Year 9 Revision

Winter exam

RESTLESS EARTH

Structure of the Earth

• The Earth is made up of 3 main layers:– Core– Mantle– Crust

Inner core

Outer core

Mantle

Crust

World Plates

What are earthquakes and where do they occur?

Earthquakes are vibrations caused by movements at plate margins and at fault lines (cracks in the earth’s surface).

They can occur at all 4 major plate boundaries but the most severe earthquakes are normally found at CONSERVATIVE and DESTRUCTIVE plate margins.

CONSERVATIVE

DESTRUCTIVE

Why do earthquakes happen?

How can we measure earthquakes?

The largest earthquake ever recorded was in Chile. It measured 8.9 on the Richter Scale.

This measures the magnitude of a tremor (how powerful it is) using an instrument called a seismograph.

On the Richter Scale, magnitude is expressed in whole numbers and fractions.

It is a logarithmic scale which means that a size ‘6’ on the Richter Scale is 10 times larger than a size ’5’ and 100 times larger than a size ‘4’.

1234

65

987

10

Richter Scale

The Richter Scale

Mercalli Scale

This measures how much damage is caused by the earthquake based on observations. It is measured on a scale between I and XII.

Mercalli Scale

Epicentre and focus

predict plan protect

1. predict

water levels can rise in wells and lakes because of cracks in the rock

foreshocks before the main quake can be detected by a seismometer

animals can act strangely before the earthquake

a tiltmeter can check any movement within the rocks

How can we limit earthquake damage?

2. plan

What should people pack in their emergency kit?

make an emergency plan

organize regular ‘earthquake practices’ for offices and schools

advise people to plan for an earthquake (eg tell them to turn off the gas, find a ‘safe’ place in their homes, pack an emergency kit)

enforce regulations to make some buildings earthquake proof

Design a poster reminding people what to do in an earthquake.

How can we limit earthquake damage?

Impacts

Primary Secondary

TSUNAMI

• What do you know?

What caused the tsunami?

•Volcanic bombs, ash, lava, gases

•Magma chamber

•Parasitic cone

•Crater

•Main vent

VOLCANOES

At destructive plate boundaries the lava is viscous (thick like treacle) and it cannot flow very far from the volcano’s vent. This makes the volcano steep sided.

At constructive plate boundaries the lava is runny and it can flow far away from the volcano’s vent. This makes the volcano gentle sided.

Active volcano – liable to erupt e.g. Mt Etna.

Dormant (sleeping) volcano – a volcano which has not erupted for many years. For example, Mt Pinatubo erupted in 1991 after 500 years of dormancy.

Extinct volcano – a volcano which has not erupted for many thousands or millions of years e.g. Edinburgh.

However, it is often very difficult to tell whether a volcano will erupt again…El Chichon, Mexico erupted in 1982 after being dormant for approximately 1200 years!

Do all volcanoes erupt?

Mt St Helens – the eruption

This lava is weathered (broken down) to form a fertile soil,

Tourists are attracted to areas of volcanic activity.

Geothermal energy (heat from the earth) can be produced in many volcanic areas.

Can you think of any other reasons?

Why do people live in volcanic areas?

EXTREME WEATHER

HURRICANES

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How do hurricanes form?

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Hurricane Katrina hit New Orleans on the morning of the 29th August 2005 bringing with it terrible destruction.

Winds of over 250 kilometres per hour were recorded as Katrina hit the coast, causing a storm surge8.5 metres high. New Orleans

Hurricane Katrina

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80% of the city was flooded and over a million homes were left without electricity.Over 1,800 deaths werecaused by the storm, around700 of them in New Orleans.

In some areas the flood level rose to over six metres. Thosethat had decided to stay in theirhomes had to either find highground and await rescue or risk swimming and wadingthrough polluted floodwater.

Effects of Hurricane Katrina

TORNADOES – do you know the answers to these questions?

1. Why do they happen?2. What states do you find in Tornado Alley?3. What is Tornado Watch?4. What is Tornado Warning?5. What is the Fujita scale?