Horizons - Sample Chapters

SYLLABUS LINK

11

1 The Tectonic Cycle ................................ 2

2 Plate Tectonics ....................................... 5

3 The Geography of Volcanoes ...........17

4 The Geography of Earthquakes .......34

5 The Rock Cycle ....................................50

6 Folding and Faulting ...........................63

7 Slope Development .............................70

8 Weathering ............................................71

9 Karst Landscape ..................................78

10 Mass Movement ................................... 86

11 Fluvial Processes, Patterns and

Landforms, and Human Interaction ...... 98

12 Coastal Processes, Patterns and

Associated Landforms, and

Human Interaction .............................121

13 Glacial Processes, Patterns

and Associated Landforms ................144

14 Isostasy ................................................162

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Chapter Chapter

2

SYLLABUS LINK

The internal structure of the Earth��

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By the end of this chapter students will have studied:

�� The internal structure of the Earth

�� The Earth’s crust

The mobility of the Earth’s crust produces endogenic forces, which give rise to geological structures within it. Crustal structures are created, modified and destroyed as part of the tectonic cycle.

1 The Tectonic Cycle

GEOTERMS

lithospherelithify

asthenosphere

asthenosphere

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Fig 1.1 The structure of the Earth

Continental crust. Composed of light rocks made from silica and alumina (SIAL). 30–70 km thick.

Ocean

Oceanic crust. Composed of heavy rocks made from silica and magnesium (SIMA). 3–10 km thick.

CRUST

Made up of solid rock Two main types, oceanic crust and continental crust

MANTLE

Made up of rock Molten or semi-molten state

OUTER CORE

Made up mainly of iron Molten/liquid state

INNER CORE

Made up mainly of iron and nickel Solid state Very high temperatures (up to 5000 oC)

NOTE !The moho. The boundary between the Earth’s crust and the mantle.

The Tectonic Cycle Chapter 1

The Earth’s crust��# �� "��$��

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Fig 1.2 The Earth’s crust

Continental crust

Continental shelf

Ocean

Oceanic crust

VolcanoOcean ridge

Rigid upper mantle

Man

tle

Light rocks – SIAL e.g. granite

Mantle consists of semi-molten rock that moves in convection currents, fuelling the movement of the plates of the Earth’s crust

Heavy rocks – SIMA e.g. basalt

Lith

osph

ere

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GEOTERMS

The moho is the boundary located between the Earth’s crust and the mantle. This boundary is located approximately 5–10 km below the ocean floor and on average 35 km beneath the continents. The moho separates oceanic crust and continental crust from underlying mantle.

i QUICK QUESTIONS

1. Name the four layers of Planet Earth.

2. Which layer do we live on?

3. Which is the hottest layer?

4. Which crust is referred to as having (a) SIMA and (b) SIAL content?

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Ordinary Level|Short QuestionsCross-section of the Earth 1. Examine the diagram on the right and match

each of the letters in the diagram with one of the descriptions below.

Outer core

Mantle, convection current

Inner core

Mid-ocean ridge

Ocean trench

A

C

E

B

D

2010, Part 1, Q1, 10 marks

Questions

3

Core Physical Environment

44

Ordinary Level|Long Questions

2. Examine the cut away diagram of the Earth. Match each of the following names with a letter from the diagram.

E

A

B

C D

2008, Part 2, Q2A, 30 marks

The marking scheme for a question like this on an Ordinary Level paper is as follows:

Total 30 marks

Higher Level|Short Questions

3. Examine the diagram of the structure of the Earth. Match each of the following terms with its correct letter in the diagram.

AB

C

D

2007, Part 1, Q1, 8 marks

Structure of the Earth:�� Crust

�� Mantle

�� Outer core

�� Inner core

�� Lithosphere: the Earth's crust and the solid upper mantle

�� Asthenosphere: partially melted layer, the lithosphere floats on top of it

The Earth’s crust:�� Continental Crust – thick,

30–70 km – light rocks – SIAL

�� Oceanic Crust – thinner continental crust, 3–10 km – heavy rocks – SIMA

The internal

structure of

the Earth

MIND M AP

5

By the end of this chapter students will have studied:�� The theory of continental drift

�� The theory of sea-floor spreading

�� Continental drift and plate movement

�� Ireland’s position now and in the past

�� Global distribution of plates

�� Plate boundaries

2 Plate Tectonics

Plate tectonics#�� ($�� # �� $��)�� $ ��"� ��$�� *��+,+-��.��$��+,�/�� # �� $�� ! �� $�� !�� $�� $� �� 0��$��& � ��'�� *�� $�� "�"��(��"��

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Convection currents

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SYLLABUS LINK

GEOTERMS

Diverging means moving in different directions from one point.

