (Iceland) Volcanic Eruption

Causes- Constructive plate boundary- two plates move apart. The largest lava

flow in recorded history was generated by a fissure eruption in south central

Iceland in 1783. Known as the Laki flow, it erupted from a 25-kilometer-long

fissure to produce 12 cubic kilometers of lava, filling two deep river valleys and

covering an area greater than 500 square kilometers.

Volcano Type- Shield (chocolate button shaped- gentle sloped sides and wide

base).

Magma Type- basaltic lava (fast flowing, spreads quickly)

Explosivity- 6 on the VEI= colossal/very large.

Kashmir Earthquake

Causes- Collision plate boundary between Indian and Eurasian plates.

Shallow focus-16.2 miles under the earth. This is very unusual. This is very deep

for a crustal earthquake.

Magnitude 7.6 on Richter scale.

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Loma Preita Earthquake, California

Causes- Conservative plate boundary; North America Plate (moving South) and

Pacific Plate (moving North).

Shallow focus- 11 miles under the earth. This is very deep for a crustal

earthquake.

Magnitude 7.1 on Richter scale.

Asian Tsunami 26th December 2004

Causes- (Earthquake on destructive plate boundary) The Asian tsunami of 2004

was caused by tectonic activity beneath the Indian Ocean. A fault twenty miles

below the ocean surface ruptured, forcing one of the plates to be thrust

upwards by as much as 40 feet. The ocean above was forced upwards and the

displaced water moved out as a series of giant ripples. From the land, the first

sign of a tsunami is the water being dragged out to sea. The vertical wall of the

tsunami destroyed everything in its path

Shallow/Deep- Shallow focus- 20 miles deep.

Magnitude- 9.3 on Richter Scale.

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1.2 What are the effects and management issues resulting from tectonic

hazards?

a Volcanic and earthquake hazards affect people in different ways and at

contrasting locations.

Investigate the primary and secondary impacts of earthquakes in two named

locations, e.g. the 2005 Kashmir versus 1989 Loma Prieta earthquakes. To

include reasons for contrasting impacts on property and people.

Kashmir, Pakistan, 2005 (Developing Country)

On 8 October 2005, an earthquake measuring 7.6 on the Richter scale hit the

Kashmir region of Pakistan. The earthquake was the result of collision between

the Indian and Eurasian plates.

Effects:

Primary effects Secondary effects

Buildings collapsed.

79,000 people were killed.

Landslides, and large cracks

appeared in the ground.

Broken sewerage pipes contaminated water

supplies and spread disease.

People died of cold during the harsh winter.

Long term homelessness.

Responses:

Short term

Help took 24 hours to arrive from abroad- locals

surface searched themselves up to this time.

Long term

People were prosecuted for poor building

construction.

The army and emergency services arrived to join

the rescue effort.

Tents were given out by charities.

Aid workers arrived from abroad to find

survivors and treat the injured.

Teams from Britain used specialist search and

rescue equipment to rescue people from

collapsed tower blocks.

Schools and hospitals were rebuilt.

Building regulations were improved to

reduce damage and the death rate in future

earthquakes.

*You need to say HOW successful (evaluate) the methods used to respond to the Kashmir Earthquake and recongnise Pakistan needed

aid, and that help took too long to arrive.

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Loma Prieta Earthquake Tuesday, October 17, 1989, San Franciso, USA

(Developed Country)

Primary Impacts Secondary Impacts

63 people died.

3757 injured

Cyprus Freeway (road on stilts)

collapsed.

Bridges collapsed.

10, 000 homes destroyed

30 fires broke out.

Homes needed rebuilding.

Cyprus freeway took 10 years to

rebuild and was made more earthquake

resistant.

Many older homes which were

destroyed were rebuilt to a higher

standard.

Transport issues- traffic.

People who were now disabled needed

benefits and homes adapting.

Reasons the effects of the Kashmir and Loma Prieta earthquakes were

different:

Loma Prieta- collapsed freeway has immediate response to rescue trapped

people, Kashmir Earthquake help took 24 hours from abroad. San

Francisco had a larger search team than Kashmir.

Building standards generally higher in San Francisco therefore less

deaths and injuries.

Kashmir 5x more powerful.

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Examine the primary and secondary economic and social impacts of one

volcanic event.

Montserrat Volcanic Eruption Primary Economic Impacts Secondary Economic Impacts

The biggest eruption in 1997 killed

many farm animals and crops, these

therefore couldn’t be sold.

People lost their farms and businesses

(and therefore had no income,

creating high unemployment).

The port was destroyed, and the

airport was unsafe to use, which

halted exports (and therefore

external income).

The loss of farm land is still impacting

Montserrat’s development as it cannot

grow as many crops and therefore has

less income and has to pay for more

imports.

Key infrastructure including the main

port, airport, businesses and schools have

had to be rebuilt in the north, this was

expensive.

Montserrat had little tax income due to

residents leaving and high unemployment;

this meant the island relied on aid money

to recover.

Primary Social Impacts Secondary Social Impacts

The biggest eruption in 1997 killed 19

people.

People were traumatised and afraid.

Schools, homes and transportation

hubs were destroyed.

5000 out of the 10 000 residents left.

Lack of educational facilities limited

opportunities.

Long term homelessness and

unemployment caused a low standard of

living.

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b Management of volcanic and earthquake hazards, at contrasting locations,

ranging from short term relief to long-term planning, preparation and

prediction.

Examine the role of prediction, warning and evacuation in relation to

volcanic and earthquake hazards. Contrasting hazard resistant design in the

developed and developing world.

Developed Developing

Prediction- Seismometers monitor plate

movements to sense earthquakes that could

cause tsunamis. EARTHQUAKES CANNNOT

BE PREDICTED but patterns of smaller

earthquakes indicate plate movement and can

come before bigger quakes.

Tilt metres and seismometers sense magma

movement and plate movements which can

cause volcanic eruptions.

Prediction- Often little investment,

Developed countries provide developing

countries with warnings.

Warning- Police and army can be used to do

door- to- door evacuation.

News- TV and radio.

Leafleting.

Automated phone calls.

Warning- Police and army can be used to do

door- to- door evacuation, but there are too

few staff.

News- radios and TV used to warn.

Leafleting- charities often use helicopters to

drop in leaflets.

Evacuation- Police and army used to

evacuate, all local governments have hazard

management plans.

Evacuation- People told to evacuate but

resources are often not there to support.

Army are used on occasion.

Hazard Resistant Design:

Retrofitting- flexible steel supports

which “sway” with the earthquakes and

reduce collapsing risk.

Dampers-shock absorbing springs or

dampers can be put under buildings to

allow them to “wobble” or sway within

their foundations.

Bracing- corner supports to stop

collapse.

“Pointing”- replacing cement in house

regularly to ensure bricks are well held

together.

Hazard Resistant Design:

Ring beams- Circular beams around

houses hold the walls together and

prevent the roof collapsing inwards

onto people.

Sloped roofs- these prevent ash build

up and roof collapse.

In Nepal straw blocks are being used to

build homes as it is cheap and will cause

less injuries when the buildings

collapse. Much safer than bricks or

concrete.