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EDEXCEL -GCSE GEOGRAPHY A- UNIT 1- Topic 3 Tectonic Landscapes
3.1a World distribution of earthquakes and volcanoes.
 To be able to describe the distribution of earthquakes and volcanic eruptions on a global scale.
Past question
Describe the distribution of active volcanoes on Figure 4b. (3)
Mark all descriptive points at one mark each. Any valid point acceptable:
• in a ring around the Pacific • on plate boundaries • odd ones not on plate boundary • clusters on
the margins of continents • none in Australia
Describe the distribution of earthquakes shown on Figure 4a. Use evidence from Figure 4a in your
answer. (4)
Max 3 without evidence which can
data, places eg west of USA, or size
of earthquake.
1 mark for evidence or data
Linear (1) Near coast (1) At the plate
boundaries (1) Clustered (1) Mainly
in western USA and Alaska (1)
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3.1b The reasons why earthquakes and volcanoes occur where they do, through an explanation of
plate tectonics and hotspots.
What is plate tectonics?
This is a theory that explains why earthquakes and volcanoes are found where they are.
- The Earth’s crust is divided into seven large and 13 smaller plates.
- Plates move a few centimetres a year.
- They float on the molten mantle.
- Convection currents in the mantle cause the plates to move. The convection currents are a result of
heat from the interior of the Earth.
- The plate boundaries are where most of the earthquakes and volcanoes occur.
Three different types of plate movement due to convection currents:
- Some plates move towards each other. This is called a convergent plate boundary.
- Some plates move away from each other. This is called a divergent plate boundary.
- Some plates move alongside each other. This is called a conservative plate boundary.
Plate boundaries separate the tectonic plates from each other.
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Understanding hotspots
Some volcanoes do not occur on plate boundaries. These volcanoes are formed over hotspots.
These are fixed points in the mantle that generate intense heat (in a mantle plume). Small, long
lasting, exceptionally hot areas of magma exist under the Earth's surface which in turn sustains longlasting volcanic activity.
At areas where the pressure is greater in the mantle, magma erupts through the crust as when the
plume reaches the crust it causes the crust to dome (and crack).
Volcanoes are created if the magma rises above the ocean surface.
As the crustal plate moves over the stationary hotspot, new volcanoes are formed. Hotspots are
associated with chains of islands. Examples are the Samoa Islands and Hawaii.
As the plate moves the volcano will progressively become dormant and extinct and the volcano will
be eroded by the sea.
Figure: As the crustal plate moves over the stationary hotspot, new volcanoes are formed.
Case study: The Hawaiian Islands, which are entirely of volcanic origin, have formed in the middle of
the Pacific Ocean more than 3,200 km from the nearest plate boundary. The Hawaiian Islands are
located over a hotspot. The magma rises through the Pacific Plate to supply the active volcanoes.
Why are volcanoes located over a hot spot progressively older and eroded?
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The Hawaiian volcanoes are progressively older and increasingly eroded the further they are from
the hotspot as they were once located above the stationary hot spot but were carried away as the
Pacific Plate drifted to the northwest. Watch this short animation which shows how old volcanoes
are eroded by wave action.
Past questions:
Explain the formation of a volcano at a hotspot. You may use a labelled diagram(s) in your answer.
(4)
Hot spot volcanoes are associated with magma rising to the surface (in a mantle plume) (1). They are
found mid-plate (intra-plate) (1). This occurs as the material is less dense (hotter) than that around it
in the mantle (1). When the plume reaches the crust it causes the crust to dome (and crack) (1),
which allows magma a route to the surface. Over time eruptions will build up on the surface and this
may lead to the formation of a volcano above sea level. As the plate moves the volcano will
progressively become dormant and extinct and the volcano will be eroded by the sea.
Study Figure 4b. It shows hotspot volcanoes.
(i) In which direction is the plate moving? West
(ii) On which type of plate do hotspot volcanoes usually occur? Oceanic
(iii) Draw a labelled diagram to show how the chain of islands will change over time. (3)
Credit changes over time to 2 marks. Max 2 if not labelled.