Converging means coming together from different directions to meet at a point.

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Fig 2.1 Convection currents

Plates pulling apartPlates colliding

Convection currents

Fig 2.2 Convection currents in a saucepan of boiling water

Convection currents

To best understand convection currents, observe water in a saucepan boiling.

Warning: Be careful. Do not scald yourself.

Observe the water in the saucepan as it begins to boil. Notice how air bubbles rise, then flow sideways, and then sink. This movement is of a circular motion and is similar to how convection currents fuel the movement of plates.


Core Patterns and Processes in the Physical Environment

6

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Fig 2.3 Sea-floor spreading

MID-OCEAN RIDGE

YoungestOldest Oldest

American continent

Eurasian continent

Convection currents

Convection currents

Mantle Mantle

Floor of ocean

Proof of sea-floor spreading�� 3�� "�� &�"� ��3��'�� "�� (��)�� &�� )�� "�� "�� &�� *�� $ ��$��

GEOTERMS

Glaciations refers to a period when the Earth is covered with glaciers or ice.

A mid-ocean ridge is made up of underwater mountain ranges.

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EXAM HINTS

A question on plate tectonics has appeared every year on the Higher Level paper.

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Plate Tectonics Chapter 2

7

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GEOTERMS

Subduction occurs when a heavier plate sinks and bends beneath a lighter plate.

The subduction zone is the point where an oceanic plate slides beneath either a continental plate or another oceanic plate.

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NOTE

Continental fit occurs at the continental shelves which lie below sea level and have not been eroded.

Mesosaurus lived in freshwater lakes and ponds. Mesosaurus may have seldom, if ever, ventured onto land.

Mesosauruswas significant in providing evidence for the theory of continental drift. Its remains were found in southern Africa and eastern South America.

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Fig 2.4(b) Convection currents split Pangaea into two continents

Panthalassa – an ancient ocean

Fig 2.4(a) Pangaea: The supercontinent of 200 million years ago

PA

N

GA E A

Lauras ia

G o n d w a n a l a n d


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QUICK QUESTIONS

1. Who developed the theory of continental drift?

2. Name seven major plates that make up the Earth’s crust.

3. What fuels the movement of these plates?

4. Explain briefly the process of the movement of convection currents.

5. Explain briefly the theory of sea-floor spreading.

6. What was Pangaea?

7. When did the single landmass begin to split apart?

8. What evidence, found in the rocks, is proof that the continents were once joined together?

?

Fig 2.6 Could this be the position of the continents 50 million years from now?

EuropeNorth America

Africa

South America

Antartica

Asia

Australasia

Fig 2.5 The position of our continents today

North American Plate

Antartic Plate

Indo-Australian Plate

Eurasian Plate

African Plate

South American Plate

Madagascar Plate INTERESTING FACTS

The Appalachian mountains of North America are formed by the same type of rock as the Caledonian mountains of Ireland and Scandinavia.

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Fig 2.7 The Earth’s crust is broken up into seven major plates and several minor plates

NORTH AMERICAN PLATE

PACIFIC PLATE

1

23

45

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A N T A R C T I C P L A T E

EURASIAN PLATE

AFRICAN PLATE

INDO-AUSTRALIAN PLATE

Juan de Fuca Plate1 Cocos Plate2 Caribbean Plate3 Arabian Plate4 Anatolian Plate5 Phillipine Plate6 Nazca Plate7

SOUTH AMERICAN PLATE

7

EXAM HINTS

Make sure you can recognise and label a map of the major plate margins of the world.

The Chief Examiner’s report of 2007 stated that students should familiarise themselves more with maps displaying plate margins of the world.

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Fig 2.8 Types of plate boundaries

(a) Divergent plate boundaries (boundaries of construction)

(b) Convergent plate boundaries (boundaries of destruction)

(c) Conservative plate boundaries (passive boundaries)

Magma

Plate

Plates separating

Mantle

Convection currents fuel the separating plates

Convection currents

Subducting plate melts

Convection currents

Convection currents

Plates slide past each other along the transform fault

Island arcs

NOTE

The San Andreas Fault in California, USA, is a conservative plate boundary. The plates slide past each other in the same direction along the transform fault. Because the plates are moving at different speeds it appears they are moving in different directions. See Fig 2.14 on page 12.

