The Restless Earth

Unit 1 Physical Geography: The Restless EarthUnit Lessons• Why is the earth’s crust so unstable?• What happens at plate margins? • How are our highest and deepest places created? • How do people use an area of fold mountains? • How and where are volcanoes created? • How do volcanoes affect people? • How can we monitor volcanoes and predict eruptions? • What is a supervolcano? • What are earthquakes and where do they occur? • What were the causes, effects and responses to the Kobe earthquake? • What were the causes, effects and responses to the Port au Prince

earthquake? • Why is a tsunami hazardous?Independent study• An account of the uses of fold mountains and adapting to life in Livigno,

The Alps• A report of the eruption of Mount St Helens, USA on 18th May 1980• A comparison of the earthquakes in Kobe, Japan and Port au Prince, Haiti

Why is the earth’s crust so unstable?

Learning Objectives• To know the structure of the Earth• To understand the crust is unstable, especially at plate margins• To contrast oceanic and continental crust • To describe the distribution of plate margins and tectonic activity

Key terms: Crust, plate, plate margin, mantle, oceanic crust, continental crust, convection currents, destructive-subduction boundary, destructive-collision boundary, constructive boundary, conservative boundary

L

The structure of the Earth• Inner core - the centre and

hottest part of the Earth. Its solid and made up of iron and nickel. Temperatures up to 5500°C. Its immense heat energy acts like the engine room of the Earth.

• Outer core - surrounds the inner core. A liquid layer, also made up of iron and nickel. Still extremely hot, temperatures similar to inner core.

• Mantle - widest section of the Earth. Diameter of approximately 2900km. Made up of semi-molten rock called magma. In the upper parts of the mantle the rock is hard, but lower down the rock is soft and beginning to melt.

• Crust - outer layer of the earth. A thin layer between 0-60km thick. The crust is split into solid tectonic plates, upon which we live.

Convection currents operate in the mantle. These determine which way the plates move.

Contrasts between oceanic and continental crust

Oceanic crust• Newer, most

less than 200 million years old

• Denser• Can be

subducted (sink)

• Can be renewed and destroyed

Continental crust• Older, most

over 1500 million years old

• Less dense• Cannot be

subducted (sink)

• Cannot be renewed and destroyed

African PlateIndo Australian Plate

North American

Eurasian

Pacific

Nazca

Antarctic

South American

The Plates

TASK Label your plates map. Remember the plates move (shown by the arrows). They move at the

rate your finger nails grow.

Direction of plate movement

Figure 1 below is a map of the earth’s tectonic plates and the places where earthquakes occur worldwide. Describe how the distribution of earthquakes is linked to the earth’s tectonic plates (3 marks)

Exam Technique Describing Distributions

Describing distributions is very important in Geography. You need to be able to use this skill in all your GCSE units. When describing a distribution use the acronym H.L.GT.A (highest, lowest areas, general trend, anomalies).

Highest frequency of earthquakes around the Pacific Plate.

Less earthquakes at this between the North America Plate and the Eurasian

Earthquakes occur most where plates are moving towards or sliding past another

Less earthquakes when the plates are moving apart

Plate margins – types, direction & examples TASK Study map C on page 9. Fill in the table below.

Plate Margin Direction of plate Movement

Example of plate margin

Destructive - subduction

Oceanic plate moves into and subducts beneath continental plate

Juan de Fuca Plate (oceanic) subducts beneath North American Plate (continental)

Destructive – collision

Two continental plates collide, both forced upwards (forming fold mountains)

Indo-Australian Plate (continental) collides with the Eurasian Plate (forms Himalayas)

Constructive Two plates move away from each other (new land created by rising magma)

North American Plate and the Eurasian Plate (forms Mid Atlantic Ridge)

Conservative Two plates slide past one another (neither is destroyed)

North American Plate slides past the Pacific Plate (forms San Andreas Fault)

Click to reveal the answers…

Questions

1. Draw simple labelled diagram contrasting oceanic and continental crust. Be sure to give three differences between oceanic and continental crust. (4 marks)

2. What are convection currents? How do they drive the movement of plates above? (3 marks)

3. Describe how the distribution of earthquakes is linked to the earth’s tectonic plates (3 marks)

4. At which plate margins do earthquakes occur at most frequently? (2 marks)

Use pages 8 and 9 to help you with these questions