Could show erosion of present day cone; build-up of present day cone due to volcanic activity;
development of a new volcanic cone (to east of present).
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3.1c The characteristic features of convergent, divergent and conservative plate boundaries.
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To be able to draw cross section diagrams of each plate boundary.
•
Annotated the diagrams to explain the processes.
a- Some plates move towards each other. This is called a convergent or destructive plate
boundary.
Past questions
Explain the formation of volcanoes at convergent plate boundaries. You may use a diagram(s) in
your answer. (4)
Maximum 2 marks for description. Explanations credited at 1 mark each. Max 3 marks without a
process or full sequence.
E.g. Movement of plate towards each other leads to subduction of the denser oceanic plate. High
temperatures and friction lead to the melting of the leading edge of the plate. Less dense melt rises
through the mantle wedge, and pressurises the continental crust. Cracking of the continental crust
due to collision provides a path for rising magma. Rising magma contains gas and is highly
pressurised leading to explosive eruptions. Explanation can be achieved through reference to
subduction, melting, low density rising magma, and build-up of pressure.
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b- Ocean-to-ocean boundaries
c- Continental-to-continental boundary
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2- Divergent or constructive boundaries
Describe and explain the characteristic features of a constructive boundary. (4)
What are the features? Mid-ocean ridges, volcanic islands and earthquakes are the features of a
constructive boundary.
The question asks for an explanation , i.e. the reasons for these features. You may answer this
question using the ‘case study’, i.e. located example, of the Mid-Atlantic constructive boundary. The
use of a located example may be part of the question: With the aid of a located example, describe
and explain…
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Constructive boundary on land
3- Conservative or transform boundaries
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Past questions
Explain how volcanoes occur at divergent plate boundaries. (4)
Maximum 2 marks for description. Explanations credited at 1 mark each.
Max 3 marks without a process or full sequence. E.g. - Formation of volcanoes at DPB: Magma rises
due to convection currents, leading to pressure and doming of the crust (oceanic). Magma rises
through the weaknesses in the crust. Eventually (low viscosity) magma erupts onto the surface. The
continued movement of plates pulls the plates apart leading to more effusive eruptions.
Compare the characteristic features of convergent plate boundaries and conservative plate
boundaries. (4)
Max three without comparative statements. Max 2 if only reference to one of the required
elements. Convergent characteristic features to include fold mountains, subduction zones, trenches,
volcanoes (explosive) and earthquake activity. Conservative creates rifts or faults leading to lateral
movement of the ground and earthquakes.
E.g. At a convergent plate boundary plates subduction can lead to earthquake formation (1) due to
pressure build up between two plates (1). Earthquakes also occur at conservative plate boundaries
on fault lines (1), but due to tension (1). Subduction of the oceanic plate leads to magma formation
and explosive volcanic eruptions (1). No magma is created at conservative plate boundaries (1)
therefore there are no volcanic eruptions (1).
3.1d The measurement of earthquake magnitude (the Mercalli and Richter scales).
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Know the differences between the Mercalli (intensity) and Richter (magnitude)
scales.
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Explain how earthquakes occur with reference to the epicentre and focus of
earthquakes.
Two main methods to measure earthquakes:
The Mercalli scale
Measures the intensity of an earthquake.
 Determined by the effects the earthquke has on humans, buildings and the local
landscape.
 Classifies effects into twelve grades.
 Problem: arbitrary set of definitions based upon what people feel and their
observations of damage to buildings arouond them.
The Richter scale
Measures the magnitude of an earthquake
 Makes comparison easy
 Accurate measurents recorded by seismographs
 Logarithmic scale: each whole number represents a ten-fold increase in power.
Past question
Outline the differences between the Mercalli and the Richter scales. (3)
Mercalli measures damage (1) Richter measures strength/magnitude (1) Main difference – one is
descriptive the other is quantitative, difference in scales (1)
One mark for each definition. Difference must be explicit for full marks.