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Fig 2.9 A divergent (constructive) plate boundary

Younger crust

Surface of sea

Mid-ocean ridge

Older crust

EURASIAN PLATENORTH AMERICAN PLATE

Convection currents in the mantle fuel the movement

of separating plates

Oceanic crust

Crust movement

Forms as magma rises

As plates separate a rift valley forms

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Fig 2.10 A convergent (destructive) plate boundary

Subducted and melted plate rises and the subducted oceanic plate melts. It later rises and forces magma through continental crust

Sea

Deep trench

Explosive acidic lava

Volcanic mountains

Oceanic crustContinental crust

700 km

Convection currents in the mantle

Oceanic plate melts into mantle as it subducts

Mantle

EXAM HINTS

Make sure you know the different types of plate margins very well. It is important not to confuse the different types when answering an exam question.

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Fig 2.11(a) The collision of oceanic-oceanic plates

Fig 2.11(b) Japan – an example of an island arc

g ( ) p

Trench Island arc

Oceanic crust

Continental crust

Melting

Eurasian Plate

Subducting oceanic platesOceanic lithosphere

Pacif ic Plate

Japan trench

Fig 2.12 The formation of the Andes Mountains in South America

TrenchVolcanic arc

Oceanic crust

Continental crust

Melting

— 100 km

— 200 km

Subducting oceanic lithosphere

NAZCA PLATE

SOUTH AMERICAN

PLATE


12

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Fig 2.13 The formation of the Himalayas as a result of continental-continental plate collision

Ganges plainTibetan plateau

Himalayas

Subducting oceanic lithosphere

Continental crustContinental crust

AsthenosphereAncient oceanic crust

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Fig 2.14 The location of the San Andreas Fault

USAS a n A n d r e a s F a u l t

Plate movement

Fig 2.15 The San Andreas Fault

San Francisco

Los Angeles

San Diego

MEXICO

North American Plate: 1 cm per year

Pacific Plate: 6 cm per year

Buckling of continental crust

NOTE

Shallow earthquake activity may occur at convergent continent-continent plate boundaries.

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13

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QUICK QUESTIONS

1. Name three types of plate boundaries.

2. At divergent plate boundaries, what activity results in two plates moving apart? Give an example of where this occurs.

3. Explain what a rift valley is and give an example.

4. Name a volcanic island.

5. List the three types of convergent plate boundaries.

6. Name an example of an island arc.

7. What activity is associated with a conservative plate?

8. Name and locate an example of a fault line.

9. Match the margins, landforms and examples from the table.

Margin Type Landform Example

Conservative Mountain belt Andes

Convergent Volcanoes, mountains Himalayas

Convergent Fault valley San Andreas Fault

Divergent Rift valley African Rift Valley

Divergent Mid-ocean ridge Mid-Atlantic Ridge

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Fig 2.16 Ireland’s timeline

850 million years ago 350 million years ago 200 million years ago Today

Questions

14

Ordinary Level|Short QuestionsPlate tectonics 1. (a) Examine the diagram and then match

each of the named landforms in the table with one of the letters in the diagram.

Landform Letter

Volcanoes

Mid-ocean ridges

Subduction zone

Rising magma

(b) Name any volcano.

Oceanic crust

A C

B

D

Sediments

Ocean floor

Continental crust

Ocean crust moves down under continental crust

2009, Part 1, Q2, 10 marks

Plate tectonics 2. Examine the map which shows the world’s

plate margins.

(a) Name two plates which are converging (coming together).

(b) Name two plates which are diverging (pulling apart).

(c) ‘Mid-ocean ridges are formed at the edges of diverging plates (pulling apart)’. True or false?

Pacific PlateAfrican Plate



Nazca Plate Indo-Australian

Plate

Eurasian Plate

Pacific Plate

2007, Part 1, Q1, 10 marks

Ordinary Level|Long QuestionsFold mountains 3. Look at the photograph of fold mountains

in Europe. Explain with the aid of a diagram/diagrams how fold mountains are formed. In your answer name an example you have studied.

2009, Part 2, Q3B, 30 marks


Naming the example 2 marks

Diagram: two aspects @ 2 marks each 4 marks

Formation of fold mountains explained: 8 SRPs @ 3 marks each 24 marks

Total 30 marks

Plate tectonics 4. Use the diagram to explain the theory of plate

tectonics.

The lithosphere is broken up into plates. Convection currents in the mantle cause the plates to move in different directions.

MANTLE

2009, Part 2, Q3C, 40 marks


13 SRPs @ 3 marks 39 marks

Reference to diagram 1 mark

Total 40 marks

15

Plate tectonics 5. Examine the cut-away diagram of the Earth.

Match each of the following names with a letter from the diagram.

�� Continental crust

�� Outer core

�� Mantle

�� Ocean crust

�� Inner core

A

B

C

E

D


6. Examine this map of global crustal plates. With reference to the labels shown:

(a) Name the crustal plates A and B.

