Year 9 Revision
Winter exam
RESTLESS EARTH
Structure of the Earth
•The Earth is madeup of 3 mainlayers:
–Core
–Mantle
–Crust
Inner core
Outer core
Mantle
Crust
World Plates
What are earthquakes and where do they occur?
Earthquakes are vibrations causedby movements at plate marginsand at fault lines (cracks in theearth’s surface).
They can occur at all 4 major plateboundaries but the most severeearthquakes are normally found atCONSERVATIVE andDESTRUCTIVE plate margins.
CONSERVATIVE
DESTRUCTIVE
Why do earthquakes happen?
How can we measure earthquakes?
The largest earthquakeever recorded was inChile. It measured 8.9on the Richter Scale.
This measures the magnitude of a tremor (howpowerful it is) using an instrument called aseismograph.
On the Richter Scale, magnitude is expressed inwhole numbers and fractions.
It is a logarithmic scale which means that a size‘6’ on the Richter Scale is 10 times larger than asize ’5’ and 100 times larger than a size ‘4’.
1
2
3
4
6
5
9
8
7
10
RichterScale
The Richter Scale
Mercalli Scale
This measureshow muchdamage iscaused by theearthquakebased onobservations. Itis measured on ascale between Iand XII.
Mercalli Scale
Epicentre and focus
predict
plan
protect
1. predict
water levels can rise in wells andlakes because of cracks in therock
foreshocks before the main quakecan be detected by a seismometer
animals can act strangely beforethe earthquake
a tiltmeter can check any movementwithin the rocks
How can we limit earthquake damage?
2. plan
What should people pack in their emergency kit?
make an emergency plan
organize regular ‘earthquakepractices’ for offices andschools
advise people to plan for anearthquake (eg tell them to turn offthe gas, find a ‘safe’ place in theirhomes, pack an emergency kit)
enforce regulations to makesome buildings earthquakeproof
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 itcannot flow very far from the volcano’s vent. This makes the volcano steepsided.
At constructive plate boundaries the lava is runny and it can flow far away fromthe 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 eruptedfor many years. For example, Mt Pinatubo erupted in 1991 after500 years of dormancy.
Extinct volcano – a volcano which has not erupted for manythousands or millions of years e.g. Edinburgh.
However, it is often very difficult to tell whether a volcano will eruptagain…El Chichon, Mexico erupted in 1982 after being dormant forapproximately 1200 years!
Do all volcanoes erupt?
Mt St Helens – the eruption
This lava is weathered(broken down) to form afertile soil,
Tourists are attracted to areas ofvolcanic activity.
Geothermal energy (heat fromthe earth) can be produced inmany volcanic areas.
Can you think of any other reasons?
Why do people live in volcanic areas?
EXTREME WEATHER
HURRICANES
22
How do hurricanes form?
23
Hurricane Katrina hit New Orleanson the morning of the 29th August2005 bringing with itterrible destruction.
Winds of over 250 kilometresper hour were recorded asKatrina hit the coast,causing a storm surge8.5 metres high.
New Orleans
Hurricane Katrina
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80% of the city was flooded andover a million homes were leftwithout electricity.Over 1,800 deaths werecaused by the storm, around700 of them in New Orleans.
In some areas the flood levelrose to over six metres. Thosethat had decided to stay in theirhomes had to either find highground and await rescue orrisk 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?