Outline ways in which earthquakes can be measured. (3)
Point mark. No credit for names of scales. 1 mark for list. Max 2 for reference to one type of
measurement.
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Mercalli – measures the damage of earthquakes (1) through observations by people (1)
Richter – measures the magnitude of the earthquake (1) through use of seismometers (1)
Focus and epicentre
Draw an annotated block diagram showing the epicentre and focus of an earthquake.
Label and annotate the diagram to explain why earthquakes occur.
Figure: Focus and epicentre
The seismic waves spread out from
the focus. The strongest waves are
found near the centre of the
earthquake. This means that the
most severe damage caused an
earthquake will happen close to
the epicenter- the point on the
Earth’s surface directly above the
focus.
Past questions
Outline a difference between the focus and epicentre of an earthquake. (2)
Focus – origin of earthquake (1) Epicentre – point on surface directly above focus
with greatest effects (1)
What is the epicentre? (1)
The point on the surface, above the focus where most damage occurs (1)
3.2a The reasons why people continue to live in areas of volcanic and earthquake activity.
Understand the economic, social and environmental reasons why people continue to live in areas
of volcanic and earthquake activity. (See handout)
Past questions
Explain the economic reasons why many people continue to live in areas that suffer from
earthquakes and volcanic activity. Use examples in your answer. (4)
Max 3 marks for 1 example. Unspecific, descriptive points max 2. Wide range of acceptable answers,
much overlapping between volcanoes and earthquakes.
Volcanic soils are especially fertile. (1) The region around Naples, Italy, is a huge wine growing area.
(1) Farmers make a good living from this. (1) Minerals such as tin, silver, gold, copper and diamonds
can be found in volcanic rocks. (1) The money that can be made by mining these precious minerals
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often outweighs the risk of volcanic activity. (1) Hazards do not happen very often. (1)
Suggest reasons why people continue to live in areas affected by volcanic eruptions. (4)
Point mark. Reasons to include:
Fertile soils (1) Extraction of minerals/metals/crystals (1) Tourism (1) Geothermal Energy (1)
Family(1) Perceived risk = low (1)
Explosive volcanic eruptions give large amounts of ash (1) this material weathers to form fertile soils
(1). The increased fertility leads to high crop yields for local farmers (1) leading to increased incomes
for local farmers (1).
Why do people continue to live in areas affected by earthquakes? (3)
Point mark. Max 2 without explanation.
Areas may be popular for tourism e.g. Turkey (1) Earthquakes could cause landslides which expose
mineral resources which can be mined (1) Areas may have and emergency plans (1) therefore
residents perceive safety (1) People feel it may not happen to them (1) Buildings are made to a
resistant level therefore perception of safety (1) Family and friends (1) Jobs / work (1)
3.2b The causes and effects of a volcano eruption* on people and the environment, in a named
location.
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Explain the causes of a named location.
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Describe the impacts on people, the economy and environment.
•
Compare the degree to which earthquake and volcanic hazards can be predicted.
•
Outline ways in which the risks can be managed.
Case study: Volcanic eruption: Montserrat, 1997
Causes of the eruption (6)
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Explain the effects.
Link effects to characteristics of the eruption
Ash deposits: The volcano produced thick sticky lava called andesite which formed a dome at the
top of the volcano until it became so heavy that it collapsed formation of a huge ash cloud. Ash
fell back on to some parts of the island depositing ash 2-3mm thick:
Add effects of ash deposits
Pyroclastic flows: Also when the dome collapsed, hot rocks, gases and ash were ejected from the
volcano causing pyroclastic flows- hot gas and rocks moving at 200kmph with temperatures around
400ºc.
Add effects of pyroclastic flows
Effects on people
1-June 1997: 19 people killed by a pyroclastic flow. Why?
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were in the Exclusion Zone.