(b) Name the type of plate margin at C and at D.

AB

CD

SEC sample paper, Part 2, Q2A, 30 marks

Higher Level|Short QuestionsSubduction zone 7. Examine this diagram showing a subduction

zone. Pair each of the letters A to D with the correct features below.

Feature Letter

Asthenosphere

Lithosphere

Subduction zone

Volcanic intrusions

D

Sea level

Mountains

B

A0 100

kilometres

C

Folded sedimentary rock

Magma moving upwards

Magma created here

Oceanic crustContinental crust

Folded sedimentary rock

2009, Part 1, Q1, 8 marks

Higher Level|Long QuestionsPlate margins 8. Explain, with reference to examples you

have studied, how plate tectonics help us understand the forces at work along crustal plate boundaries.


The marking scheme for a question like this on a Higher Level paper is as follows:

Name two forces @ 2 marks each 4 marks

Name different boundaries @ 2 marks each 4 marks

Discussion: 11 SRPs @ 2 marks each 22 marks

Total 30 marks

Crustal plates 9. Examine the map showing the major crustal

plates of the Earth. Answer the following:

(a) Name the volcanic island at L.

(b) Which term, constructive or destructive, best describes the plate boundary at M?

(c) Name the plate at N.

(d) Which of the following statements is false?

O. As the plates move apart (very slowly) magma rises from the mantle.

P. Convection currents inside the Earth cause the Earth’s plates to move apart.

Q. The North American Plate moves eastwards.

R. Volcanoes often form at plate boundaries.

L

Pacific Plate

African Plate

Juan de Fuca Plate

Cocos Plate


Caribbean Plate


Scotia Plate

Arabian Plate


Bismarck Plate

Fiji Plate

CarolinePlate

M

N

Pacific Plate

Phillipine Plate



Four answers @ 5 marks 20 marks

Nazca Plate

1616

Sea-floor spreading 10. Examine this diagram. Answer these

questions.

(a) Name the Earth’s internal layer labelled X.

(b) Name the internal process shown by the arrows at Y.

(c) Name one mid-ocean ridge which you have studied.

(d) Name the type of plate boundary shown at Z.

Y

Sea-floor spreading

Mid-ocean ridgeOceanic crust

Lithosphere

Continental crust Continental crust

Lithosphere

Z

X


Plate boundaries 11. ‘Plate boundaries are zones where crust is

both created and destroyed.’ Examine this statement, with references to examples you have studied.


Plate tectonics 12. Answer the following questions.

(a) Name the island at A where volcanoes occur.

(b) Name the feature which can be found at B.

(c) State clearly the different types of plate boundaries found at both C and D.

African Plate

Juan de Fuca Plate

Cocos Plate



Scotia Plate

Arabian PlatePhillipine

Plate

Eurasian Plate

Caribbean Plate

Indian Plate

Eurasian Plate

Australian Plate

Australian Plate

Antarctic Plate

Nazca Plate

Equator

C

A

BD


Plate tectonics theory:�� Earth’s crust consists of plates�� Plates move, fuelled by

convection currents�� Movements results in

volcanic/earthquake activity, folding and faulting

Sea-floor spreading:�� Plates split apart, ocean floor widens, new rock is formed�� Proofs: Samples from ocean floor; new crust youngest

where magma cooled at mid-ocean, older closer to continents

�� Deposit of sediment following glaciation where continents once joined together

Continental drift theory (developed by Wegener):�� Continents transported by convection currents�� Once one supercontinent, Pangaea�

Surrounded by Panthalassa ocean�� 200 m years ago – broke apart, drifting

started – initially two sections: Laurasia and Gondwanaland

�� Subduction – continents collide, ocean between pulled down into mantle

Proofs of continental drift:�� Edges of continents fit

like jigsaw puzzle�� Matching fossils found

Sth America and Africa�� Common rocks found Sth

America and Africa�� Glacial deposits same age

Plate boundaries:�� Divergent plate boundaries – boundaries of

construction. New rock formed, mid-ocean ridges form. Plates separate and move away

�� Convergent plate boundaries – boundaries of destruction. Rock changed or destroyed as plates collide

�� 3 types: 1. Ocean-ocean 2. Ocean-continent 3. Continent-continent

�� Conservative plate boundaries – passive boundaries. Rock neither created nor destroyed. Plates slide past each other

Position of Ireland:�� 850 m years ago Adivided into two sections�� 400 m years ago A plates collided, forming Ireland.

