Changing Physical Environment

AS Geography Revision - Theme 2 'Investigating Tectonic Change' WJEC Decemeber 2012

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  • Created by: Luiza
  • Created on: 24-12-12 10:35

Earth Structure

LITHOSPHERE - The crust of the earth

ATMOSPHERE - A semi-molten zone of rock underlying the lithosphere


1st Layer - Lithosphere

2nd Layer - Asthenosphere

In Between - Atmosphere


3rd Layer - Liquid

4th Layer - Solid


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Plate Patterns & Boundaries

There are 2 types of crust:

  • CONTINENTAL CRUST - this is what makes continents. It is between 25 to 100km thick but is not very dense and it is lighter than oceanic crust.
  • OCEANIC CRUST - this is located under the oceans and it made of basalt. It is between 5 to 100km thick and is so dense that it sinks into the mantle where oceanic and continental crusts meet.

The plate where 2 plates meet is called the plate boundary or margin.

Convection cells are the slow moving currents of mantle material from deep in the mantle, up to the surface, then along the surface, then eventually sinking back deep i the mantle.

They are powered by the Earth's interior heat and break the crust into pieces called plates

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Plate Boundary Processes


Constructive or divergent boundaries occur when 2 plates slide apart from each other.

They can also be know as spreading ridges or zones of sea floor spreading. 

---> <--- This is a destructive plate boundary. Also called convergent plate boundary.

A destructive plate boundary is found where a continental plate (CP) meets an oceanic plate (OP) . The OP descends under the CP because it is denser. The friction between 2 plates causes eathquakes.

The land on the edge of the continental crust gets squashed up to make fold mountains, like the Andes.

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Plate Boundary Processes 2

As the plate descends it starts to melt due to the friction caused by the movement between the plates.

Because it takes some sea water with it, it becomes less dense than the mantle around it. This means it rises.

This melted plate is now hot, liquid ricj (magma). The magma rises through the gaps in the surface, the liquid forms a volcano.

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Earthquake Hazards


  • Buildings can be damages by the shaking itself or by the ground beneath them subsiding 
  • The ground shaking may also causes landslides, mudslides and avalanches on steeper hills or mountains; all of which can damage building and hurt people


  • This is caused by ground shaking; buildings can sink into the ground due to soil liquefaction
  • Liquefaction is the mixing of sand/soil and ground water
  • Acts similar to quick sand


  • If a structure is built across a fault, the ground displacement during an earthquake could seriously damage of rip apart the structure
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Earthquake Hazards 2


  • An earthquake can break dams along the river. The water from the river or reservoir would then flood the area damaging buildings and sweeping/drowning people.


  • Caused by the by an earthquake under the ocean.
  • Can cause a huge amount of destruction.


  • Fires can be started by broken gas lines and power lines.
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Hazard Impacts

The impact of a hazard produces direct and indirect losses and disruption to the human systems including death and injury, property damage and disruption of social/communication services.

90% of hazard-related deaths occur in LEDCs while 75% of the economic losses occur in MEDCs.

SOCIAL IMPACTS - People and their quality of life. Home, family, community, health care and education

DEMOGRAPHIC IMPACTS - Impact on the population, numbers killed, injured, homeless. Migration of refugees. 

ECONOMIC IMPACTS - Insured loss, job loss, infrastructure loss, damage to industry, economic activities

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Effects of an Earthquake


- People killed or injured

- Buildings collapse, roads break up etc.

- Communications break down

- Water, gas and sewage pipes break


- Homelessness especially in LEDCs / families torn apart

- Disease if there is little fresh water and no sewage disposal

- Immense cost of re-building

- Without homes/jobs people are unable to fend for themselves (become refugees)

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Perception & Awareness of Tectonic Hazards


Risk is the exposure of people to a hazardous event. These present a potential threat to people or their possessions, including buildings and structures.

UNPREDICTABILITY - difficult to know when or where an event may occur and what magnitude size.

LACK OF ALTERNATIES - it's not easy to uproot and move to another location due to economic reasons linking to their livelihoods or lack of alternatives

CHANGING DANGERS - natural hazards vary in spcae and time so places that were once safe could now be a risk

COST VS BENEFITS - the resouces or benefits of a hazardous location may well outweigh the risks involved in staying there.

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Perception & Awareness of Tectonic Hazards 2


Earthquakes in MEDCs cause large scale economic losses but relatively little loss of life compared with similar magnitude earthquakes in developing world.

Vulnerability refers not only to the hazardous event itself, but also to the ability to recover afterwards.

EDUCATION - Level of awareness of the hazard and what protection measures can be taken

AGE -  Many disasters affect the very old or the very young to a disproportionate degree

INCOME & SOCIAL CLASS - vulnerability is not always the same as poverty

ORGANISATION - Groups of people working together either informally or at the local government level can prepare themselves better and organise relief afterwards

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Perception & Awareness of Tectonic Hazards 3


Perceptions are based on:

  • Past experiences
  • Attitudes
  • Personality & values
  • Expectations for the future


1. ACCEPTANCE: Hazards are natural events - accept the losses of the hazard

2. DOMINATION: Hazards are extreme events. They are predictable and their magnitude can be fore casted.

3. ADAPTION: Natural hazards will continue to occur. There is aneed to adjust, respond flexibly and research

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Earthquake Management

There are 3 approaches to managing the earthquake hazard:

1. MODIFY THE EVENT - Control the physical processes involved by 'technological fix' and thereby modify or prevent the hazardous event by either controlling the physical variables *not possible with earthquakes or by hazard resistant design.

2. MODIFY VULNERABILITY - Change human attitudes and behaviour towards hazards, either before or during an event. Prediction and warning *impossible to predict or community preparedness, or by land use planning.

3. MODIFY THE LOSS - The most passive response is simply to accept the losses. This is rarely an acceptable strategy. More commonly, the strategy is to share the losses by relying on Aid or Insurance.

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