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were too far away to hear the warning sirens - thought they would receive audible warning
from the volcano if it was going to erupt but this didn’t happen.
e.g.six of the victims were found outside houses where they had been attempting to seek
shelter.
2- Injuries such as severe burns.
3- Of the 11,000 people who lived in Montserrat, 7,000 were evacuated.
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Almost 3,000 to the island of Antigua
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Nearly 4,000 to the UK
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Some to the USA
Effects on transport
1- Cut off from air travel in 1995 when the volcano destroyed Bramble airport.
2- Port in Plymouth not destroyed by eruption so still in use
3- Emergency jetty in the north of Montserrat (where the people were evacuated)
Economic impact: The tourist industry is still suffering with few visitors.
Effects on buildings
1- Many villages were affected by ash deposits such as the villages of Fram and Trant which were
completely buried by ash flow deposits.
2- Houses were partially buried or burned by the intense heat of the pyroclastic flow.
3- Other houses in the Exclusion Zone were destroyed by direct impact of rocks.
4-Plymouth is gradually being buried by lahars (rapidly moving river of ash and water which buried
properties, vegetation and crops)
Environmental effects
Pyroclastic flows and surges:
- flattened thousand of trees.
- baked soil hard
- many rivers were blocked causing flooding
Ash and rock deposits:
- a total of 4 square kilometres of land was covered by the deposits.
- formed a thick, broad fan just north of Bethel.
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- widespread destruction in Bethel due to large rock deposits.
Past questions
Explain the effects of volcanic eruptions on the economy of a low income country. (4)
Loss of farmland (1) leading to reduced output and GDP (1), destruction of infrastructure, eg roads,
hotels, power stations (1) results in drain on resources during rebuild (1), loss of opportunities, eg
tourism, export of raw materials (1), positive impact through increase in tourist trade (1) as visitors
come to see volcanic activity (1).
Choose a volcanic eruption or an earthquake you have studied. Explain the effects of the volcanic
eruption or the earthquake on the people and the environment. (6)
Explain the effects of a volcanic eruption or an earthquake. (6)
Prediction and prevention of the effects of volcanic eruptions and earthquakes by forecasting, the
design of buildings and defences, planning and education.
To understand how the effects of both volcanic eruptions and earthquakes are reduced through
planning before the event, using a range of examples.
See handout
Past questions
It is not possible to predict earthquakes. Justify this statement. (3)
Justification can be positive or negative or a combination. Marks are only for the justification.
Negative
A variety of methods are being used by scientists to predict earthquakes but they are not completely
accurate. (1) Despite sophisticated monitoring equipment it still remains very difficult to pinpoint
exactly when an earthquake will happen. (1)
Positive
A variety of instruments can be used. A seismometer is an instrument that measures
ground vibrations caused by earthquakes. (1) Seismometers record ground movements which are
converted to radio signals. (1) These signals are transmitted to computers that record the
earthquakes 24 hours a day. (1)Tiltmetres measure tiny changes in the slope angle or "tilt" of the
ground.(1)
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Study Figure 4b (photograph) in the Resource Booklet. It shows an area of Kobe
affected by an earthquake.
(i) State the main effect shown in Figure 4b? (1)
Collapsed Highway/Bridge/Road
(ii) Explain why some buildings are still standing in Figure 4b. (3)
Some buildings are earthquake resistant (1) development of this theme – example of how uildings
are earthquake resistant (1). The Japan is a HIC therefore can afford to protect (1) Country is aware
of risks posed by earthquakes through scientific research (1) Modern buildings(1) Some explanation
required for full marks
Explain the methods used both before and after a natural disaster to limit its effects. (6)
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Explain how the effects of an earthquake can be reduced. (4)
Max 2 without explanation.
Planning and education: How locals should react in an earthquake (1), preparation of emergency
hazard kit (1), Building design e.g. flexible frames, shatterproof glass, rubberised foundations (1)
planning regulations (1)
Explain how the effects of volcanic eruptions are reduced through prediction and prevention. Use
examples in your answer. (6)