Folding, faulting occurring�� 380 m years agoAmoved south of equator. North

Ireland above sea level, south was below�� 350 m years ago A sea level rose, covering Ireland.�� 250 m years agoA Eurasian and African Plates

collided – folding�� 200 m–140 m years agoA continental drift, Ireland

moved north�� 65 m years ago AAtlantic Ocean formed when

American and European Plates drifted apart�� Still changing today

ocean tle

MIND M AP

Plate tectonics

17

3 The Geography of Volcanoes

By the end of this chapter students will have studied:

�� Volcanic activity – how, why and where it occurs

�� How volcanoes and their effects may be predicted

�� Volcanic activity and its effects on the Irish landscape and worldwide

The development of landforms is influenced by geological structures which have resulted from the operation of the tectonic cycle.


SYLLABUS LINK

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Fig 3.1 A volcanic landscape

Pyroclastic materials

Volcanic bombs

Lava flow Spatter cone

Secondary cone in old crater

Caldera

Volcanic cone made up of layers of rock

and ash

Crater

Heated underground water results in hot springs and geysers

Magma chamber

Parasitic (secondary) cone

Vent

Cloud of ash and gases


18

Where does volcanic activity occur?=��

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Fig 3.2 The Pacific Ring of Fire and the location of the world’s major volcanoes

African Plate

Cocos Plate


South American

Plate

Caribbean Plate

Eurasian Plate

Antarctic Plate

Nazca Plate

Australian-Indian Plate

Pacific Plate

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NOTE

The pressure of the gas within the magma chamber causes the magma to rise. The magma is forced further upwards by gases expanding. When pressure from gases within the molten rock becomes too great, an eruption occurs.

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NOTE

A fissure is a long crack in the Earth’s surface through which magma erupts.

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Fig 3.3 A volcano erupting, Mount St Helens, USA

GEOTERMS

Hotspots are unusually warm areas found deep within the mantle of the Earth.

i

The Geography of Volcanoes Chapter 3

19

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GEOTERMS

The term pyroclast or pyroclastic material refers to broken-down rock. This material varies from pea- to walnut-size fragments to hardened lava blocks. It may include ash, dust, rocks and rock bombs.

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QUICK QUESTIONS

1. Explain briefly the term ‘volcano’.

2. What materials are ejected out of a volcano?

3. List three places where volcanic activity occurs.

4. Name the world’s most active volcanic and earthquake zone.

5. List three categories of volcano.

6. Explain each category of volcano and give an example of each.

7. Discuss briefly the causes of a volcanic eruption.

8. Will the presence of silica in magma lead to a violent volcanic eruption? Discuss.

9. List the materials that are ejected during a volcanic eruption.

10. What is meant by the term ‘pyroclastic material’?

?

GEOTERMS

Pyroclastic flow refers to the material that flows down the side of a volcano during an eruption. Examples may include lahars (when a snow-capped volcanic mountain erupts, the resulting mudslide is called a lahar. This happened in Nevada del Ruiz in Colombia), mudflows or nuées ardentes.

Nuées ardentes are often called glowing avalanches, as they are made up of clouds of dust, ash and gas. Many of the gases (such as sulfur dioxide and carbon dioxide) are poisonous and often more dangerous than the lava flow.

iFig 3.4 A volcanic eruption hurling volcanic bombs, ash, gases and dust into the air

INTERESTING FACTS

Pumic air-filled lava that cooled quickly can float in water. It is used by people to remove hard skin from their feet.

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Fig 3.5(a) Pahoehoe lava. This lava has a ropey texture and the flow is runny or fluid

Fig 3.5(b) Aa lava. This lava has a lumpy texture

Fig 3.5(c) Pillow lava. This appears as rounded blobs of lava. It is found on the sea floor

GEOTERMS

Constructive plate margins/boundaries are also known as divergent plate margins/boundaries.

i

NOTE

The higher the silica

content of magma, the

more viscous (sticky) it is.

Viscous magma tends to

lead to more explosive

volcanoes. Lava with a

low silica content tends to

form shield volcanoes. The

lava can flow very long

distances as it is much

more fluid.

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Location of volcanic activity=��

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Fig 3.6 The location of hotspots

African Plate

Cocos Plate


South American

Plate

Caribbean Plate

Eurasian Plate

Antarctic Plate

Nazca Plate

Pacific Plate


Pacific Plate

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GEOTERMS

Destructive plate margins/boundaries are also known as convergent plate margins/boundaries.

Hotspots are the unusually hot areas of mantle-core boundary. Examples include Hawaii, Iceland and Yellowstone National Park, USA.

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NOTE

Magma, which contains large amounts of silica, causes violent eruptions.

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Fig 3.7 A plume of rising magma at a hotspot

Volcanoes and basalt plateaus are formed from magmaLava flows out through

cracks called fissuresContinental crust is pushed up by

magma

Plume of magma rising towards the surface


22

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Intrusive structures�!�� (��$�� &��&� ��

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Fig 3.9 A batholith

Rocks in contact with and heated by molten magma change into metamorphic rocks

Rising magma moves into the

rocks of the Earth’s crustUpper mantle

Batholith

100 km

Batholith

Erosion of overlying rock exposes

batholith

Rocks not affected by batholith

Metamorphic rock

EXAM HINTS

The Leinster Batholith is also an example of an Irish volcanic landform.

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EXAM HINTS

The Leinster Batholith can be used as an example of a distinctive landscape for igneous rock (granite) in Ireland.

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GEOTERMS

The Leinster Batholith is the largest batholith in Great Britain or Ireland at 1500 km2. Over the last 400 million years it has become exposed as the top layers of rock are eroded. At 925 m above sea level Lugnaquilla is the highest peak of the Leinster Batholith.

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Fig 3.8 Intrusive and extrusive volcanic structures

Extrusives

Cool quickly

Intrusives

Cool slowly

Lava and ash

Ash cloud

Igneous intrusion

Magma chamber


23

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QUICK QUESTIONS

1. Explain the difference between acidic and basic lava.

2. Name three types of lava flow.

3. Name three places where volcanic activity may occur.

4. Explain what a hotspot is.

5. Give two examples of hotspots you have studied.

6. Explain the term ‘intrusive structure’.

7. Explain the term ‘extrusive structure’.

8. Give an example of an intrusive structure you have studied.

9. Name an intrusive rock.

10. Name a batholith located in Ireland.

11. When was this batholith exposed?

12. What category of rock usually surrounds batholiths?

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GEOTERMS

When magma squeezes in between fissures/bedding planes, it forms a sill.

When magma cuts across fissures/bedding planes, it forms a dyke.

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Fig 3.10 Intrusive features

Volcanic ash cloud

VentLava flow

Crater

Dyke

Sill

Sill

Sill

Lopolith

Laccolith

Batholith (magma chamber)

NOTE

Secondary cones form around secondary vents on larger volcanoes. Larger volcanoes can have several secondary vents in addition to the main central vent.

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24

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Fig 3.11 Volcanic cone-shaped mountain

Ash cloud

Vent

Ash

Lava flow

Lava

High-silica magma

GEOTERMS

Rock fragments produced by volcanic explosions are called pyroclasts (from the Greek pyro, ‘fire’, and clast, ‘broken’). Pyroclastic debris is also known as tephra.

i

Fig 3.12(b) Mount Kilauea, Hawaii, is an example of a shield volcano

Fig 3.13(b) Mount St Helens, USA, is an example of a dome volcano

Fig 3.14(b) Mount Vesuvius is an example of a composite volcano

Ash

Ash

Fig 3.12(a) A shield volcano Fig 3.13(a) A dome volcano Fig 3.14(a) A composite volcano

Ash


25

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EXAM HINTS

The Antrim-Derry Plateau is also an example of an Irish volcanic landform.

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GEOTERMS

The Antrim-Derry Plateau covers an area of 4000 km2 – was created 65 million years ago, and consists of 60,000 basalt columns.

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QUICK QUESTIONS

1. Explain briefly the formation of each of the following intrusive features:

(a) Sill

(b) Dyke

(c) Laccolith

(d) Lopolith

2. List four different shapes of volcanoes and give an example of each.

3. Refer to figure 3.14(c). What activity is occurring? Is this an active, dormant or extinct volcano? Explain your answer.

4. Where do fissure eruptions occur?

5. Name an Irish example of a fissure eruption.

6. How did the Giant’s Causeway form?

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Fig 3.16 The Giant’s Causeway, Co. Antrim

INTERESTING FACTS

A caldera is a cauldron-like volcanic feature. It is usually formed by the collapse of land following a volcanic eruption. Examples are found at Glencoe, Scotland and Yellowstone National Park, USA.

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Fig 3.15 A cinder volcano

Ash cloud

Cone


26

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Hydrothermal areas�� "��"�� ! ��

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Fig 3.17 A satellite image of the Hawaiian Island chain

NOTE

Hydrothermal areas are also called geothermal areas.

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NOTE

Sulfur is sometimes evident on the slopes of a volcanic cone where it is ejected through vents known as fumaroles. Sulfur is bright yellow in colour.

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Fig 3.18(a) Old Faithful, Yellowstone National Park, USA


27

The prediction of volcanic activity and its effects#��&�� &�� A�� &�� !�� &�� $�� 1�� "��

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GEOTERMS

Seismographs are instruments that measure earthquake activity. Seismographs are positioned around the sides of a volcano. When magma begins to move it creates great heat. With this heat, rocks begin to crack and break and this can lead to vibrations of the Earth’s crust. These vibrations can provide a clear indication of an imminent volcanic eruption.

i

Fig 3.18(b) A hot spring in Iceland

Fig 3.18(d) Steam and sulfur on the grand crater of the volcano on Aeolian Island, Italy

Fig 3.18(c) A black smoker on the ocean floor at the mid-ocean ridge


28

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Fig 3.19(a) Mount Etna erupting, showering ash and hot gases

Fig 3.19(c) Seismographs are used to record earthquakes under volcanoes

Fig 3.19(b) Two geologists take and record lava samples at the Volcanoes National Park on the Big Island of Hawaii for signs of future volcanic eruption

Fig 3.19(d) Scientists wear gas masks to

protect against gases emitted by a volcano

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29

Effects of volcanic activity �� $��

Positive effects of volcanic activity

Fertile soils=�� @��7��"�� "�!��$�� "��!� ��"��

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Fig 3.20 Mount Vesuvius Fig 3.21 The Pompeii forums and the Vesuvius volcano

Fig 3.22 Pompeii. The remains of original inhabitants after the volcanic eruption

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Geothermal energy+�� $�� B�� <�� "�� 1�� "��&�� G'�� !��!��&��&�� "�� "��!�� )��

QUICK QUESTIONS

1. Look at the satellite image of the Hawaiian Island chain (Fig 3.17). What do these islands signify?

2. What are hydrothermal areas?

3. List three examples of hydrothermal areas.

4. What is a geologist?

5. List six possible signs that a volcanic eruption may be imminent.

6. What are seismographs?

7. List five positive effects of volcanic activity.

8. Look at the photograph of Mount Vesuvius (Fig 3.20). Discuss briefly its role in generating tourism.

?


30

Creation of new land=�� &��!��(��$�!��

Building materials+��"�� ! ��

Negative effects of volcanic activityLaharsB�� "�� &��"�� ,�& ��"��&�� "� ��

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Nuée ardentes�� *��"�� &�� &�� $� ��$��%��

Fig 3.24 A lahar Fig 3.25 A nuée ardente

Loss of life��"��2� �� H�� 8��

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Damage to property�� !�� $��

Fig 3.23 A geyser in Iceland

31


31

CASE STUDY 3.1Effect on the environment'�� ! �� <�?�"��$��-��!�� !� �� =��G'�� B�� $��/��B�� !��B�� )��!� �� *��6��(��$�!��-�� 1��9��(�� $�� 1�� $�� 4�� +,,+�8��$��$$��

Mount St HelensOn the morning of 18 May, 1980 at 8.32 am, an earthquake measuring 5.1 on the Richter scale occurred directly below the northern slope of Mount St Helens. This triggered a landslide, the largest in recorded history. It travelled at speeds of 175 to 250 km per hour. Most of Mount St Helens’ north side turned to rubble. Thousands of trees were destroyed and the water of Spirit lake was temporarily displaced by this landslide.

The eruption of Mount St Helens could be heard 1120 km away. The magma was exposed to lower pressure and this lead to molten rock and steam exploding just a few moments after the landslide started.

The blasting of rock debris and the pyroclastic flow of extremely hot volcanic gases, ash and rocks overtook the initial landslide. Approximately 600 km2 of forest was knocked down and other parts of the forest were destroyed by the extreme heat.

The heart of the mountain had blasted upwards and gigantic clouds of ash hovered some 25 km above it. Fifty-seven people were killed. The Washington State Department of Game estimated that approximately 7000 deer, elk and bears died, as well as birds and other small mammals. Frogs, crawfish and burrowing rodents survived because they were either below ground level or under the surface of the water when the volcanic eruption occurred. The Washington Department of Fisheries estimated that 12 million salmon were killed and approximately 40,000 young salmon destroyed.

The elevation of the summit before the eruption was 2950 m. This was reduced by 401 m to its post-eruption elevation of 2549 m.

Fig 3.27 Mount St Helens

QUICK QUESTIONS

Discuss briefly how this eruption could have a negative effect on the environment.

?

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QUICK QUESTIONS

1. Explain the following terms:

(a) Lahars

(b) Nuées ardentes

2. Explain what geothermal energy is.

3. Where is geothermal energy widely used?

4. List four negative effects of volcanic activity.

5. Give an example of volcanic activity that has had negative effects on a local population.

?

Fig 3.26 The effect of volcanic dust in the atmosphere following the eruption of Mount St Helens

NOTE

The eruption of Eyjafjallajökull in April 2010 in Iceland caused enormous disruption to air travel for a period of 6 days. This is the greatest level of air travel disruptions experienced in Europe since World War II.

!

Questions

3232

Ordinary Level|Short Questions

Volcanoes 1. Examine the diagram of a volcano shown

below.

Use the following terms to identify the blanks on the diagram.

�� Vent

�� Secondary cone

�� Ash cloud

�� Crater

�� Magma chamber

2008, Part 1, Q6, 10 marks

Ordinary Level|Long QuestionsVolcanoes 2. Volcanoes can have both negative and

positive effects on the landscape and on people. Explain one negative and one positive effect of volcanoes.

2009, Part 2, Q1C, 40 marks


Positive effect 2 marks

Explaining the effect: 6 SRPs @ 3 marks each 18 marks

Negative effect 2 marks

Explaining the effect: 6 SRPs @ 3 marks each 18 marks

Total 40 marks

Higher Level|Short QuestionsHeight of volcanoes

3. The table below shows the height of some well-known volcanoes around the world.

Name and location Height in metres

Vesuvius – Italy 1281Krakatoa – Indonesia 813Fuji – Japan 3776Rainier – USA 4392St Helens – USA 2549Stromboli – Italy 924

Use graph paper to draw a graph that shows the data in the table above.



Vertical axis labelled – circle 3 marks

Horizontal axis labelled – centred 3 marks

Six items @ 4 marks each 24 marks

Total 30 marks

Higher Level|Long Questions

Satellite images – volcano 4. Name an example of a volcano which you

have studied. State two advantages and one disadvantage for people living in a volcanic region.


EXAM HINTS

Remember to read the question carefully. You need to include two advantages in your answer.

�

Volcanoes 5. Examine the processes that have led to the

formation of any two volcanic landforms.2006, Part 2, Q3C, 30 marks

EXAM HINTS

You will be awarded marks for using graph paper for any question that requires you to draw a graph.

�

3333

Effects of volcanic activity:

Negative Positive

1. Lahars 1. Fertile soils 2. Damage to property 2. Tourism 3. Nuée ardentes 3. Geothermal energy 4. Loss of life 4. Creation of new land 5. Destruction by fire 5. Building materials 6. Effect on environment

�� Central vent eruptions: destructive plate boundaries�� cone-shaped volcano

�� Fissure eruptions:�� Constructive plate boundaries�� Basic lava flows out onto surface by means of fissure�� May build up to form basalt plateau – Antrim-Derry

Plateau�� Flat landscape – Antrim-Derry Plateau

�� Hot spots: unusually warm areas of magma found beneath the Earth’s surface, within the mantle

�� Hydrothermal areas:�� Geysers, e.g. Old Faithful Yellow Stone National Park,

USA�� Hot springs, e.g. Iceland�� Black smokers, found at mid-ocean ridges, hot water

(700 ºC+) rises but through vent on ocean floor

Instruments used:�� Tiltmeters: identify

bulging on side of volcano

�� Seismograph: measures earthquake activity

Volcanic activity occurs at:�� Constructive plate boundaries�� Destructive plate boundaries�� Hotspots

Categories of volcano:�� Active: erupts regularly e.g. Mt Etna, Italy�� Dormant: has not erupted for a long time,

e.g. Cotopaxi, Peru�� Extinct: has not erupted in recorded history,

e.g. Slemish Mountain, Co. Antrim.

Volcanic materials ejected during eruption:�� Volcanic ash�� Rock particles�� Dust�� Gases�� Two types of lava:

�� acidic lava: high silica content�� basic lava: low silica content

�� Three types of lava flow: �� Pahoehoe lava�� Aa lava�� Pillow lava

�� Intrusive structures form when magma doesn’t reach the surface – forms intrusive rock, e.g. granite (plutonic/intrusive rocks)

�� Extrusive structures form on the surface of the earth – form extrusive rocks

Batholiths – intrusive structure:�� Leinster Batholith

�� Magma forced into crust, then cools and solidifies to form an intrusive rock, e.g. granite

�� Formation of Wicklow and Dublin Mountains�� Batholiths usually surrounded by metamorphic rock

Other intrusive features:

�� Sills�� Dykes�� Laccolith�� Lopolith

Extrusive structures, e.g. volcanoes – vary in shape:

�� Shield volcano�� Volcanic dome�� Composite volcano�� Cinder volcano

Volcanic activity prediction based on geologists’ study of:

�� Volcano formation�� Type of deposits�� Date of deposits�� Patterns of events�� Locations of volcanic eruptions�� Gases and temperatures and

steam

Mount St Helens 18 May, 1980 eruption

MIND M APThe Geography of Volcanoes Chapter 3

of

e.g. hape:

Volcanic activity

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